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path: root/test/data/html/web-apps.html
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01//EN">

<html lang=en-GB-hixie>
 <head>
  <title>HTML 5</title>
  <link href="/style/specification" rel=stylesheet type="text/css">
  <link href="/images/icon" rel=icon>

  <style type="text/css">
   h4 + .element { margin-top: -2.5em; padding-top: 2em; }
   h4 + p + .element { margin-top: -5em; padding-top: 4em; }
   .element { background: #EEFFEE; color: black; margin: 0 0 1em -1em; padding: 0 1em 0.25em 0.75em; border-left: solid #99FF99 0.25em; -padding: 0; /* that last decl is for IE6. Try removing it, it's hilarious! */ }
   .proposal { border: blue solid; padding: 1em; }
   table.matrix, table.matrix td { border: none; text-align: right; }
   table.matrix { margin-left: 2em; }
  </style>

 <body class=draft>
  <div class=head>
   <p><a class=logo href="http://www.whatwg.org/" rel=home><img alt=WHATWG
    src="/images/logo"></a></p>

   <h1 id=html-5>HTML 5</h1>

   <h2 class="no-num no-toc" id=working>Working Draft &mdash; 14 June 2007</h2>

   <p>You can take part in this work. <a
    href="http://www.whatwg.org/mailing-list">Join the working group's
    discussion list.</a></p>

   <p><strong>Web designers!</strong> We have a <a
    href="http://blog.whatwg.org/faq/">FAQ</a>, a <a
    href="http://forums.whatwg.org/">forum</a>, and a <a
    href="http://www.whatwg.org/mailing-list#help">help mailing list</a> for
    you!</p>

   <dl>
    <dt>One-page version:

    <dd><a
     href="http://www.whatwg.org/specs/web-apps/current-work/">http://www.whatwg.org/specs/web-apps/current-work/</a>

    <dt>Multiple-page version:

    <dd><a
     href="http://www.whatwg.org/specs/web-apps/current-work/multipage/">http://www.whatwg.org/specs/web-apps/current-work/multipage/</a>

    <dt>Version history:

    <dd>Twitter messages (non-editorial changes only): <a
     href="http://twitter.com/WHATWG">http://twitter.com/WHATWG</a>

    <dd>Commit-Watchers mailing list: <a
     href="http://lists.whatwg.org/listinfo.cgi/commit-watchers-whatwg.org">http://lists.whatwg.org/listinfo.cgi/commit-watchers-whatwg.org</a>

    <dd>Interactive Web interface: <a
     href="http://html5.org/tools/web-apps-tracker">http://html5.org/tools/web-apps-tracker</a>

    <dd>Subversion interface: <a
     href="http://svn.whatwg.org/">http://svn.whatwg.org/</a>

    <dt>Editor:

    <dd>Ian Hickson, Google, ian@hixie.ch
   </dl>

   <p class=copyright>&copy; Copyright 2004-2007 Apple Computer, Inc.,
    Mozilla Foundation, and Opera Software ASA.</p>

   <p class=copyright>You are granted a license to use, reproduce and create
    derivative works of this document.</p>
  </div>

  <hr>

  <h2 class="no-num no-toc" id=abstract>Abstract</h2>

  <p>This specification introduces features to HTML and the DOM that ease the
   authoring of Web-based applications. Additions include the context menus,
   a direct-mode graphics canvas, inline popup windows, and server-sent
   events.

  <h2 class="no-num no-toc" id=status>Status of this document</h2>

  <p><strong>This is a work in progress!</strong> This document is changing
   on a daily if not hourly basis in response to comments and as a general
   part of its development process. Comments are very welcome, please send
   them to <a href="mailto:whatwg@whatwg.org">whatwg@whatwg.org</a>. Thank
   you.

  <p>Implementors should be aware that this specification is not stable.
   <strong>Implementors who are not taking part in the discussions are likely
   to find the specification changing out from under them in incompatible
   ways.</strong> Vendors interested in implementing this specification
   before it eventually reaches the call for implementations should join the
   <a href="/mailing-list">WHATWG mailing list</a> and take part in the
   discussions.

  <p>This specification is also being produced by the <a
   href="http://www.w3.org/html/wg">W3C HTML WG</a>. The two specifications
   are identical from the table of contents onwards.

  <p>This specification is intended to replace (be the new version of) what
   was previously the HTML4, XHTML 1.x, and DOM2 HTML specifications.

  <h3 class="no-num no-toc" id=stability0>Stability</h3>

  <p>Different parts of this specification are at different levels of
   maturity.

  <div id=stability></div>

  <p class=big-issue>Known issues are usually marked like this. There are
   some spec-wide issues that have not yet been addressed: case-sensitivity
   is a very poorly handled topic right now, and the firing of events needs
   to be unified (right now some bubble, some don't, they all use different
   text to fire events, etc).

  <h2 class="no-num no-toc" id=contents>Table of contents</h2>
  <!--begin-toc-->

  <ul class=toc>
   <li><a href="#introduction"><span class=secno>1. </span>Introduction</a>
    <ul class=toc>
     <li><a href="#scope"><span class=secno>1.1. </span>Scope</a>
      <ul class=toc>
       <li><a href="#relationship"><span class=secno>1.1.1.
        </span>Relationship to HTML 4.01, XHTML 1.1, DOM2 HTML</a>

       <li><a href="#relationship0"><span class=secno>1.1.2.
        </span>Relationship to XHTML2</a>

       <li><a href="#relationship1"><span class=secno>1.1.3.
        </span>Relationship to XUL, Flash, Silverlight, and other proprietary
        UI languages</a>
      </ul>

     <li><a href="#structure"><span class=secno>1.2. </span>Structure of this
      specification</a>
      <ul class=toc>
       <li><a href="#how-to"><span class=secno>1.2.1. </span>How to read this
        specification</a>
      </ul>

     <li><a href="#conformance"><span class=secno>1.3. </span>Conformance
      requirements</a>
      <ul class=toc>
       <li><a href="#common"><span class=secno>1.3.1. </span>Common
        conformance requirements for APIs exposed to JavaScript</a>

       <li><a href="#dependencies"><span class=secno>1.3.2.
        </span>Dependencies</a>

       <li><a href="#features"><span class=secno>1.3.3. </span>Features
        defined in other specifications</a>
      </ul>

     <li><a href="#terminology"><span class=secno>1.4. </span>Terminology</a>
      
      <ul class=toc>
       <li><a href="#html-vs"><span class=secno>1.4.1. </span>HTML vs
        XHTML</a>
      </ul>
    </ul>

   <li><a href="#dom"><span class=secno>2. </span>The Document Object
    Model</a>
    <ul class=toc>
     <li><a href="#documents"><span class=secno>2.1. </span>Documents</a>
      <ul class=toc>
       <li><a href="#security"><span class=secno>2.1.1. </span>Security</a>

       <li><a href="#resource"><span class=secno>2.1.2. </span>Resource
        metadata management</a>
      </ul>

     <li><a href="#elements"><span class=secno>2.2. </span>Elements</a>
      <ul class=toc>
       <li><a href="#reflecting"><span class=secno>2.2.1. </span>Reflecting
        content attributes in DOM attributes</a>
      </ul>

     <li><a href="#common0"><span class=secno>2.3. </span>Common DOM
      interfaces</a>
      <ul class=toc>
       <li><a href="#collections"><span class=secno>2.3.1.
        </span>Collections</a>
        <ul class=toc>
         <li><a href="#htmlcollection"><span class=secno>2.3.1.1.
          </span>HTMLCollection</a>

         <li><a href="#htmlformcontrolscollection"><span class=secno>2.3.1.2.
          </span>HTMLFormControlsCollection</a>

         <li><a href="#htmloptionscollection"><span class=secno>2.3.1.3.
          </span>HTMLOptionsCollection</a>
        </ul>

       <li><a href="#domtokenlist"><span class=secno>2.3.2.
        </span>DOMTokenList</a>

       <li><a href="#dom-feature"><span class=secno>2.3.3. </span>DOM feature
        strings</a>
      </ul>

     <li><a href="#dom-tree"><span class=secno>2.4. </span>DOM tree
      accessors</a>

     <li><a href="#dynamic"><span class=secno>2.5. </span>Dynamic markup
      insertion</a>
      <ul class=toc>
       <li><a href="#controlling"><span class=secno>2.5.1. </span>Controlling
        the input stream</a>

       <li><a href="#dynamic0"><span class=secno>2.5.2. </span>Dynamic markup
        insertion in HTML</a>

       <li><a href="#dynamic1"><span class=secno>2.5.3. </span>Dynamic markup
        insertion in XML</a>
      </ul>

     <li><a href="#apis-in"><span class=secno>2.6. </span>APIs in HTML
      documents</a>
    </ul>

   <li><a href="#semantics"><span class=secno>3. </span>Semantics and
    structure of HTML elements</a>
    <ul class=toc>
     <li><a href="#semantics-intro"><span class=secno>3.1.
      </span>Introduction</a>

     <li><a href="#common1"><span class=secno>3.2. </span>Common
      microsyntaxes</a>
      <ul class=toc>
       <li><a href="#common2"><span class=secno>3.2.1. </span>Common parser
        idioms</a>

       <li><a href="#boolean"><span class=secno>3.2.2. </span>Boolean
        attributes</a>

       <li><a href="#numbers"><span class=secno>3.2.3. </span>Numbers</a>
        <ul class=toc>
         <li><a href="#unsigned"><span class=secno>3.2.3.1. </span>Unsigned
          integers</a>

         <li><a href="#signed"><span class=secno>3.2.3.2. </span>Signed
          integers</a>

         <li><a href="#real-numbers"><span class=secno>3.2.3.3. </span>Real
          numbers</a>

         <li><a href="#ratios"><span class=secno>3.2.3.4. </span>Ratios</a>

         <li><a href="#percentages-and-dimensions"><span class=secno>3.2.3.5.
          </span>Percentages and dimensions</a>

         <li><a href="#lists"><span class=secno>3.2.3.6. </span>Lists of
          integers</a>
        </ul>

       <li><a href="#dates"><span class=secno>3.2.4. </span>Dates and
        times</a>
        <ul class=toc>
         <li><a href="#specific"><span class=secno>3.2.4.1. </span>Specific
          moments in time</a>

         <li><a href="#vaguer"><span class=secno>3.2.4.2. </span>Vaguer
          moments in time</a>
        </ul>

       <li><a href="#time-offsets"><span class=secno>3.2.5. </span>Time
        offsets</a>

       <li><a href="#tokens"><span class=secno>3.2.6. </span>Tokens</a>

       <li><a href="#keywords"><span class=secno>3.2.7. </span>Keywords and
        enumerated attributes</a>

       <li><a href="#syntax-references"><span class=secno>3.2.8.
        </span>References</a>
      </ul>

     <li><a href="#documents0"><span class=secno>3.3. </span>Documents and
      document fragments</a>
      <ul class=toc>
       <li><a href="#semantics0"><span class=secno>3.3.1.
        </span>Semantics</a>

       <li><a href="#structure0"><span class=secno>3.3.2.
        </span>Structure</a>

       <li><a href="#kinds"><span class=secno>3.3.3. </span>Kinds of
        elements</a>
        <ul class=toc>
         <li><a href="#block-level"><span class=secno>3.3.3.1.
          </span>Block-level elements</a>

         <li><a href="#inline-level"><span class=secno>3.3.3.2.
          </span>Inline-level content</a>

         <li><a href="#transparent"><span class=secno>3.3.3.3.
          </span>Transparent content models</a>

         <li><a href="#determining"><span class=secno>3.3.3.4.
          </span>Determining if a particular element contains block-level
          elements or inline-level content</a>

         <li><a href="#interactive0"><span class=secno>3.3.3.5.
          </span>Interactive elements</a>

         <li><a href="#paragraphs"><span class=secno>3.3.3.6.
          </span>Paragraphs</a>
        </ul>
      </ul>

     <li><a href="#global"><span class=secno>3.4. </span>Global
      attributes</a>
      <ul class=toc>
       <li><a href="#the-id"><span class=secno>3.4.1. </span>The
        <code>id</code> attribute</a>

       <li><a href="#the-title"><span class=secno>3.4.2. </span>The
        <code>title</code> attribute</a>

       <li><a href="#the-lang"><span class=secno>3.4.3. </span>The
        <code>lang</code> (HTML only) and <code>xml:lang</code> (XML only)
        attributes</a>

       <li><a href="#the-dir"><span class=secno>3.4.4. </span>The
        <code>dir</code> attribute</a>

       <li><a href="#classes"><span class=secno>3.4.5. </span>The
        <code>class</code> attribute</a>

       <li><a href="#the-irrelevant"><span class=secno>3.4.6. </span>The
        <code>irrelevant</code> attribute</a>
      </ul>

     <li><a href="#interaction"><span class=secno>3.5. </span>Interaction</a>
      
      <ul class=toc>
       <li><a href="#activation"><span class=secno>3.5.1.
        </span>Activation</a>

       <li><a href="#focus"><span class=secno>3.5.2. </span>Focus</a>
        <ul class=toc>
         <li><a href="#focus-management"><span class=secno>3.5.2.1.
          </span>Focus management</a>

         <li><a href="#sequential"><span class=secno>3.5.2.2.
          </span>Sequential focus navigation</a>
        </ul>

       <li><a href="#scrolling"><span class=secno>3.5.3. </span>Scrolling
        elements into view</a>
      </ul>

     <li><a href="#the-root"><span class=secno>3.6. </span>The root
      element</a>
      <ul class=toc>
       <li><a href="#the-html"><span class=secno>3.6.1. </span>The
        <code>html</code> element</a>
      </ul>

     <li><a href="#document"><span class=secno>3.7. </span>Document
      metadata</a>
      <ul class=toc>
       <li><a href="#the-head"><span class=secno>3.7.1. </span>The
        <code>head</code> element</a>

       <li><a href="#the-title0"><span class=secno>3.7.2. </span>The
        <code>title</code> element</a>

       <li><a href="#the-base"><span class=secno>3.7.3. </span>The
        <code>base</code> element</a>

       <li><a href="#the-link"><span class=secno>3.7.4. </span>The
        <code>link</code> element</a>

       <li><a href="#meta"><span class=secno>3.7.5. </span>The
        <code>meta</code> element</a>
        <ul class=toc>
         <li><a href="#standard"><span class=secno>3.7.5.1. </span>Standard
          metadata names</a>

         <li><a href="#other"><span class=secno>3.7.5.2. </span>Other
          metadata names</a>

         <li><a href="#pragma"><span class=secno>3.7.5.3. </span>Pragma
          directives</a>

         <li><a href="#charset"><span class=secno>3.7.5.4. </span>Specifying
          and establishing the document's character encoding</a>
        </ul>

       <li><a href="#the-style"><span class=secno>3.7.6. </span>The
        <code>style</code> element</a>

       <li><a href="#styling"><span class=secno>3.7.7. </span>Styling</a>
      </ul>

     <li><a href="#sections"><span class=secno>3.8. </span>Sections</a>
      <ul class=toc>
       <li><a href="#the-body"><span class=secno>3.8.1. </span>The
        <code>body</code> element</a>

       <li><a href="#the-section"><span class=secno>3.8.2. </span>The
        <code>section</code> element</a>

       <li><a href="#the-nav"><span class=secno>3.8.3. </span>The
        <code>nav</code> element</a>

       <li><a href="#the-article"><span class=secno>3.8.4. </span>The
        <code>article</code> element</a>

       <li><a href="#the-blockquote"><span class=secno>3.8.5. </span>The
        <code>blockquote</code> element</a>

       <li><a href="#the-aside"><span class=secno>3.8.6. </span>The
        <code>aside</code> element</a>

       <li><a href="#the-h1"><span class=secno>3.8.7. </span>The
        <code>h1</code>, <code>h2</code>, <code>h3</code>, <code>h4</code>,
        <code>h5</code>, and <code>h6</code> elements</a>

       <li><a href="#the-header"><span class=secno>3.8.8. </span>The
        <code>header</code> element</a>

       <li><a href="#the-footer"><span class=secno>3.8.9. </span>The
        <code>footer</code> element</a>

       <li><a href="#the-address"><span class=secno>3.8.10. </span>The
        <code>address</code> element</a>

       <li><a href="#headings"><span class=secno>3.8.11. </span>Headings and
        sections</a>
        <ul class=toc>
         <li><a href="#outlines"><span class=secno>3.8.11.1. </span>Creating
          an outline</a>

         <li><a href="#associatedSection"><span class=secno>3.8.11.2.
          </span>Determining which heading and section applies to a
          particular node</a>

         <li><a href="#distinguishing"><span class=secno>3.8.11.3.
          </span>Distinguishing site-wide headers from page headers</a>
        </ul>
      </ul>

     <li><a href="#prose"><span class=secno>3.9. </span>Prose</a>
      <ul class=toc>
       <li><a href="#the-p"><span class=secno>3.9.1. </span>The
        <code>p</code> element</a>

       <li><a href="#the-hr"><span class=secno>3.9.2. </span>The
        <code>hr</code> element</a>

       <li><a href="#the-br"><span class=secno>3.9.3. </span>The
        <code>br</code> element</a>

       <li><a href="#the-dialog"><span class=secno>3.9.4. </span>The
        <code>dialog</code> element</a>
      </ul>

     <li><a href="#preformatted"><span class=secno>3.10. </span>Preformatted
      text</a>
      <ul class=toc>
       <li><a href="#the-pre"><span class=secno>3.10.1. </span>The
        <code>pre</code> element</a>
      </ul>

     <li><a href="#lists0"><span class=secno>3.11. </span>Lists</a>
      <ul class=toc>
       <li><a href="#the-ol"><span class=secno>3.11.1. </span>The
        <code>ol</code> element</a>

       <li><a href="#the-ul"><span class=secno>3.11.2. </span>The
        <code>ul</code> element</a>

       <li><a href="#the-li"><span class=secno>3.11.3. </span>The
        <code>li</code> element</a>

       <li><a href="#the-dl"><span class=secno>3.11.4. </span>The
        <code>dl</code> element</a>

       <li><a href="#the-dt"><span class=secno>3.11.5. </span>The
        <code>dt</code> element</a>

       <li><a href="#the-dd"><span class=secno>3.11.6. </span>The
        <code>dd</code> element</a>
      </ul>

     <li><a href="#phrase"><span class=secno>3.12. </span>Phrase elements</a>
      
      <ul class=toc>
       <li><a href="#the-a"><span class=secno>3.12.1. </span>The
        <code>a</code> element</a>

       <li><a href="#the-q"><span class=secno>3.12.2. </span>The
        <code>q</code> element</a>

       <li><a href="#the-cite"><span class=secno>3.12.3. </span>The
        <code>cite</code> element</a>

       <li><a href="#the-em"><span class=secno>3.12.4. </span>The
        <code>em</code> element</a>

       <li><a href="#the-strong"><span class=secno>3.12.5. </span>The
        <code>strong</code> element</a>

       <li><a href="#the-small"><span class=secno>3.12.6. </span>The
        <code>small</code> element</a>

       <li><a href="#the-m"><span class=secno>3.12.7. </span>The
        <code>m</code> element</a>

       <li><a href="#the-dfn"><span class=secno>3.12.8. </span>The
        <code>dfn</code> element</a>

       <li><a href="#the-abbr"><span class=secno>3.12.9. </span>The
        <code>abbr</code> element</a>

       <li><a href="#the-time"><span class=secno>3.12.10. </span>The
        <code>time</code> element</a>

       <li><a href="#the-meter"><span class=secno>3.12.11. </span>The
        <code>meter</code> element</a>

       <li><a href="#the-progress"><span class=secno>3.12.12. </span>The
        <code>progress</code> element</a>

       <li><a href="#the-code"><span class=secno>3.12.13. </span>The
        <code>code</code> element</a>

       <li><a href="#the-var"><span class=secno>3.12.14. </span>The
        <code>var</code> element</a>

       <li><a href="#the-samp"><span class=secno>3.12.15. </span>The
        <code>samp</code> element</a>

       <li><a href="#the-kbd"><span class=secno>3.12.16. </span>The
        <code>kbd</code> element</a>

       <li><a href="#the-sup"><span class=secno>3.12.17. </span>The
        <code>sup</code> and <code>sub</code> elements</a>

       <li><a href="#the-span"><span class=secno>3.12.18. </span>The
        <code>span</code> element</a>

       <li><a href="#the-i"><span class=secno>3.12.19. </span>The
        <code>i</code> element</a>

       <li><a href="#the-b"><span class=secno>3.12.20. </span>The
        <code>b</code> element</a>

       <li><a href="#the-bdo"><span class=secno>3.12.21. </span>The
        <code>bdo</code> element</a>
      </ul>

     <li><a href="#edits"><span class=secno>3.13. </span>Edits</a>
      <ul class=toc>
       <li><a href="#the-ins"><span class=secno>3.13.1. </span>The
        <code>ins</code> element</a>

       <li><a href="#the-del"><span class=secno>3.13.2. </span>The
        <code>del</code> element</a>

       <li><a href="#attributes"><span class=secno>3.13.3. </span>Attributes
        common to <code>ins</code> and <code>del</code> elements</a>
      </ul>

     <li><a href="#embedded"><span class=secno>3.14. </span>Embedded
      content</a>
      <ul class=toc>
       <li><a href="#the-figure"><span class=secno>3.14.1. </span>The
        <code>figure</code> element</a>

       <li><a href="#the-img"><span class=secno>3.14.2. </span>The
        <code>img</code> element</a>

       <li><a href="#the-iframe"><span class=secno>3.14.3. </span>The
        <code>iframe</code> element</a>

       <li><a href="#the-embed"><span class=secno>3.14.4. </span>The
        <code>embed</code> element</a>

       <li><a href="#the-object"><span class=secno>3.14.5. </span>The
        <code>object</code> element</a>

       <li><a href="#the-param"><span class=secno>3.14.6. </span>The
        <code>param</code> element</a>

       <li><a href="#video"><span class=secno>3.14.7. </span>The
        <code>video</code> element</a>
        <ul class=toc>
         <li><a href="#video0"><span class=secno>3.14.7.1. </span>Video and
          audio codecs for <code>video</code> elements</a>
        </ul>

       <li><a href="#audio"><span class=secno>3.14.8. </span>The
        <code>audio</code> element</a>
        <ul class=toc>
         <li><a href="#audio0"><span class=secno>3.14.8.1. </span>Audio
          codecs for <code>audio</code> elements</a>
        </ul>

       <li><a href="#media"><span class=secno>3.14.9. </span>Media
        elements</a>
        <ul class=toc>
         <li><a href="#error"><span class=secno>3.14.9.1. </span>Error
          codes</a>

         <li><a href="#location"><span class=secno>3.14.9.2. </span>Location
          of the media resource</a>

         <li><a href="#network0"><span class=secno>3.14.9.3. </span>Network
          states</a>

         <li><a href="#loading"><span class=secno>3.14.9.4. </span>Loading
          the media resource</a>

         <li><a href="#offsets"><span class=secno>3.14.9.5. </span>Offsets
          into the media resource</a>

         <li><a href="#the-ready"><span class=secno>3.14.9.6. </span>The
          ready states</a>

         <li><a href="#playing"><span class=secno>3.14.9.7. </span>Playing
          the media resource</a>

         <li><a href="#seeking"><span class=secno>3.14.9.8.
          </span>Seeking</a>

         <li><a href="#cue-points"><span class=secno>3.14.9.9. </span>Cue
          points</a>

         <li><a href="#user-interface"><span class=secno>3.14.9.10.
          </span>User interface</a>

         <li><a href="#time-range"><span class=secno>3.14.9.11. </span>Time
          range</a>

         <li><a href="#mediaevents"><span class=secno>3.14.9.12. </span>Event
          summary</a>

         <li><a href="#security0"><span class=secno>3.14.9.13.
          </span>Security and privacy considerations</a>
        </ul>

       <li><a href="#the-source"><span class=secno>3.14.10. </span>The
        <code>source</code> element</a>

       <li><a href="#the-canvas"><span class=secno>3.14.11. </span>The
        <code>canvas</code> element</a>
        <ul class=toc>
         <li><a href="#the-2d"><span class=secno>3.14.11.1. </span>The 2D
          context</a>
          <ul class=toc>
           <li><a href="#the-canvas0"><span class=secno>3.14.11.1.1.
            </span>The canvas state</a>

           <li><a href="#transformations"><span class=secno>3.14.11.1.2.
            </span>Transformations</a>

           <li><a href="#compositing"><span class=secno>3.14.11.1.3.
            </span>Compositing</a>

           <li><a href="#colors"><span class=secno>3.14.11.1.4. </span>Colors
            and styles</a>

           <li><a href="#line-styles"><span class=secno>3.14.11.1.5.
            </span>Line styles</a>

           <li><a href="#shadows"><span class=secno>3.14.11.1.6.
            </span>Shadows</a>

           <li><a href="#simple"><span class=secno>3.14.11.1.7. </span>Simple
            shapes (rectangles)</a>

           <li><a href="#complex"><span class=secno>3.14.11.1.8.
            </span>Complex shapes (paths)</a>

           <li><a href="#images"><span class=secno>3.14.11.1.9.
            </span>Images</a>

           <li><a href="#pixel"><span class=secno>3.14.11.1.10. </span>Pixel
            manipulation</a>

           <li><a href="#drawing"><span class=secno>3.14.11.1.11.
            </span>Drawing model</a>
          </ul>
        </ul>

       <li><a href="#the-map"><span class=secno>3.14.12. </span>The
        <code>map</code> element</a>

       <li><a href="#the-area"><span class=secno>3.14.13. </span>The
        <code>area</code> element</a>

       <li><a href="#image-maps"><span class=secno>3.14.14. </span>Image
        maps</a>
      </ul>

     <li><a href="#tabular"><span class=secno>3.15. </span>Tabular data</a>
      <ul class=toc>
       <li><a href="#the-table"><span class=secno>3.15.1. </span>The
        <code>table</code> element</a>

       <li><a href="#the-caption"><span class=secno>3.15.2. </span>The
        <code>caption</code> element</a>

       <li><a href="#the-colgroup"><span class=secno>3.15.3. </span>The
        <code>colgroup</code> element</a>

       <li><a href="#the-col"><span class=secno>3.15.4. </span>The
        <code>col</code> element</a>

       <li><a href="#the-tbody"><span class=secno>3.15.5. </span>The
        <code>tbody</code> element</a>

       <li><a href="#the-thead"><span class=secno>3.15.6. </span>The
        <code>thead</code> element</a>

       <li><a href="#the-tfoot"><span class=secno>3.15.7. </span>The
        <code>tfoot</code> element</a>

       <li><a href="#the-tr"><span class=secno>3.15.8. </span>The
        <code>tr</code> element</a>

       <li><a href="#the-td"><span class=secno>3.15.9. </span>The
        <code>td</code> element</a>

       <li><a href="#the-th"><span class=secno>3.15.10. </span>The
        <code>th</code> element</a>

       <li><a href="#processing"><span class=secno>3.15.11. </span>Processing
        model</a>
        <ul class=toc>
         <li><a href="#forming"><span class=secno>3.15.11.1. </span>Forming a
          table</a>

         <li><a href="#header-and-data-cell-semantics"><span
          class=secno>3.15.11.2. </span>Forming relationships between data
          cells and header cells</a>
        </ul>
      </ul>

     <li><a href="#forms"><span class=secno>3.16. </span>Forms</a>
      <ul class=toc>
       <li><a href="#the-form"><span class=secno>3.16.1. </span>The
        <code>form</code> element</a>

       <li><a href="#the-fieldset"><span class=secno>3.16.2. </span>The
        <code>fieldset</code> element</a>

       <li><a href="#the-input"><span class=secno>3.16.3. </span>The
        <code>input</code> element</a>

       <li><a href="#the-button"><span class=secno>3.16.4. </span>The
        <code>button</code> element</a>

       <li><a href="#the-label"><span class=secno>3.16.5. </span>The
        <code>label</code> element</a>

       <li><a href="#the-select"><span class=secno>3.16.6. </span>The
        <code>select</code> element</a>

       <li><a href="#the-datalist"><span class=secno>3.16.7. </span>The
        <code>datalist</code> element</a>

       <li><a href="#the-optgroup"><span class=secno>3.16.8. </span>The
        <code>optgroup</code> element</a>

       <li><a href="#the-option"><span class=secno>3.16.9. </span>The
        <code>option</code> element</a>

       <li><a href="#the-textarea"><span class=secno>3.16.10. </span>The
        <code>textarea</code> element</a>

       <li><a href="#the-output"><span class=secno>3.16.11. </span>The
        <code>output</code> element</a>

       <li><a href="#processing0"><span class=secno>3.16.12.
        </span>Processing model</a>
        <ul class=toc>
         <li><a href="#form-submission"><span class=secno>3.16.12.1.
          </span>Form submission</a>
        </ul>
      </ul>

     <li><a href="#scripting0"><span class=secno>3.17. </span>Scripting</a>
      <ul class=toc>
       <li><a href="#script"><span class=secno>3.17.1. </span>The
        <code>script</code> element</a>
        <ul class=toc>
         <li><a href="#scriptingLanguages"><span class=secno>3.17.1.1.
          </span>Scripting languages</a>
        </ul>

       <li><a href="#the-noscript"><span class=secno>3.17.2. </span>The
        <code>noscript</code> element</a>

       <li><a href="#the-event-source"><span class=secno>3.17.3. </span>The
        <code>event-source</code> element</a>
      </ul>

     <li><a href="#interactive"><span class=secno>3.18. </span>Interactive
      elements</a>
      <ul class=toc>
       <li><a href="#the-details"><span class=secno>3.18.1. </span>The
        <code>details</code> element</a>

       <li><a href="#datagrid"><span class=secno>3.18.2. </span>The
        <code>datagrid</code> element</a>
        <ul class=toc>
         <li><a href="#the-datagrid"><span class=secno>3.18.2.1. </span>The
          <code>datagrid</code> data model</a>

         <li><a href="#how-rows"><span class=secno>3.18.2.2. </span>How rows
          are identified</a>

         <li><a href="#the-data"><span class=secno>3.18.2.3. </span>The data
          provider interface</a>

         <li><a href="#the-default"><span class=secno>3.18.2.4. </span>The
          default data provider</a>
          <ul class=toc>
           <li><a href="#commonDefaultDataGridMethodDefinitions"><span
            class=secno>3.18.2.4.1. </span>Common default data provider
            method definitions for cells</a>
          </ul>

         <li><a href="#populating"><span class=secno>3.18.2.5.
          </span>Populating the <code>datagrid</code> element</a>

         <li><a href="#updating"><span class=secno>3.18.2.6. </span>Updating
          the <code>datagrid</code></a>

         <li><a href="#requirements"><span class=secno>3.18.2.7.
          </span>Requirements for interactive user agents</a>

         <li><a href="#the-selection"><span class=secno>3.18.2.8. </span>The
          selection</a>

         <li><a href="#columns"><span class=secno>3.18.2.9. </span>Columns
          and captions</a>
        </ul>

       <li><a href="#the-command"><span class=secno>3.18.3. </span>The
        <code>command</code> element</a>

       <li><a href="#menus"><span class=secno>3.18.4. </span>The
        <code>menu</code> element</a>
        <ul class=toc>
         <li><a href="#menus-intro"><span class=secno>3.18.4.1.
          </span>Introduction</a>

         <li><a href="#building"><span class=secno>3.18.4.2. </span>Building
          menus</a>

         <li><a href="#context"><span class=secno>3.18.4.3. </span>Context
          menus</a>

         <li><a href="#toolbars"><span class=secno>3.18.4.4.
          </span>Toolbars</a>
        </ul>

       <li><a href="#commands"><span class=secno>3.18.5. </span>Commands</a>
        <ul class=toc>
         <li><a href="#using"><span class=secno>3.18.5.1. </span>Using the
          <code>a</code> element to define a command</a>

         <li><a href="#using0"><span class=secno>3.18.5.2. </span>Using the
          <code>button</code> element to define a command</a>

         <li><a href="#using1"><span class=secno>3.18.5.3. </span>Using the
          <code>input</code> element to define a command</a>

         <li><a href="#using2"><span class=secno>3.18.5.4. </span>Using the
          <code>option</code> element to define a command</a>

         <li><a href="#using3"><span class=secno>3.18.5.5. </span>Using the
          <code>command</code> element to define a command</a>
        </ul>
      </ul>

     <li><a href="#miscellaneous"><span class=secno>3.19.
      </span>Miscellaneous elements</a>
      <ul class=toc>
       <li><a href="#the-legend"><span class=secno>3.19.1. </span>The
        <code>legend</code> element</a>

       <li><a href="#the-div"><span class=secno>3.19.2. </span>The
        <code>div</code> element</a>
      </ul>
    </ul>

   <li><a href="#web-browsers"><span class=secno>4. </span>Web browsers</a>
    <ul class=toc>
     <li><a href="#windows"><span class=secno>4.1. </span>Browsing
      contexts</a>
      <ul class=toc>
       <li><a href="#nested"><span class=secno>4.1.1. </span>Nested browsing
        contexts</a>

       <li><a href="#auxiliary"><span class=secno>4.1.2. </span>Auxiliary
        browsing contexts</a>

       <li><a href="#secondary"><span class=secno>4.1.3. </span>Secondary
        browsing contexts</a>

       <li><a href="#threads"><span class=secno>4.1.4. </span>Threads</a>

       <li><a href="#browsing"><span class=secno>4.1.5. </span>Browsing
        context names</a>
      </ul>

     <li><a href="#the-default0"><span class=secno>4.2. </span>The default
      view</a>
      <ul class=toc>
       <li><a href="#security1"><span class=secno>4.2.1. </span>Security</a>

       <li><a href="#constructors"><span class=secno>4.2.2.
        </span>Constructors</a>

       <li><a href="#apis-for"><span class=secno>4.2.3. </span>APIs for
        creating and navigating browsing contexts by name</a>

       <li><a href="#accessing"><span class=secno>4.2.4. </span>Accessing
        other browsing contexts</a>
      </ul>

     <li><a href="#history"><span class=secno>4.3. </span>Session history and
      navigation</a>
      <ul class=toc>
       <li><a href="#the-session"><span class=secno>4.3.1. </span>The session
        history of browsing contexts</a>

       <li><a href="#the-history"><span class=secno>4.3.2. </span>The
        <code>History</code> interface</a>

       <li><a href="#activating"><span class=secno>4.3.3. </span>Activating
        state objects</a>

       <li><a href="#the-location"><span class=secno>4.3.4. </span>The
        <code>Location</code> interface</a>
        <ul class=toc>
         <li><a href="#security2"><span class=secno>4.3.4.1.
          </span>Security</a>
        </ul>

       <li><a href="#history-notes"><span class=secno>4.3.5.
        </span>Implementation notes for session history</a>
      </ul>

     <li><a href="#links"><span class=secno>4.4. </span>Links</a>
      <ul class=toc>
       <li><a href="#hyperlink"><span class=secno>4.4.1. </span>Hyperlink
        elements</a>

       <li><a href="#following"><span class=secno>4.4.2. </span>Following
        hyperlinks</a>
        <ul class=toc>
         <li><a href="#hyperlink0"><span class=secno>4.4.2.1.
          </span>Hyperlink auditing</a>
        </ul>

       <li><a href="#linkTypes"><span class=secno>4.4.3. </span>Link
        types</a>
        <ul class=toc>
         <li><a href="#link-type"><span class=secno>4.4.3.1. </span>Link type
          "<code>alternate</code>"</a>

         <li><a href="#link-type0"><span class=secno>4.4.3.2. </span>Link
          type "<code>archives</code>"</a>

         <li><a href="#link-type1"><span class=secno>4.4.3.3. </span>Link
          type "<code>author</code>"</a>

         <li><a href="#link-type2"><span class=secno>4.4.3.4. </span>Link
          type "<code>bookmark</code>"</a>

         <li><a href="#link-type3"><span class=secno>4.4.3.5. </span>Link
          type "<code>contact</code>"</a>

         <li><a href="#link-type4"><span class=secno>4.4.3.6. </span>Link
          type "<code>external</code>"</a>

         <li><a href="#link-type5"><span class=secno>4.4.3.7. </span>Link
          type "<code>feed</code>"</a>

         <li><a href="#link-type6"><span class=secno>4.4.3.8. </span>Link
          type "<code>help</code>"</a>

         <li><a href="#link-type7"><span class=secno>4.4.3.9. </span>Link
          type "<code>icon</code>"</a>

         <li><a href="#link-type8"><span class=secno>4.4.3.10. </span>Link
          type "<code>license</code>"</a>

         <li><a href="#link-type9"><span class=secno>4.4.3.11. </span>Link
          type "<code>nofollow</code>"</a>

         <li><a href="#link-type10"><span class=secno>4.4.3.12. </span>Link
          type "<code>pingback</code>"</a>

         <li><a href="#link-type11"><span class=secno>4.4.3.13. </span>Link
          type "<code>prefetch</code>"</a>

         <li><a href="#link-type12"><span class=secno>4.4.3.14. </span>Link
          type "<code>search</code>"</a>

         <li><a href="#link-type13"><span class=secno>4.4.3.15. </span>Link
          type "<code>stylesheet</code>"</a>

         <li><a href="#link-type14"><span class=secno>4.4.3.16. </span>Link
          type "<code>sidebar</code>"</a>

         <li><a href="#link-type15"><span class=secno>4.4.3.17. </span>Link
          type "<code>tag</code>"</a>

         <li><a href="#hierarchical"><span class=secno>4.4.3.18.
          </span>Hierarchical link types</a>
          <ul class=toc>
           <li><a href="#link-type16"><span class=secno>4.4.3.18.1.
            </span>Link type "<code>first</code>"</a>

           <li><a href="#link-type17"><span class=secno>4.4.3.18.2.
            </span>Link type "<code>index</code>"</a>

           <li><a href="#link-type18"><span class=secno>4.4.3.18.3.
            </span>Link type "<code>last</code>"</a>

           <li><a href="#link-type19"><span class=secno>4.4.3.18.4.
            </span>Link type "<code>next</code>"</a>

           <li><a href="#link-type20"><span class=secno>4.4.3.18.5.
            </span>Link type "<code>prev</code>"</a>

           <li><a href="#link-type21"><span class=secno>4.4.3.18.6.
            </span>Link type "<code>up</code>"</a>
          </ul>

         <li><a href="#other0"><span class=secno>4.4.3.19. </span>Other link
          types</a>
        </ul>
      </ul>

     <li><a href="#interfaces"><span class=secno>4.5. </span>Interfaces for
      URI manipulation</a>

     <li><a href="#navigating"><span class=secno>4.6. </span>Navigating
      across documents</a>
      <ul class=toc>
       <li><a href="#read-html"><span class=secno>4.6.1. </span>Page load
        processing model for HTML files</a>

       <li><a href="#read-xml"><span class=secno>4.6.2. </span>Page load
        processing model for XML files</a>

       <li><a href="#read-text"><span class=secno>4.6.3. </span>Page load
        processing model for text files</a>

       <li><a href="#read-image"><span class=secno>4.6.4. </span>Page load
        processing model for images</a>

       <li><a href="#read-plugin"><span class=secno>4.6.5. </span>Page load
        processing model for content that uses plugins</a>

       <li><a href="#non-DOM-inline-content"><span class=secno>4.6.6.
        </span>Page load processing model for inline content that doesn't
        have a DOM</a>

       <li><a href="#scroll-to-fragid"><span class=secno>4.6.7.
        </span>Scrolling to a fragment identifier</a>
      </ul>

     <li><a href="#content-type-sniffing"><span class=secno>4.7.
      </span>Determining the type of a new resource in a browsing context</a>
      
      <ul class=toc>
       <li><a href="#content-type0"><span class=secno>4.7.1.
        </span>Content-Type sniffing: text or binary</a>

       <li><a href="#content-type1"><span class=secno>4.7.2.
        </span>Content-Type sniffing: unknown type</a>

       <li><a href="#content-type2"><span class=secno>4.7.3.
        </span>Content-Type sniffing: image</a>

       <li><a href="#content-type3"><span class=secno>4.7.4.
        </span>Content-Type sniffing: feed or HTML</a>

       <li><a href="#content-type"><span class=secno>4.7.5.
        </span>Content-Type metadata</a>
      </ul>

     <li><a href="#user-prompts"><span class=secno>4.8. </span>User
      prompts</a>

     <li><a href="#scripting"><span class=secno>4.9. </span>Scripting</a>
      <ul class=toc>
       <li><a href="#running"><span class=secno>4.9.1. </span>Running
        executable code</a>

       <li><a href="#origin"><span class=secno>4.9.2. </span>Origin</a>

       <li><a href="#security3"><span class=secno>4.9.3. </span>Security
        exceptions</a>

       <li><a href="#javascript-protocol"><span class=secno>4.9.4. </span>The
        <code title="">javascript:</code> protocol</a>

       <li><a href="#events"><span class=secno>4.9.5. </span>Events</a>
        <ul class=toc>
         <li><a href="#event-handler-attributes"><span class=secno>4.9.5.1.
          </span>Event handler attributes</a>

         <li><a href="#event"><span class=secno>4.9.5.2. </span>Event
          firing</a>

         <li><a href="#events0"><span class=secno>4.9.5.3. </span>Events and
          the <code>Window</code> object</a>

         <li><a href="#runtime-script-errors"><span class=secno>4.9.5.4.
          </span>Runtime script errors</a>
        </ul>
      </ul>

     <li><a href="#browser"><span class=secno>4.10. </span>Browser state</a>
      <ul class=toc>
       <li><a href="#offline"><span class=secno>4.10.1. </span>Offline Web
        applications</a>

       <li><a href="#custom-handlers"><span class=secno>4.10.2. </span>Custom
        protocol and content handlers</a>
        <ul class=toc>
         <li><a href="#security4"><span class=secno>4.10.2.1. </span>Security
          and privacy</a>

         <li><a href="#sample-handler-impl"><span class=secno>4.10.2.2.
          </span>Sample user interface</a>
        </ul>
      </ul>

     <li><a href="#storage"><span class=secno>4.11. </span>Client-side
      session and persistent storage of name/value pairs</a>
      <ul class=toc>
       <li><a href="#introduction0"><span class=secno>4.11.1.
        </span>Introduction</a>

       <li><a href="#the-storage"><span class=secno>4.11.2. </span>The
        <code>Storage</code> interface</a>

       <li><a href="#the-storageitem"><span class=secno>4.11.3. </span>The
        <code>StorageItem</code> interface</a>

       <li><a href="#the-sessionstorage"><span class=secno>4.11.4. </span>The
        <code title=dom-sessionStorage>sessionStorage</code> attribute</a>

       <li><a href="#the-globalstorage"><span class=secno>4.11.5. </span>The
        <code title=dom-globalStorage>globalStorage</code> attribute</a>

       <li><a href="#the-storage0"><span class=secno>4.11.6. </span>The <code
        title=event-storage>storage</code> event</a>

       <li><a href="#miscellaneous0"><span class=secno>4.11.7.
        </span>Miscellaneous implementation requirements for storage
        areas</a>
        <ul class=toc>
         <li><a href="#disk-space"><span class=secno>4.11.7.1. </span>Disk
          space</a>

         <li><a href="#threads0"><span class=secno>4.11.7.2.
          </span>Threads</a>
        </ul>

       <li><a href="#security5"><span class=secno>4.11.8. </span>Security and
        privacy</a>
        <ul class=toc>
         <li><a href="#user-tracking"><span class=secno>4.11.8.1. </span>User
          tracking</a>

         <li><a href="#cookie"><span class=secno>4.11.8.2. </span>Cookie
          resurrection</a>

         <li><a href="#integrity"><span class=secno>4.11.8.3.
          </span>Integrity of "public" storage areas</a>

         <li><a href="#cross-protocol"><span class=secno>4.11.8.4.
          </span>Cross-protocol and cross-port attacks</a>

         <li><a href="#dns-spoofing"><span class=secno>4.11.8.5. </span>DNS
          spoofing attacks</a>

         <li><a href="#cross-directory"><span class=secno>4.11.8.6.
          </span>Cross-directory attacks</a>

         <li><a href="#public"><span class=secno>4.11.8.7. </span>Public
          storage areas corresponding to hosts</a>

         <li><a href="#storage0"><span class=secno>4.11.8.8. </span>Storage
          areas in the face of untrusted higher-level domains that do not
          correspond to public storage areas</a>

         <li><a href="#storage1"><span class=secno>4.11.8.9. </span>Storage
          areas in the face of untrusted subdomains</a>

         <li><a href="#implementation"><span class=secno>4.11.8.10.
          </span>Implementation risks</a>
        </ul>
      </ul>

     <li><a href="#sql"><span class=secno>4.12. </span>Client-side database
      storage</a>
      <ul class=toc>
       <li><a href="#introduction1"><span class=secno>4.12.1.
        </span>Introduction</a>

       <li><a href="#executing"><span class=secno>4.12.2. </span>Executing
        SQL statements</a>

       <li><a href="#database"><span class=secno>4.12.3. </span>Database
        query results</a>

       <li><a href="#privacy"><span class=secno>4.12.4. </span>Privacy</a>

       <li><a href="#security6"><span class=secno>4.12.5. </span>Security</a>
        
        <ul class=toc>
         <li><a href="#user-agents"><span class=secno>4.12.5.1. </span>User
          agents</a>

         <li><a href="#sql-injection"><span class=secno>4.12.5.2. </span>SQL
          injection</a>
        </ul>
      </ul>
    </ul>

   <li><a href="#editing"><span class=secno>5. </span>Editing</a>
    <ul class=toc>
     <li><a href="#editing-intro"><span class=secno>5.1.
      </span>Introduction</a>

     <li><a href="#contenteditable"><span class=secno>5.2. </span>The <code
      title=attr-contenteditable>contenteditable</code> attribute</a>
      <ul class=toc>
       <li><a href="#user-editing"><span class=secno>5.2.1. </span>User
        editing actions</a>

       <li><a href="#making"><span class=secno>5.2.2. </span>Making entire
        documents editable</a>
      </ul>

     <li><a href="#dnd"><span class=secno>5.3. </span>Drag and drop</a>
      <ul class=toc>
       <li><a href="#the-dragevent"><span class=secno>5.3.1. </span>The
        <code>DragEvent</code> and <code>DataTransfer</code> interfaces</a>

       <li><a href="#events1"><span class=secno>5.3.2. </span>Events fired
        during a drag-and-drop action</a>

       <li><a href="#drag-and-drop"><span class=secno>5.3.3.
        </span>Drag-and-drop processing model</a>
        <ul class=toc>
         <li><a href="#when-the"><span class=secno>5.3.3.1. </span>When the
          drag-and-drop operation starts or ends in another document</a>

         <li><a href="#when-the0"><span class=secno>5.3.3.2. </span>When the
          drag-and-drop operation starts or ends in another application</a>
        </ul>

       <li><a href="#the-draggable"><span class=secno>5.3.4. </span>The
        <code>draggable</code> attribute</a>

       <li><a href="#copy-and"><span class=secno>5.3.5. </span>Copy and
        paste</a>
        <ul class=toc>
         <li><a href="#copy-to"><span class=secno>5.3.5.1. </span>Copy to
          clipboard</a>

         <li><a href="#cut-to"><span class=secno>5.3.5.2. </span>Cut to
          clipboard</a>

         <li><a href="#paste"><span class=secno>5.3.5.3. </span>Paste from
          clipboard</a>

         <li><a href="#paste0"><span class=secno>5.3.5.4. </span>Paste from
          selection</a>
        </ul>

       <li><a href="#security7"><span class=secno>5.3.6. </span>Security
        risks in the drag-and-drop model</a>
      </ul>

     <li><a href="#undo"><span class=secno>5.4. </span>Undo history</a>
      <ul class=toc>
       <li><a href="#the-undomanager"><span class=secno>5.4.1. </span>The
        <code>UndoManager</code> interface</a>

       <li><a href="#undo-moving"><span class=secno>5.4.2. </span>Undo:
        moving back in the undo transaction history</a>

       <li><a href="#redo-moving"><span class=secno>5.4.3. </span>Redo:
        moving forward in the undo transaction history</a>

       <li><a href="#the-undomanagerevent"><span class=secno>5.4.4.
        </span>The <code>UndoManagerEvent</code> interface and the <code
        title=event-undo>undo</code> and <code title=event-redo>redo</code>
        events</a>

       <li><a href="#implementation0"><span class=secno>5.4.5.
        </span>Implementation notes</a>
      </ul>

     <li><a href="#command"><span class=secno>5.5. </span>Command APIs</a>

     <li><a href="#selection"><span class=secno>5.6. </span>The text
      selection APIs</a>
      <ul class=toc>
       <li><a href="#documentSelection"><span class=secno>5.6.1. </span>APIs
        for the browsing context selection</a>

       <li><a href="#textFieldSelection"><span class=secno>5.6.2. </span>APIs
        for the text field selections</a>
      </ul>
    </ul>

   <li><a href="#comms"><span class=secno>6. </span>Communication</a>
    <ul class=toc>
     <li><a href="#event0"><span class=secno>6.1. </span>Event
      definitions</a>

     <li><a href="#server-sent-events"><span class=secno>6.2.
      </span>Server-sent DOM events</a>
      <ul class=toc>
       <li><a href="#the-remoteeventtarget"><span class=secno>6.2.1.
        </span>The <code>RemoteEventTarget</code> interface</a>

       <li><a href="#connecting"><span class=secno>6.2.2. </span>Connecting
        to an event stream</a>

       <li><a href="#parsing0"><span class=secno>6.2.3. </span>Parsing an
        event stream</a>

       <li><a href="#event-stream-interpretation"><span class=secno>6.2.4.
        </span>Interpreting an event stream</a>

       <li><a href="#notes"><span class=secno>6.2.5. </span>Notes</a>
      </ul>

     <li><a href="#network"><span class=secno>6.3. </span>Network
      connections</a>
      <ul class=toc>
       <li><a href="#network-intro"><span class=secno>6.3.1.
        </span>Introduction</a>

       <li><a href="#the-connection"><span class=secno>6.3.2. </span>The
        <code>Connection</code> interface</a>

       <li><a href="#connection"><span class=secno>6.3.3. </span>Connection
        Events</a>

       <li><a href="#tcp-connections"><span class=secno>6.3.4. </span>TCP
        connections</a>

       <li><a href="#broadcast"><span class=secno>6.3.5. </span>Broadcast
        connections</a>
        <ul class=toc>
         <li><a href="#broadcasting"><span class=secno>6.3.5.1.
          </span>Broadcasting over TCP/IP</a>

         <li><a href="#bluetooth-broadcast"><span class=secno>6.3.5.2.
          </span>Broadcasting over Bluetooth</a>

         <li><a href="#irda-broadcast"><span class=secno>6.3.5.3.
          </span>Broadcasting over IrDA</a>
        </ul>

       <li><a href="#peer-to-peer"><span class=secno>6.3.6.
        </span>Peer-to-peer connections</a>
        <ul class=toc>
         <li><a href="#peer-to-peer0"><span class=secno>6.3.6.1.
          </span>Peer-to-peer connections over TCP/IP</a>

         <li><a href="#bluetooth-peer"><span class=secno>6.3.6.2.
          </span>Peer-to-peer connections over Bluetooth</a>

         <li><a href="#irda-peer"><span class=secno>6.3.6.3.
          </span>Peer-to-peer connections over IrDA</a>
        </ul>

       <li><a href="#the-common"><span class=secno>6.3.7. </span>The common
        protocol for TCP-based connections</a>
        <ul class=toc>
         <li><a href="#clients"><span class=secno>6.3.7.1. </span>Clients
          connecting over TCP</a>

         <li><a href="#servers"><span class=secno>6.3.7.2. </span>Servers
          accepting connections over TCP</a>

         <li><a href="#sending"><span class=secno>6.3.7.3. </span>Sending and
          receiving data over TCP</a>
        </ul>

       <li><a href="#network-security"><span class=secno>6.3.8.
        </span>Security</a>

       <li><a href="#network-other-specs"><span class=secno>6.3.9.
        </span>Relationship to other standards</a>
      </ul>

     <li><a href="#crossDocumentMessages"><span class=secno>6.4.
      </span>Cross-document messaging</a>
      <ul class=toc>
       <li><a href="#processing1"><span class=secno>6.4.1. </span>Processing
        model</a>
      </ul>
    </ul>

   <li><a href="#repetition"><span class=secno>7. </span>Repetition
    templates</a>

   <li><a href="#syntax"><span class=secno>8. </span>The HTML syntax</a>
    <ul class=toc>
     <li><a href="#writing"><span class=secno>8.1. </span>Writing HTML
      documents</a>
      <ul class=toc>
       <li><a href="#the-doctype"><span class=secno>8.1.1. </span>The
        DOCTYPE</a>

       <li><a href="#elements0"><span class=secno>8.1.2. </span>Elements</a>
        <ul class=toc>
         <li><a href="#start"><span class=secno>8.1.2.1. </span>Start
          tags</a>

         <li><a href="#end-tags"><span class=secno>8.1.2.2. </span>End
          tags</a>

         <li><a href="#attributes0"><span class=secno>8.1.2.3.
          </span>Attributes</a>

         <li><a href="#optional"><span class=secno>8.1.2.4. </span>Optional
          tags</a>

         <li><a href="#restrictions"><span class=secno>8.1.2.5.
          </span>Restrictions on content models</a>
        </ul>

       <li><a href="#text"><span class=secno>8.1.3. </span>Text</a>
        <ul class=toc>
         <li><a href="#newlines"><span class=secno>8.1.3.1.
          </span>Newlines</a>
        </ul>

       <li><a href="#character"><span class=secno>8.1.4. </span>Character
        entity references</a>

       <li><a href="#comments"><span class=secno>8.1.5. </span>Comments</a>
      </ul>

     <li><a href="#parsing"><span class=secno>8.2. </span>Parsing HTML
      documents</a>
      <ul class=toc>
       <li><a href="#overview"><span class=secno>8.2.1. </span>Overview of
        the parsing model</a>

       <li><a href="#the-input0"><span class=secno>8.2.2. </span>The input
        stream</a>

       <li><a href="#tokenisation"><span class=secno>8.2.3.
        </span>Tokenisation</a>
        <ul class=toc>
         <li><a href="#tokenising"><span class=secno>8.2.3.1.
          </span>Tokenising entities</a>
        </ul>

       <li><a href="#tree-construction"><span class=secno>8.2.4. </span>Tree
        construction</a>
        <ul class=toc>
         <li><a href="#the-initial"><span class=secno>8.2.4.1. </span>The
          initial phase</a>

         <li><a href="#the-root0"><span class=secno>8.2.4.2. </span>The root
          element phase</a>

         <li><a href="#the-main"><span class=secno>8.2.4.3. </span>The main
          phase</a>
          <ul class=toc>
           <li><a href="#the-stack"><span class=secno>8.2.4.3.1. </span>The
            stack of open elements</a>

           <li><a href="#the-list"><span class=secno>8.2.4.3.2. </span>The
            list of active formatting elements</a>

           <li><a href="#creating"><span class=secno>8.2.4.3.3.
            </span>Creating and inserting HTML elements</a>

           <li><a href="#closing"><span class=secno>8.2.4.3.4. </span>Closing
            elements that have implied end tags</a>

           <li><a href="#the-element"><span class=secno>8.2.4.3.5. </span>The
            element pointers</a>

           <li><a href="#the-insertion"><span class=secno>8.2.4.3.6.
            </span>The insertion mode</a>

           <li><a href="#how-to0"><span class=secno>8.2.4.3.7. </span>How to
            handle tokens in the main phase</a>
          </ul>

         <li><a href="#the-trailing"><span class=secno>8.2.4.4. </span>The
          trailing end phase</a>
        </ul>

       <li><a href="#the-end"><span class=secno>8.2.5. </span>The End</a>
      </ul>

     <li><a href="#namespaces"><span class=secno>8.3. </span>Namespaces</a>

     <li><a href="#entities"><span class=secno>8.4. </span>Entities</a>
    </ul>

   <li><a href="#wysiwyg"><span class=secno>9. </span>WYSIWYG editors</a>
    <ul class=toc>
     <li><a href="#presentational"><span class=secno>9.1.
      </span>Presentational markup</a>
      <ul class=toc>
       <li><a href="#wysiwyg0"><span class=secno>9.1.1. </span>WYSIWYG
        signature</a>

       <li><a href="#the-font"><span class=secno>9.1.2. </span>The
        <code>font</code> element</a>
      </ul>
    </ul>

   <li><a href="#rendering"><span class=secno>10. </span>Rendering</a>
    <ul class=toc>
     <li><a href="#rendering0"><span class=secno>10.1. </span>Rendering and
      the DOM</a>
    </ul>

   <li><a href="#no"><span class=secno>11. </span>Things that you can't do
    with this specification because they are better handled using other
    technologies that are further described herein</a>
    <ul class=toc>
     <li><a href="#localisation"><span class=secno>11.1.
      </span>Localisation</a>

     <li><a href="#declarative"><span class=secno>11.2. </span>Declarative 2D
      vector graphics and animation</a>

     <li><a href="#declarative0"><span class=secno>11.3. </span>Declarative
      3D scenes</a>

     <li><a href="#timers"><span class=secno>11.4. </span>Timers</a>

     <li><a href="#events2"><span class=secno>11.5. </span>Events</a>
    </ul>

   <li class=no-num><a href="#references">References</a>

   <li class=no-num><a href="#acknowledgements">Acknowledgements</a>
  </ul>
  <!--end-toc-->

  <hr>

  <h2 id=introduction><span class=secno>1. </span>Introduction</h2>

  <p><em>This section is non-normative.</em>

  <p>The World Wide Web's markup language has always been HTML. HTML was
   primarily designed as a language for semantically describing scientific
   documents, although its general design and adaptations over the years has
   enabled it to be used to describe a number of other types of documents.

  <p>The main area that has not been adequately addressed by HTML is a vague
   subject referred to as Web Applications. This specification attempts to
   rectify this, while at the same time updating the HTML specifications to
   address issues raised in the past few years.

  <h3 id=scope><span class=secno>1.1. </span>Scope</h3>

  <p><em>This section is non-normative.</em>

  <p>This specification is limited to providing a semantic-level markup
   language and associated semantic-level scripting APIs for authoring
   accessible pages on the Web ranging from static documents to dynamic
   applications.

  <p>The scope of this specification does not include addressing presentation
   concerns (although default rendering rules for Web browsers are included
   at the end of this specification).

  <p>The scope of this specification does not include documenting every HTML
   or DOM feature supported by Web browsers. Browsers support many features
   that are considered to be very bad for accessibility or that are otherwise
   inappropriate. For example, the <code>blink</code> element is clearly
   presentational and authors wishing to cause text to blink should instead
   use CSS.

  <p>The scope of this specification is not to describe an entire operating
   system. In particular, hardware configuration software, image manipulation
   tools, and applications that users would be expected to use with high-end
   workstations on a daily basis are out of scope. In terms of applications,
   this specification is targeted specifically at applications that would be
   expected to be used by users on an occasional basis, or regularly but from
   disparate locations, with low CPU requirements. For instance online
   purchasing systems, searching systems, games (especially multiplayer
   online games), public telephone books or address books, communications
   software (e-mail clients, instant messaging clients, discussion software),
   document editing software, etc.

  <p>For sophisticated cross-platform applications, there already exist
   several proprietary solutions (such as Mozilla's XUL and Macromedia's
   Flash). These solutions are evolving faster than any standards process
   could follow, and the requirements are evolving even faster. These systems
   are also significantly more complicated to specify, and are orders of
   magnitude more difficult to achieve interoperability with, than the
   solutions described in this document. Platform-specific solutions for such
   sophisticated applications (for example the MacOS X Core APIs) are even
   further ahead.

  <h4 id=relationship><span class=secno>1.1.1. </span>Relationship to HTML
   4.01, XHTML 1.1, DOM2 HTML</h4>

  <p><em>This section is non-normative.</em>

  <p>This specification represents a new version of HTML4 and XHTML1, along
   with a new version of the associated DOM2 HTML API. Migration from HTML4
   or XHTML1 to the format and APIs described in this specification should in
   most cases be straightforward, as care has been taken to ensure that
   backwards-compatibility is retained.</p>
  <!-- XXX refs -->

  <p>This specification will eventually supplant Web Forms 2.0 as well. <a
   href="#refsWF2">[WF2]</a>

  <h4 id=relationship0><span class=secno>1.1.2. </span>Relationship to XHTML2</h4>

  <p><em>This section is non-normative.</em>

  <p>XHTML2 <a href="#refsXHTML2">[XHTML2]</a> defines a new HTML vocabulary
   with better features for hyperlinks, multimedia content, annotating
   document edits, rich metadata, declarative interactive forms, and
   describing the semantics of human literary works such as poems and
   scientific papers.

  <p>However, it lacks elements to express the semantics of many of the
   non-document types of content often seen on the Web. For instance, forum
   sites, auction sites, search engines, online shops, and the like, do not
   fit the document metaphor well, and are not covered by XHTML2.

  <p><em>This</em> specification aims to extend HTML so that it is also
   suitable in these contexts.

  <p>XHTML2 and this specification use different namespaces and therefore can
   both be implemented in the same XML processor.

  <h4 id=relationship1><span class=secno>1.1.3. </span>Relationship to XUL,
   Flash, Silverlight, and other proprietary UI languages</h4>

  <p><em>This section is non-normative.</em>

  <p>This specification is independent of the various proprietary UI
   languages that various vendors provide. As an open, vender-neutral
   language, HTML provides for a solution to the same problems without the
   risk of vendor lock-in.

  <h3 id=structure><span class=secno>1.2. </span>Structure of this
   specification</h3>

  <p><em>This section is non-normative.</em>

  <p>This specification is divided into the following important sections:

  <dl>
   <dt><a href="#dom">The DOM</a>

   <dd>The DOM, or Document Object Model, provides a base for the rest of the
    specification.

   <dt><a href="#semantics">The Semantics</a>

   <dd>Documents are built from elements. These elements form a tree using
    the DOM. Each element also has a predefined meaning, which is explained
    in this section. User agent requirements for how to handle each element
    are also given, along with rules for authors on how to use the element.

   <dt><a href="#windows">Browsing Contexts</a>

   <dd>HTML documents do not exist in a vacuum &mdash; this section defines
    many of the features that affect environments that deal with multiple
    pages, links between pages, and running scripts.

   <dt>APIs

   <dd><a href="#editing">The Editing APIs</a>: HTML documents can provide a
    number of mechanisms for users to modify content, which are described in
    this section.

   <dd><a href="#comms">The Communication APIs</a>: Applications written in
    HTML often require mechanisms to communicate with remote servers, as well
    as communicating with other applications from different domains running
    on the same client.

   <dd><a href="#repetition">Repetition Templates</a>: A mechanism to support
    repeating sections in forms.

   <dt><a href="#syntax">The Language Syntax</a>

   <dd>All of these features would be for naught if they couldn't be
    represented in a serialised form and sent to other people, and so this
    section defines the syntax of HTML, along with rules for how to parse
    HTML.
  </dl>

  <p>There are also a couple of appendices, defining <a href="#wysiwyg">shims
   for WYSIWYG editors</a>, <a href="#rendering">rendering rules</a> for Web
   browsers, and listing <a href="#no">areas that are out of scope</a> for
   this specification.

  <h4 id=how-to><span class=secno>1.2.1. </span>How to read this
   specification</h4>

  <p>This specification should be read like all other specifications. First,
   it should be read cover-to-cover, multiple times. Then, it should be read
   backwards at least once. Then it should be read by picking random sections
   from the contents list and following all the cross-references.

  <h3 id=conformance><span class=secno>1.3. </span>Conformance requirements</h3>

  <p>All diagrams, examples, and notes in this specification are
   non-normative, as are all sections explicitly marked non-normative.
   Everything else in this specification is normative.

  <p>The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in the
   normative parts of this document are to be interpreted as described in
   RFC2119. For readability, these words do not appear in all uppercase
   letters in this specification. <a href="#refsRFC2119">[RFC2119]</a></p>
  <!-- XXX but they should be marked up -->

  <p>This specification describes the conformance criteria for user agents
   (relevant to implementors) and documents (relevant to authors and
   authoring tool implementors).

  <p class=note>There is no implied relationship between document conformance
   requirements and implementation conformance requirements. User agents are
   not free to handle non-conformant documents as they please; the processing
   model described in this specification applies to implementations
   regardless of the conformity of the input documents.</p>
  <!--XXX quite possible that
  this is stated twice. check for whether this is a dupe. -->

  <p>User agents fall into several (overlapping) categories with different
   conformance requirements.

  <dl>
   <dt id=interactive>Web browsers and other interactive user agents

   <dd>
    <p>Web browsers that support <a href="#xhtml5">XHTML</a> must process
     elements and attributes from the <a href="#html-namespace0">HTML
     namespace</a> found in <a href="#xml-documents">XML documents</a> as
     described in this specification, so that users can interact with them,
     unless the semantics of those elements have been overridden by other
     specifications.</p>

    <p class=example>A conforming XHTML processor would, upon finding an
     XHTML <code><a href="#script0">script</a></code> element in an XML
     document, execute the script contained in that element. However, if the
     element is found within an XSLT transformation sheet (assuming the UA
     also supports XSLT), then the processor would instead treat the <code><a
     href="#script0">script</a></code> element as an opaque element that
     forms part of the transform.</p>

    <p>Web browsers that support <a href="#html5" title=HTML5>HTML</a> must
     process documents labelled as <code>text/html</code> as described in
     this specification, so that users can interact with them.</p>

   <dt id=non-interactive>Non-interactive presentation user agents

   <dd>
    <p>User agents that process HTML and XHTML documents purely to render
     non-interactive versions of them must comply to the same conformance
     criteria as Web browsers, except that they are exempt from requirements
     regarding user interaction.</p>

    <p class=note>Typical examples of non-interactive presentation user
     agents are printers (static UAs) and overhead displays (dynamic UAs). It
     is expected that most static non-interactive presentation user agents
     will also opt to <a href="#non-scripted">lack scripting support</a>.</p>

    <p class=example>A non-interactive but dynamic presentation UA would
     still execute scripts, allowing forms to be dynamically submitted, and
     so forth. However, since the concept of "focus" is irrelevant when the
     user cannot interact with the document, the UA would not need to support
     any of the focus-related DOM APIs.</p>

   <dt><dfn id=non-scripted>User agents with no scripting support</dfn>

   <dd>
    <p>Implementations that do not support scripting (or which have their
     scripting features <a href="#scripting1" title="scripting is
     disabled">disabled</a>) are exempt from supporting the events and DOM
     interfaces mentioned in this specification. For the parts of this
     specification that are defined in terms of an events model or in terms
     of the DOM, such user agents must still act as if events and the DOM
     were supported.</p>

    <p class=note>Scripting can form an integral part of an application. Web
     browsers that do not support scripting, or that have scripting disabled,
     might be unable to fully convey the author's intent.</p>

   <dt>Conformance checkers

   <dd id=conformance-checkers>
    <p>Conformance checkers must verify that a document conforms to the
     applicable conformance criteria described in this specification.
     Conformance checkers are exempt from detecting errors that require
     interpretation of the author's intent (for example, while a document is
     non-conforming if the content of a <code><a
     href="#blockquote">blockquote</a></code> element is not a quote,
     conformance checkers do not have to check that <code><a
     href="#blockquote">blockquote</a></code> elements only contain quoted
     material).</p>

    <p>Conformance checkers must check that the input document conforms when
     <a href="#scripting1">scripting is disabled</a>, and should also check
     that the input document conforms when <a href="#scripting2">scripting is
     enabled</a>. (This is only a "SHOULD" and not a "MUST" requirement
     because it has been proven to be impossible. <a
     href="#refsHALTINGPROBLEM">[HALTINGPROBLEM]</a>)</p>
    <!-- XXX
    [Computable] On computable numbers, with an application to the
    Entscheidungsproblem. Alan M. Turing. In Proceedings of the London
    Mathematical Society, series 2, volume 42, pages 230-265. London
    Mathematical Society,
    1937. http://www.turingarchive.org/browse.php/B/12 (referenced:
    2007-03-03)
    -->
    
    <p>The term "HTML5 validator" can be used to refer to a conformance
     checker that itself conforms to the applicable requirements of this
     specification.</p>

    <div class=note>
     <p>XML DTDs cannot express all the conformance requirements of this
      specification. Therefore, a validating XML processor and a DTD cannot
      constitute a conformance checker. Also, since neither of the two
      authoring formats defined in this specification are applications of
      SGML, a validating SGML system cannot constitute a conformance checker
      either.</p>

     <p>To put it another way, there are three types of conformance criteria:</p>

     <ol>
      <li>Criteria that can be expressed in a DTD.

      <li>Criteria that cannot be expressed by a DTD, but can still be
       checked by a machine.

      <li>Criteria that can only be checked by a human.
     </ol>

     <p>A conformance checker must check for the first two. A simple
      DTD-based validator only checks for the first class of errors and is
      therefore not a conforming conformance checker according to this
      specification.</p>
    </div>

   <dt>Data mining tools

   <dd id=data-mining>
    <p>Applications and tools that process HTML and XHTML documents for
     reasons other than to either render the documents or check them for
     conformance should act in accordance to the semantics of the documents
     that they process.</p>

    <p class=example>A tool that generates <span title="sections and
     headings">document outlines</span> but increases the nesting level for
     each paragraph and does not increase the nesting level for each section
     would not be conforming.</p>

   <dt id=editors>Authoring tools and markup generators

   <dd>
    <p>Authoring tools and markup generators must generate conforming
     documents. Conformance criteria that apply to authors also apply to
     authoring tools, where appropriate.</p>

    <p>Authoring tools are exempt from the strict requirements of using
     elements only for their specified purpose, but only to the extent that
     authoring tools are not yet able to determine author intent.</p>

    <p class=example>For example, it is not conforming to use an <code><a
     href="#address">address</a></code> element for arbitrary contact
     information; that element can only be used for marking up contact
     information for the author of the document or section. However, since an
     authoring tools is likely unable to determine the difference, an
     authoring tool is exempt from that requirement.</p>

    <p class=note>In terms of conformance checking, an editor is therefore
     required to output documents that conform to the same extent that a
     conformance checker will verify.</p>

    <p>When an authoring tool is used to edit a non-conforming document, it
     may preserve the conformance errors in sections of the document that
     were not edited during the editing session (i.e. an editing tool is
     allowed to round-trip errorneous content). However, an authoring tool
     must not claim that the output is conformant if errors have been so
     preserved.</p>

    <p>Authoring tools are expected to come in two broad varieties: tools
     that work from structure or semantic data, and tools that work on a
     What-You-See-Is-What-You-Get media-specific editing basis (WYSIWYG).</p>

    <p>The former is the preferred mechanism for tools that author HTML,
     since the structure in the source information can be used to make
     informed choices regarding which HTML elements and attributes are most
     appropriate.</p>

    <p>However, WYSIWYG tools are legitimate, and this specification <a
     href="#wysiwyg1" title="WYSIWYG editors">makes certain concessions to
     WYSIWYG editors</a>.</p>

    <p>All authoring tools, whether WYSIWYG or not, should make a best effort
     attempt at enabling users to create well-structured, semantically rich,
     media-independent content.</p>
  </dl>

  <p>Some conformance requirements are phrased as requirements on elements,
   attributes, methods or objects. Such requirements fall into two
   categories; those describing content model restrictions, and those
   describing implementation behaviour. The former category of requirements
   are requirements on documents and authoring tools. The second category are
   requirements on user agents.

  <p>Conformance requirements phrased as algorithms or specific steps may be
   implemented in any manner, so long as the end result is equivalent. (In
   particular, the algorithms defined in this specification are intended to
   be easy to follow, and not intended to be performant.)

  <p id=hardwareLimitations>User agents may impose implementation-specific
   limits on otherwise unconstrained inputs, e.g. to prevent denial of
   service attacks, to guard against running out of memory, or to work around
   platform-specific limitations.

  <p>For compatibility with existing content and prior specifications, this
   specification describes two authoring formats: one based on XML (referred
   to as <dfn id=xhtml5 title=XHTML>XHTML5</dfn>), and one using a <a
   href="#parsing">custom format</a> inspired by SGML (referred to as <dfn
   id=html5>HTML5</dfn>). Implementations may support only one of these two
   formats, although supporting both is encouraged.

  <p id=authors-using-xhtml><a href="#xhtml5">XHTML</a> documents (<a
   href="#xml-documents">XML documents</a> using elements from the <a
   href="#html-namespace0">HTML namespace</a>) that use the new features
   described in this specification and that are served over the wire (e.g. by
   HTTP) must be sent using an XML MIME type such as
   <code>application/xml</code> or <code>application/xhtml+xml</code> and
   must not be served as <code>text/html</code>. <a
   href="#refsRFC3023">[RFC3023]</a>

  <p>Such XML documents may contain a <code>DOCTYPE</code> if desired, but
   this is not required to conform to this specification.

  <p class=note>According to the XML specification, XML processors are not
   guaranteed to process the external DTD subset referenced in the DOCTYPE.
   This means, for example, that using entities for characters in XHTML
   documents is unsafe (except for &amp;lt;, &amp;gt;, &amp;amp;, &amp;quot;
   and &amp;apos;). For interoperability, authors are advised to avoid
   optional features of XML.

  <p id=authors-using-html><a href="#html5" title=HTML5>HTML documents</a>,
   if they are served over the wire (e.g. by HTTP) must be labelled with the
   <code>text/html</code> MIME type.</p>
  <!--
  XXX update RFC 2854 -->

  <p id=entity-references>The language in this specification assumes that the
   user agent expands all entity references, and therefore does not include
   entity reference nodes in the DOM. If user agents do include entity
   reference nodes in the DOM, then user agents must handle them as if they
   were fully expanded when implementing this specification. For example, if
   a requirement talks about an element's child text nodes, then any text
   nodes that are children of an entity reference that is a child of that
   element would be used as well.</p>
  <!-- XXX unexpandable entities? -->

  <h4 id=common><span class=secno>1.3.1. </span>Common conformance
   requirements for APIs exposed to JavaScript</h4>

  <p class=big-issue>A lot of arrays/lists/<span>collection</span>s in this
   spec assume zero-based indexes but use the term "<var
   title="">index</var>th" liberally. We should define those to be zero-based
   and be clearer about this.

  <p>Unless other specified, if a DOM attribute that is a floating point
   number type (<code title="">float</code>) is assigned an Infinity or
   Not-a-Number value, a <code title=big-issue>NOT_SUPPORTED_ERR</code>
   exception must be raised.

  <p>Unless other specified, if a DOM attribute that is a signed numberic
   type is assigned a negative value, a <code
   title=big-issue>NOT_SUPPORTED_ERR</code> exception must be raised.

  <p>Unless other specified, if a method with an argument that is a floating
   point number type (<code title="">float</code>) is passed an Infinity or
   Not-a-Number value, a <code title=big-issue>NOT_SUPPORTED_ERR</code>
   exception must be raised.

  <p>Unless other specified, if a method is passed fewer arguments than is
   defined for that method in its IDL definition, a <code
   title=big-issue>NOT_SUPPORTED_ERR</code> exception must be raised.

  <p>Unless other specified, if a method is passed more arguments than is
   defined for that method in its IDL definition, the excess arguments must
   be ignored.

  <p>Unless other specified, if a method is expecting, as one of its
   arguments, as defined by its IDL definition, an object implementing a
   particular interface <var title="">X</var>, and the argument passed is an
   object whose [[Class]] property is neither that interface <var
   title="">X</var>, nor the name of an interface <var title="">Y</var> where
   this specification requires that all objects implementing interface <var
   title="">Y</var> also implement interface <var title="">X</var>, nor the
   name of an interface that inherits from the expected interface <var
   title="">X</var>, then a <code title="">TYPE_MISMATCH_ERR</code> exception
   must be raised.

  <p class=big-issue>Anything else? Passing the wrong type of object, maybe?
   Implied conversions to int/float?

  <h4 id=dependencies><span class=secno>1.3.2. </span>Dependencies</h4>

  <p>This specification relies on several other underlying specifications.

  <dl>
   <dt>XML

   <dd>
    <p>Implementations that support XHTML5 must support some version of XML,
     as well as its corresponding namespaces specification, because XHTML5
     uses an XML serialisation with namespaces. <a href="#refsXML">[XML]</a>
     <a href="#refsXMLNAMES">[XMLNAMES]</a></p>

   <dt>XML Base

   <dd>
    <p id=xmlBase>User agents must follow the rules given by XML Base to
     resolve relative URIs in HTML and XHTML fragments. That is the mechanism
     used in this specification for resolving relative URIs in DOM trees. <a
     href="#refsXMLBASE">[XMLBASE]</a></p>

    <p class=note>It is possible for <code
     title=attr-xml-base>xml:base</code> attributes to be present even in
     HTML fragments, as such attributes can be added dynamically using
     script.</p>

   <dt>DOM

   <dd>
    <p>Implementations must support some version of DOM Core and DOM Events,
     because this specification is defined in terms of the DOM, and some of
     the features are defined as extensions to the DOM Core interfaces. <a
     href="#refsDOM3CORE">[DOM3CORE]</a> <a
     href="#refsDOM3CORE">[DOM3EVENTS]</a></p>

   <dt>ECMAScript

   <dd>
    <p>Implementations that use ECMAScript to implement the APIs defined in
     this specification must implement them in a manner consistent with the
     ECMAScript Bindings for DOM Specifications specification, as this
     specification uses that specification's terminology. <a
     href="#refsEBFD">[EBFD]</a></p>
  </dl>

  <p>This specification does not require support of any particular network
   transport protocols, image formats, audio formats, video formats, style
   sheet language, scripting language, or any of the DOM and WebAPI
   specifications beyond those described above. However, the language
   described by this specification is biased towards CSS as the styling
   language, ECMAScript as the scripting language, and HTTP as the network
   protocol, and several features assume that those languages and protocols
   are in use.

  <h4 id=features><span class=secno>1.3.3. </span>Features defined in other
   specifications</h4>

  <p>Some elements are defined in terms of their DOM <dfn
   id=textcontent><code>textContent</code></dfn> attribute. This is an
   attribute defined on the <code>Node</code> interface in DOM3 Core. <a
   href="#refsDOM3CORE">[DOM3CORE]</a>

  <p class=big-issue>Should textContent be defined differently for dir="" and
   &lt;bdo>? Should we come up with an alternative to textContent that
   handles those and other things, like alt=""?</p>
  <!-- This section is currently here exclusively so that we crossref
  to textContent. XXX also add event-click, event-change,
  event-DOMActivate, etc, here, and just have the section be a general
  "defined in other specifications" section -->

  <p>The term <dfn id=activation0>activation behavior</dfn> is used as
   defined in the DOM3 Events specification. <a
   href="#refsDOM3EVENTS">[DOM3EVENTS]</a> <span class=big-issue>At the time
   of writing, DOM3 Events hadn't yet been updated to define that
   phrase.</span>

  <p id=alternate-style-sheets>The rules for handling alternative style
   sheets are defined in the CSS object model specification. <a
   href="#CSSOM">[CSSOM]</a>

  <p class=big-issue>See <a
   href="http://dev.w3.org/cvsweb/~checkout~/csswg/cssom/Overview.html?rev=1.35&amp;content-type=text/html;%20charset=utf-8">http://dev.w3.org/cvsweb/~checkout~/csswg/cssom/Overview.html?rev=1.35&amp;content-type=text/html;%20charset=utf-8</a>

  <p>Certain features are defined in terms of CSS &lt;color&gt; values. When
   the CSS value <code title="">currentColor</code> is specified in this
   context, the "computed value of the 'color' property" for the purposes of
   determining the computed value of the <code title="">currentColor</code>
   keyword is the computed value of the 'color' property on the element in
   question. <a href="#refsCSS3COLOR">[CSS3COLOR]</a>

  <p class=example>If a canvas gradient's <code
   title=dom-canvasgradient-addColorStop><a
   href="#addcolorstop">addColorStop()</a></code> method is called with the
   <code title="">currentColor</code> keyword as the color, then the computed
   value of the 'color' property on the <code><a
   href="#canvas">canvas</a></code> element is the one that is used.

  <h3 id=terminology><span class=secno>1.4. </span>Terminology</h3>

  <p>This specification refers to both HTML and XML attributes and DOM
   attributes, often in the same context. When it is not clear which is being
   referred to, they are referred to as <dfn id=content>content
   attributes</dfn> for HTML and XML attributes, and <dfn
   id=dom-attributes>DOM attributes</dfn> for those from the DOM. Similarly,
   the term "properties" is used for both ECMAScript object properties and
   CSS properties. When these are ambiguous they are qualified as object
   properties and CSS properties respectively.

  <p id=html-namespace>To ease migration from HTML to XHTML, UAs conforming
   to this specification will place elements in HTML in the
   <code>http://www.w3.org/1999/xhtml</code> namespace, at least for the
   purposes of the DOM and CSS. The term "<dfn id=elements1>elements in the
   HTML namespace</dfn>", or "<dfn id=html-elements>HTML elements</dfn>" for
   short, when used in this specification, thus refers to both HTML and XHTML
   elements.

  <p>Unless otherwise stated, all elements defined or mentioned in this
   specification are in the <code>http://www.w3.org/1999/xhtml</code>
   namespace, and all attributes defined or mentioned in this specification
   have no namespace (they are in the per-element partition).

  <p>The term <a href="#html-">HTML documents</a> is sometimes used in
   contrast with <a href="#xml-documents">XML documents</a> to mean
   specifically documents that were parsed using an <a href="#html-0">HTML
   parser</a> (as opposed to using an XML parser or created purely through
   the DOM).

  <p>Generally, when the specification states that a feature applies to HTML
   or XHTML, it also includes the other. When a feature specifically only
   applies to one of the two languages, it is called out by explicitly
   stating that it does not apply to the other format, as in "for HTML, ...
   (this does not apply to XHTML)".

  <p>This specification uses the term <em>document</em> to refer to any use
   of HTML, ranging from short static documents to long essays or reports
   with rich multimedia, as well as to fully-fledged interactive
   applications.

  <p>For readability, the term URI is used to refer to both ASCII URIs and
   Unicode IRIs, as those terms are defined by <a
   href="#refsRFC3986">[RFC3986]</a> and <a href="#refsRFC3987">[RFC3987]</a>
   respectively. On the rare occasions where IRIs are not allowed but ASCII
   URIs are, this is called out explicitly.

  <p>The term <dfn id=root-element>root element</dfn>, when not qualified to
   explicitly refer to the document's root element, means the furthest
   ancestor element node of whatever node is being discussed, or the node
   itself is there is none. When the node is a part of the document, then
   that is indeed the document's root element. However, if the node is not
   currently part of the document tree, the root element will be an orphaned
   node.

  <p>An element is said to have been <dfn id=inserted title="insert an
   element into a document">inserted into a document</dfn> when its <a
   href="#root-element">root element</a> changes and is now the document's <a
   href="#root-element">root element</a>.

  <p>The term <dfn id=tree-order>tree order</dfn> means a pre-order,
   depth-first traversal of DOM nodes involved (through the <code
   title="">parentNode</code>/<code title="">childNodes</code> relationship).

  <p>When it is stated that some element or attribute is <dfn id=ignored
   title=ignore>ignored</dfn>, or treated as some other value, or handled as
   if it was something else, this refers only to the processing of the node
   after it is in the DOM. A user agent must not mutate the DOM in such
   situations.

  <p>When an XML name, such as an attribute or element name, is referred to
   in the form <code><var title="">prefix</var>:<var
   title="">localName</var></code>, as in <code>xml:id</code> or
   <code>svg:rect</code>, it refers to a name with the local name <var
   title="">localName</var> and the namespace given by the prefix, as defined
   by the following table:

  <dl>
   <dt><code title="">xml</code>

   <dd><code>http://www.w3.org/XML/1998/namespace</code>

   <dt><code title="">html</code>

   <dd><code>http://www.w3.org/1999/xhtml</code>

   <dt><code title="">svg</code>

   <dd><code>http://www.w3.org/2000/svg</code>
  </dl>

  <p>For simplicity, terms such as <em>shown</em>, <em>displayed</em>, and
   <em>visible</em> might sometimes be used when referring to the way a
   document is rendered to the user. These terms are not meant to imply a
   visual medium; they must be considered to apply to other media in
   equivalent ways.

  <p>Various DOM interfaces are defined in this specification using
   pseudo-IDL. This looks like OMG IDL but isn't. For instance, method
   overloading is used, and types from the W3C DOM specifications are used
   without qualification. Language-specific bindings for these abstract
   interface definitions must be derived in the way consistent with W3C DOM
   specifications. Some interface-specific binding information for ECMAScript
   is included in this specification.

  <p class=big-issue>The current situation with IDL blocks is pitiful. IDL is
   totally inadequate to properly represent what objects have to look like in
   JS; IDL can't say if a member is enumerable, what the indexing behaviour
   is, what the stringification behaviour is, what behaviour setting a member
   whose type is a particular interface should be (e.g. setting of
   document.location or element.className), what constructor an object
   implementing an interface should claim to have, how overloads work, etc. I
   think we should make the IDL blocks non-normative, and/or replace them
   with something else that is better for JS while still being clear on how
   it applies to other languages. However, we do need to have something that
   says what types the methods take as arguments, since we have to raise
   exceptions if they are wrong.

  <p>The construction "a <code>Foo</code> object", where <code>Foo</code> is
   actually an interface, is sometimes used instead of the more accurate "an
   object implementing the interface <code>Foo</code>".

  <p>A DOM attribute is said to be <em>getting</em> when its value is being
   retrieved (e.g. by author script), and is said to be <em>setting</em> when
   a new value is assigned to it.

  <p>If a DOM object is said to be <dfn id=live>live</dfn>, then that means
   that any attributes returning that object must always return the same
   object (not a new object each time), and the attributes and methods on
   that object must operate on the actual underlying data, not a snapshot of
   the data.</p>
  <!-- XXX should define "same instance of" to mean JS===. -->

  <p>The terms <em>fire</em> and <em>dispatch</em> are used interchangeably
   in the context of events, as in the DOM Events specifications. <a
   href="#refsDOM3EVENTS">[DOM3EVENTS]</a>

  <p>The term <dfn id=text-node>text node</dfn> refers to any
   <code>Text</code> node, including <code>CDATASection</code> nodes (any
   <code>Node</code> with node type 3 or 4).

  <p>Some of the algorithms in this specification, for historical reasons,
   require the user agent to <dfn id=pause>pause</dfn> until some condition
   has been met. While a user agent is paused, it must ensure that no scripts
   execute (e.g. no event handlers, no timers, etc). User agents should
   remain responsive to user input while paused, however.

  <h4 id=html-vs><span class=secno>1.4.1. </span>HTML vs XHTML</h4>

  <p><em>This section is non-normative.</em>

  <p>This specification defines an abstract language for describing documents
   and applications, and some APIs for interacting with in-memory
   representations of resources that use this language.

  <p>The in-memory representation is known as "DOM5 HTML", or "the DOM" for
   short.

  <p>There are various concrete syntaxes that can be used to transmit
   resources that use this abstract language, two of which are defined in
   this specification.

  <p>The first such concrete syntax is "HTML5". This is the format
   recommended for most authors. It is compatible with all legacy Web
   browsers. If a document is transmitted with the MIME type <code
   title="">text/html</code>, then it will be processed as an "HTML5"
   document by Web browsers.

  <p>The second concrete syntax uses XML, and is known as "XHTML5". When a
   document is transmitted with an XML MIME type, such as <code
   title="">application/xhtml+xml</code>, then it is processed by an XML
   processor by Web browsers, and treated as an "XHTML5" document. Generally
   speaking, authors are discouraged from trying to use XML on the Web,
   because XML has much stricter syntax rules than the "HTML5" variant
   described above, and is relatively newer and therefore less mature.

  <p>The "DOM5 HTML", "HTML5", and "XHTML5" representations cannot all
   represent the same content. For example, namespaces cannot be represented
   using "HTML5", but they are supported in "DOM5 HTML" and "XHTML5".
   Similarly, documents that use the <code><a
   href="#noscript">noscript</a></code> feature can be represented using
   "HTML5", but cannot be represented with "XHTML5" and "DOM5 HTML". Comments
   that contain the string "<code title="">--&gt;</code>" can be represented
   in "DOM5 HTML" but not in "HTML5" and "XHTML5". And so forth.

  <h2 id=dom><span class=secno>2. </span>The Document Object Model</h2>

  <p>The Document Object Model (DOM) is a representation &mdash; a model
   &mdash; of a document and its content. <a
   href="#refsDOM3CORE">[DOM3CORE]</a> The DOM is not just an API; the
   conformance criteria of HTML implementations are defined, in this
   specification, in terms of operations on the DOM.

  <p>This specification defines the language represented in the DOM by
   features together called DOM5 HTML. DOM5 HTML consists of DOM Core
   <code>Document</code> nodes and DOM Core <code>Element</code> nodes, along
   with text nodes and other content.

  <p>Elements in the DOM represent things; that is, they have intrinsic
   <em>meaning</em>, also known as semantics.

  <p class=example>For example, a <code><a href="#p">p</a></code> element
   represents a paragraph.

  <p>In addition, documents and elements in the DOM host APIs that extend the
   DOM Core APIs, providing new features to application developers using DOM5
   HTML.

  <h3 id=documents><span class=secno>2.1. </span>Documents</h3>

  <p>Every XML and HTML document in an HTML UA is represented by a
   <code>Document</code> object. <a href="#refsDOM3CORE">[DOM3CORE]</a>

  <p><code>Document</code> objects are assumed to be <dfn
   id=xml-documents>XML documents</dfn> unless they are flagged as being <dfn
   id=html->HTML documents</dfn> when they are created. Whether a document is
   an <a href="#html-" title="HTML documents">HTML document</a> or an <a
   href="#xml-documents" title="XML documents">XML document</a> affects the
   behaviour of certain APIs, as well as a few CSS rendering rules. <a
   href="#refsCSS21">[CSS21]</a>

  <p class=note>A <code>Document</code> object created by the <code
   title="">createDocument()</code> API on the <code>DOMImplementation</code>
   object is initially an <a href="#xml-documents" title="XML documents">XML
   document</a>, but can be made into an <a href="#html-" title="HTML
   documents">HTML document</a> by calling <code title=dom-document-open><a
   href="#open">document.open()</a></code> on it.

  <p>All <code>Document</code> objects (in user agents implementing this
   specification) must also implement the <code><a
   href="#htmldocument">HTMLDocument</a></code> interface, available using
   binding-specific methods. (This is the case whether or not the document in
   question is an <a href="#html-" title="HTML documents">HTML document</a>
   or indeed whether it contains any <a href="#html-elements">HTML
   elements</a> at all.) <code>Document</code> objects must also implement
   the document-level interface of any other namespaces found in the document
   that the UA supports. For example, if an HTML implementation also supports
   SVG, then the <code>Document</code> object must implement <code><a
   href="#htmldocument">HTMLDocument</a></code> and <code>SVGDocument</code>.

  <p class=note>Because the <code><a
   href="#htmldocument">HTMLDocument</a></code> interface is now obtained
   using binding-specific casting methods instead of simply being the primary
   interface of the document object, it is no longer defined as inheriting
   from <code>Document</code>.

  <pre class=idl>interface <dfn id=htmldocument>HTMLDocument</dfn> {
  // <a href="#resource0">Resource metadata management</a>
  readonly attribute <a href="#location2">Location</a> <a href="#location0" title=dom-document-location>location</a>;
  readonly attribute DOMString <a href="#url" title=dom-document-URL>URL</a>;
           attribute DOMString <a href="#domain" title=dom-document-domain>domain</a>;
  readonly attribute DOMString <a href="#referrer" title=dom-document-referrer>referrer</a>;
           attribute DOMString <a href="#cookie0" title=dom-document-cookie>cookie</a>;
  readonly attribute DOMString <a href="#lastmodified" title=dom-document-lastModified>lastModified</a>;

  // <a href="#dom-tree0">DOM tree accessors</a>
           attribute DOMString <a href="#document.title" title=dom-document-title>title</a>;
           attribute DOMString <a href="#dir1" title=dom-document-dir>dir</a>;
           attribute <a href="#htmlelement">HTMLElement</a> <a href="#body" title=dom-document-body>body</a>;
  readonly attribute <a href="#htmlcollection0">HTMLCollection</a> <a href="#images0" title=dom-document-images>images</a>;
<!--  readonly attribute <span>HTMLCollection</span> <span title="dom-document-applets">applets</span>;
-->  readonly attribute <a href="#htmlcollection0">HTMLCollection</a> <a href="#links0" title=dom-document-links>links</a>;
  readonly attribute <a href="#htmlcollection0">HTMLCollection</a> <a href="#forms0" title=dom-document-forms>forms</a>;
  readonly attribute <a href="#htmlcollection0">HTMLCollection</a> <a href="#anchors" title=dom-document-anchors>anchors</a>;
  NodeList <a href="#getelementsbyname" title=dom-document-getElementsByName>getElementsByName</a>(in DOMString elementName);
  NodeList <a href="#getelementsbyclassname" title=dom-document-getElementsByClassName>getElementsByClassName</a>(in DOMString[] classNames);

  // <a href="#dynamic2">Dynamic markup insertion</a>
           attribute DOMString <a href="#innerhtml" title=dom-innerHTML>innerHTML</a>;
  void <a href="#open" title=dom-document-open>open</a>();
  void <a href="#open" title=dom-document-open>open</a>(in DOMString type);
  void <a href="#open" title=dom-document-open>open</a>(in DOMString type, in DOMString replace);
  void <a href="#open" title=dom-document-open>open</a>(in DOMString url, in DOMString name, in DOMString features);
  void <a href="#open" title=dom-document-open>open</a>(in DOMString url, in DOMString name, in DOMString features, in bool replace);
  void <a href="#close" title=dom-document-close>close</a>();
  void <a href="#document.write" title=dom-document-write>write</a>(in DOMString text);
  void <a href="#document.writeln" title=dom-document-writeln>writeln</a>(in DOMString text);

  // <a href="#interaction0">Interaction</a>
  readonly attribute <span>Element</span> <a href="#activeelement" title=dom-document-activeElement>activeElement</a>;
  readonly attribute boolean <a href="#hasfocus" title=dom-document-hasFocus>hasFocus</a>;

  // <a href="#command1" title=concept-command>Commands</a>
  readonly attribute <a href="#htmlcollection0">HTMLCollection</a> <a href="#commands0" title=dom-document-commands>commands</a>;

  // <a href="#editing0">Editing</a>
           attribute boolean <a href="#designMode" title=dom-document-designMode>designMode</a>;
  boolean <a href="#execCommand" title=dom-document-execCommand>execCommand</a>(in DOMString commandId);
  boolean <a href="#execCommand" title=dom-document-execCommand>execCommand</a>(in DOMString commandId, in boolean doShowUI);
  boolean <a href="#execCommand" title=dom-document-execCommand>execCommand</a>(in DOMString commandId, in boolean doShowUI, in DOMString value);
  <a href="#selection1">Selection</a> <a href="#getselection0" title=dom-document-getSelection>getSelection</a>();

  // <a href="#cross-document">Cross-document messaging</a>
  void <a href="#postmessage" title=dom-document-postMessage>postMessage</a>(in DOMString message);
<!-- XXX we're not done here.
     XXX see e.g. http://lxr.mozilla.org/seamonkey/source/dom/public/idl/html/nsIDOMNSHTMLDocument.idl 
     XXX see e.g. http://trac.webkit.org/projects/webkit/browser/trunk/WebCore/dom/Document.cpp 
     XXX see e.g. http://trac.webkit.org/projects/webkit/browser/trunk/WebCore/html/HTMLDocument.cpp
  -->
};</pre>

  <p>Since the <code><a href="#htmldocument">HTMLDocument</a></code>
   interface holds methods and attributes related to a number of disparate
   features, the members of this interface are described in various different
   sections.

  <h4 id=security><span class=secno>2.1.1. </span>Security</h4>

  <p>User agents must raise a <a href="#security8">security exception</a>
   whenever any of the members of an <code><a
   href="#htmldocument">HTMLDocument</a></code> object are accessed by
   scripts whose <a href="#origin0">origin</a> is not the same as the
   <code>Document</code>'s origin, with the following exceptions:

  <ul>
   <li>The <code title=dom-document-postMessage><a
    href="#postmessage">postMessage()</a></code> method must be allowed to be
    called from any script.
  </ul>

  <p class=big-issue>We may want to just put postMessage on Window instead of
   Document, as that reduces the XSS risk.

  <h4 id=resource><span class=secno>2.1.2. </span><dfn id=resource0>Resource
   metadata management</dfn></h4>

  <p>The <dfn id=url title=dom-document-URL><code>URL</code></dfn> attribute
   must return <span>the document's address</span><!-- XXX
  xref -->.

  <p>The <dfn id=domain title=dom-document-domain><code>domain</code></dfn>
   attribute must be initialised to <span>the document's domain</span>, if it
   has one, and null otherwise. On getting, the attribute must return its
   current value. On setting, if the new value is an allowed value (as
   defined below), the attribute's value must be changed to the new value. If
   the new value is not an allowed value, then a <a
   href="#security8">security exception</a> must be raised instead.

  <p>A new value is an allowed value for the <code
   title=dom-document-domain><a href="#domain">document.domain</a></code>
   attribute if it is equal to the attribute's current value, or if the new
   value, prefixed by a U+002E FULL STOP ("."), exactly matches the end of
   the current value. If the current value is null, new values other than
   null will never be allowed.

  <p>If the <code>Document</code> object's <span title="the document's
   address">address</span><!-- XXX xref --> is hierarchical and uses a
   server-based naming authority, then its <dfn id=domain0 title="document's
   domain">domain</dfn> is the &lt;hostname&gt; part of that address.
   Otherwise, it has no domain.

  <p class=note>The <code title=dom-document-domain><a
   href="#domain">domain</a></code> attribute is used to enable pages on
   different hosts of a domain to access each others' DOMs<span
   class=big-issue>, though this is not yet defined by this
   specification</span>.</p>
  <!-- XXX xref -->
  <!--XXX
    http://lxr.mozilla.org/seamonkey/source/content/html/document/src/nsHTMLDocument.cpp
    search for ::GetDomain ::SetDomain
    http://trac.webkit.org/projects/webkit/browser/trunk/WebCore/dom/Document.cpp
    search for ::domain ::setDomain
  -->

  <p>The <dfn id=referrer
   title=dom-document-referrer><code>referrer</code></dfn> attribute must
   return either the URI of the page which <a href="#navigate"
   title=navigate>navigated</a> the <a href="#browsing0">browsing context</a>
   to the current document (if any), or the empty string (if there is no such
   originating page, or if the UA has been configured not to report
   referrers).

  <p class=note>In the case of HTTP, the <code title=dom-document-referrer><a
   href="#referrer">referrer</a></code> DOM attribute will match the
   <code>Referer</code> (sic) header that was sent when fetching the current
   page.

  <p>The <dfn id=cookie0 title=dom-document-cookie><code>cookie</code></dfn>
   attribute must, on getting, return the same string as the value of the
   <code title="">Cookie</code> HTTP header it would include if fetching the
   resource indicated by <span>the document's address</span> over HTTP, as
   per RFC 2109 section 4.3.4. <a href="#refsRFC2109">[RFC2109]</a>

  <p>On setting, the <code title=dom-document-cookie><a
   href="#cookie0">cookie</a></code> attribute must cause the user agent to
   act as it would when processing cookies if it had just attempted to fetch
   <span>the document's address</span> over HTTP, and had received a response
   with a <code>Set-Cookie</code> header whose value was the specified value,
   as per RFC 2109 sections 4.3.1, 4.3.2, and 4.3.3. <a
   href="#refsRFC2109">[RFC2109]</a>

  <p class=note>Since the <code title=dom-document-cookie><a
   href="#cookie0">cookie</a></code> attribute is accessible across frames,
   the path restrictions on cookies are only a tool to help manage which
   cookies are sent to which parts of the site, and are not in any way a
   security feature.

  <p>The <dfn id=lastmodified
   title=dom-document-lastModified><code>lastModified</code></dfn> attribute,
   on getting, must return the date and time of the <code>Document</code>'s
   source file's last modification, in the user's local timezone, in the
   following format:

  <ol>
   <li> The month component of the date.

   <li> A U+002F SOLIDUS character ('/').

   <li> The day component of the date.

   <li> A U+002F SOLIDUS character ('/').

   <li> The last two digits of the year component of the date.

   <li> A U+0020 SPACE character.

   <li> The hours component of the time.

   <li> A U+003A COLON character (':').

   <li> The minutes component of the time.

   <li> A U+003A COLON character (':').

   <li> The seconds component of the time.
  </ol>

  <p>All the numeric components above must be given as two digits in the
   range U+0030 DIGIT ZERO to U+0039 DIGIT NINE representing the number in
   base ten, zero-padded if necessary.

  <p>The <code>Document</code>'s source file's last modification date and
   time must be derived from relevant features of the networking protocols
   used, e.g. from the value of the HTTP <code title="">Last-Modified</code>
   header of the document, or from metadata in the filesystem for local
   files. If the last modification date and time are not known, the attribute
   must return the string <code title="">01/01/1970 00:00:00</code>.

  <h3 id=elements><span class=secno>2.2. </span>Elements</h3>

  <p>The nodes representing <a href="#html-elements">HTML elements</a> in the
   DOM must implement, and expose to scripts, the interfaces listed for them
   in the relevant sections of this specification. This includes <a
   href="#xhtml5">XHTML</a> elements in <a href="#xml-documents">XML
   documents</a>, even when those documents are in another context (e.g.
   inside an XSLT transform).

  <p>The basic interface, from which all the <a href="#html-elements">HTML
   elements</a>' interfaces inherit, and which must be used by elements that
   have no additional requirements, is the <code><a
   href="#htmlelement">HTMLElement</a></code> interface.

  <pre
   class=idl>interface <dfn id=htmlelement>HTMLElement</dfn> : <span>Element</span> {
  // <a href="#dom-tree0">DOM tree accessors</a>
  NodeList <a href="#getelementsbyclassname0" title=dom-getElementsByClassName>getElementsByClassName</a>(in DOMString[] classNames);

  // <a href="#dynamic2">Dynamic markup insertion</a>
           attribute DOMString <a href="#innerhtml" title=dom-innerHTML>innerHTML</a>;

  // <span>Metadata attributes</span>
           attribute DOMString <a href="#id0" title=dom-id>id</a>;
           attribute DOMString <a href="#title0" title=dom-title>title</a>;
           attribute DOMString <a href="#lang0" title=dom-lang>lang</a>;
           attribute DOMString <a href="#dir0" title=dom-dir>dir</a>;
           attribute <span>DOMString</span> <a href="#classname" title=dom-className>className</a>;
  readonly attribute <a href="#domtokenlist0">DOMTokenList</a> <a href="#classlist" title=dom-classList>classList</a>;

  // <a href="#interaction0">Interaction</a>
           attribute boolean <a href="#irrelevant0" title=dom-irrelevant>irrelevant</a>;
           attribute long <a href="#tabindex0" title=dom-tabindex>tabIndex</a>;
  void <a href="#click" title=dom-click>click</a>();
  void <a href="#focus0" title=dom-focus>focus</a>();
  void <a href="#blur" title=dom-blur>blur</a>();
  void <a href="#scrollintoview" title=dom-scrollIntoView>scrollIntoView</a>();
  void <a href="#scrollintoview" title=dom-scrollIntoView>scrollIntoView</a>(in boolean top);

  // <a href="#command1" title=concept-command>Commands</a>
           attribute <a href="#htmlmenuelement">HTMLMenuElement</a> <a href="#contextmenu0" title=dom-contextMenu>contextMenu</a>;

  // <a href="#editing0">Editing</a>
           attribute boolean <a href="#draggable0" title=dom-draggable>draggable</a>;
           attribute DOMString <a href="#contenteditable1" title=dom-contentEditable>contentEditable</a>;

  // <a href="#event3">event handler DOM attributes</a>
           attribute <span>EventListener</span> <a href="#onabort" title=handler-onabort>onabort</a>;
           attribute <span>EventListener</span> <a href="#onbeforeunload" title=handler-onbeforeunload>onbeforeunload</a>;
           attribute <span>EventListener</span> <a href="#onblur" title=handler-onblur>onblur</a>;
           attribute <span>EventListener</span> <a href="#onchange" title=handler-onchange>onchange</a>;
           attribute <span>EventListener</span> <a href="#onclick" title=handler-onclick>onclick</a>;
           attribute <span>EventListener</span> <a href="#oncontextmenu" title=handler-oncontextmenu>oncontextmenu</a>;
           attribute <span>EventListener</span> <a href="#ondblclick" title=handler-ondblclick>ondblclick</a>;
           attribute <span>EventListener</span> <a href="#ondrag" title=handler-ondrag>ondrag</a>;
           attribute <span>EventListener</span> <a href="#ondragend" title=handler-ondragend>ondragend</a>;
           attribute <span>EventListener</span> <a href="#ondragenter" title=handler-ondragenter>ondragenter</a>;
           attribute <span>EventListener</span> <a href="#ondragleave" title=handler-ondragleave>ondragleave</a>;
           attribute <span>EventListener</span> <a href="#ondragover" title=handler-ondragover>ondragover</a>;
           attribute <span>EventListener</span> <a href="#ondragstart" title=handler-ondragstart>ondragstart</a>;
           attribute <span>EventListener</span> <a href="#ondrop" title=handler-ondrop>ondrop</a>;
           attribute <span>EventListener</span> <a href="#onerror" title=handler-onerror>onerror</a>;
           attribute <span>EventListener</span> <a href="#onfocus" title=handler-onfocus>onfocus</a>;
           attribute <span>EventListener</span> <a href="#onkeydown" title=handler-onkeydown>onkeydown</a>;
           attribute <span>EventListener</span> <a href="#onkeypress" title=handler-onkeypress>onkeypress</a>;
           attribute <span>EventListener</span> <a href="#onkeyup" title=handler-onkeyup>onkeyup</a>;
           attribute <span>EventListener</span> <a href="#onload" title=handler-onload>onload</a>;
           attribute <span>EventListener</span> <a href="#onmessage" title=handler-onmessage>onmessage</a>;
           attribute <span>EventListener</span> <a href="#onmousedown" title=handler-onmousedown>onmousedown</a>;
           attribute <span>EventListener</span> <a href="#onmousemove" title=handler-onmousemove>onmousemove</a>;
           attribute <span>EventListener</span> <a href="#onmouseout" title=handler-onmouseout>onmouseout</a>;
           attribute <span>EventListener</span> <a href="#onmouseover" title=handler-onmouseover>onmouseover</a>;
           attribute <span>EventListener</span> <a href="#onmouseup" title=handler-onmouseup>onmouseup</a>;
           attribute <span>EventListener</span> <a href="#onmousewheel" title=handler-onmousewheel>onmousewheel</a>;
           attribute <span>EventListener</span> <a href="#onresize" title=handler-onresize>onresize</a>;
           attribute <span>EventListener</span> <a href="#onscroll" title=handler-onscroll>onscroll</a>;
           attribute <span>EventListener</span> <a href="#onselect" title=handler-onselect>onselect</a>;
           attribute <span>EventListener</span> <a href="#onsubmit" title=handler-onsubmit>onsubmit</a>;
           attribute <span>EventListener</span> <a href="#onunload" title=handler-onunload>onunload</a>;

};</pre>

  <p>As with the <code><a href="#htmldocument">HTMLDocument</a></code>
   interface, the <code><a href="#htmlelement">HTMLElement</a></code>
   interface holds methods and attributes related to a number of disparate
   features, and the members of this interface are therefore described in
   various different sections of this specification.

  <h4 id=reflecting><span class=secno>2.2.1. </span>Reflecting content
   attributes in DOM attributes</h4>

  <p>Some <span title="DOM attribute">DOM attributes</span> are defined to
   <dfn id=reflect>reflect</dfn> a particular <span>content attribute</span>.
   This means that on getting, the DOM attribute returns the current value of
   the content attribute, and on setting, the DOM attribute changes the value
   of the content attribute to the given value.

  <p>If a reflecting DOM attribute is a <code>DOMString</code> attribute
   whose content attribute is defined to contain a URI, then on getting, the
   DOM attribute must return the value of the content attribute, resolved to
   an absolute URI, and on setting, must set the content attribute to the
   specified literal value. If the content attribute is absent, the DOM
   attribute must return the default value, if the content attribute has one,
   or else the empty string.

  <p>If a reflecting DOM attribute is a <code>DOMString</code> whose content
   attribute is an <a href="#enumerated">enumerated attribute</a>, and the
   DOM attribute is <dfn id=limited>limited to only known values</dfn>, then,
   on getting, the DOM attribute must return the value associated with the
   state the attribute is in (in its canonical case), or the empty string if
   the attribute is in a state that has no associated keyword value; and on
   setting, if the new value case-insensitively matches one of the keywords
   given for that attribute, then the content attribute must be set to that
   value, otherwise, if the new value is the empty string, then the content
   attribute must be removed, otherwise, the setter must raise a
   <code>SYNTAX_ERR</code> exception.

  <p>If a reflecting DOM attribute is a <code>DOMString</code> but doesn't
   fall into any of the above categories, then the getting and setting must
   be done in a transparent, case-preserving manner.

  <p>If a reflecting DOM attribute is a boolean attribute, then the DOM
   attribute must return true if the attribute is set, and false if it is
   absent. On setting, the content attribute must be removed if the DOM
   attribute is set to false, and must be set to have the same value as its
   name if the DOM attribute is set to true. (This corresponds to the rules
   for <a href="#boolean0" title="boolean attribute">boolean content
   attributes</a>.)

  <p>If a reflecting DOM attribute is a signed integer type
   (<code>long</code>) then the content attribute must be parsed according to
   <a href="#rules0" title="rules for parsing integers">the rules for parsing
   signed integers</a> first. If that fails, or if the attribute is absent,
   the default value must be returned instead, or 0 if there is no default
   value. On setting, the given value must be converted to a string
   representing the number as a <a href="#valid0">valid integer</a> in base
   ten and then that string must be used as the new content attribute value.

  <p>If a reflecting DOM attribute is an <em>unsigned</em> integer type
   (<code>unsigned long</code>) then the content attribute must be parsed
   according to <a href="#rules" title="rules for parsing non-negative
   integers">the rules for parsing unsigned integers</a> first. If that
   fails, or if the attribute is absent, the default value must be returned
   instead, or 0 if there is no default value. On setting, the given value
   must be converted to a string representing the number as a <a
   href="#valid">valid non-negative integer</a> in base ten and then that
   string must be used as the new content attribute value.

  <p>If a reflecting DOM attribute is an unsigned integer type
   (<code>unsigned long</code>) that is <dfn id=limited0>limited to only
   positive non-zero numbers</dfn>, then the behavior is similar to the
   previous case, but zero is not allowed. On getting, the content attribute
   must first be parsed according to <a href="#rules" title="rules for
   parsing non-negative integers">the rules for parsing unsigned
   integers</a>, and if that fails, or if the attribute is absent, the
   default value must be returned instead, or 1 if there is no default value.
   On setting, if the value is zero, the user agent must fire an
   <code>INDEX_SIZE_ERR</code> exception. Otherwise, the given value must be
   converted to a string representing the number as a <a href="#valid">valid
   non-negative integer</a> in base ten and then that string must be used as
   the new content attribute value.

  <p>If a reflecting DOM attribute is a floating point number type
   (<code>float</code>) and the content attribute is defined to contain a
   time offset, then the content attribute must be parsed according to <a
   href="#rules4" title="rules for parsing time offsets">the rules for
   parsing time ofsets</a> first. If that fails, or if the attribute is
   absent, the default value must be returned instead, or the not-a-number
   value (NaN) if there is no default value. On setting, the given value must
   be converted to a string using the <a href="#time-offset">time offset
   serialisation rules</a>, and that string must be used as the new content
   attribute value.

  <p>If a reflecting DOM attribute is of the type <code><a
   href="#domtokenlist0">DOMTokenList</a></code>, then on getting it must
   return a <code><a href="#domtokenlist0">DOMTokenList</a></code> object
   whose underlying string is the element's corresponding content attribute.
   When the <code><a href="#domtokenlist0">DOMTokenList</a></code> object
   mutates its underlying string, the attribute must itself be immediately
   mutated. When the attribute is absent, then the string represented by the
   <code><a href="#domtokenlist0">DOMTokenList</a></code> object is the empty
   string; when the object mutates this empty string, the user agent must
   first add the corresponding content attribute, and then mutate that
   attribute instead. <code><a href="#domtokenlist0">DOMTokenList</a></code>
   attributes are always read-only. The same <code><a
   href="#domtokenlist0">DOMTokenList</a></code> object must be returned
   every time for each attribute.

  <p>If a reflecting DOM attribute has the type <code><a
   href="#htmlelement">HTMLElement</a></code>, or an interface that descends
   from <code><a href="#htmlelement">HTMLElement</a></code>, then, on
   getting, it must run the following algorithm (stopping at the first point
   where a value is returned):

  <ol>
   <li>If the corresponding content attribute is absent, then the DOM
    attribute must return null.

   <li>Let <var title="">candidate</var> be the element that the <code
    title="">document.getElementById()</code> method would find if it was
    passed as its argument the current value of the corresponding content
    attribute.

   <li>If <var title="">candidate</var> is null, or if it is not
    type-compatible with the DOM attribute, then the DOM attribute must
    return null.

   <li>Otherwise, it must return <var title="">candidate</var>.
  </ol>

  <p>On setting, if the given element has an <code title=attr-id><a
   href="#id">id</a></code> attribute, then the content attribute must be set
   to the value of that <code title=attr-id><a href="#id">id</a></code>
   attribute. Otherwise, the DOM attribute must be set to the empty string.</p>
  <!-- XXX or raise an exception? -->

  <h3 id=common0><span class=secno>2.3. </span>Common DOM interfaces</h3>

  <h4 id=collections><span class=secno>2.3.1. </span>Collections</h4>

  <p>The <code><a href="#htmlcollection0">HTMLCollection</a></code>, <code><a
   href="#htmlformcontrolscollection0">HTMLFormControlsCollection</a></code>,
   and <code><a
   href="#htmloptionscollection0">HTMLOptionsCollection</a></code> interfaces
   represent various lists of DOM nodes. Collectively, objects implementing
   these interfaces are called <dfn id=collections0>collections</dfn>.

  <p>When a <a href="#collections0" title=collections>collection</a> is
   created, a filter and a root are associated with the collection.

  <p class=example>For example, when the <code><a
   href="#htmlcollection0">HTMLCollection</a></code> object for the <code
   title=dom-document-images><a href="#images0">document.images</a></code>
   attribute is created, it is associated with a filter that selects only
   <code><a href="#img">img</a></code> elements, and rooted at the root of
   the document.

  <p>The <span>collection</span> then <dfn id=represents title="representated
   by the collection">represents</dfn> a <a href="#live">live</a> view of the
   subtree rooted at the collection's root, containing only nodes that match
   the given filter. The view is linear. In the absence of specific
   requirements to the contrary, the nodes within the collection must be
   sorted in <a href="#tree-order">tree order</a>.

  <p class=note>The <code title=dom-table-rows><a
   href="#rows">rows</a></code> list is not in tree order.

  <p>An attribute that returns a collection must return the same object every
   time it is retrieved.

  <h5 id=htmlcollection><span class=secno>2.3.1.1. </span>HTMLCollection</h5>

  <p>The <code><a href="#htmlcollection0">HTMLCollection</a></code> interface
   represents a generic <span>collection</span> of elements.

  <pre class=idl>interface <dfn id=htmlcollection0>HTMLCollection</dfn> {
  readonly attribute unsigned long <a href="#length" title=dom-HTMLCollection-length>length</a>;
  Element <a href="#itemindex" title=dom-HTMLCollection-item>item</a>(in unsigned long index);
  Element <a href="#nameditem" title=dom-HTMLCollection-namedItem>namedItem</a>(in DOMString name);
};</pre>

  <p>The <dfn id=length
   title=dom-HTMLCollection-length><code>length</code></dfn> attribute must
   return the number of nodes <span>represented by the collection</span>.

  <p>The <dfn id=itemindex title=dom-HTMLCollection-item><code>item(<var
   title="">index</var>)</code></dfn> method must return the <var
   title="">index</var>th node in the collection. If there is no <var
   title="">index</var>th node in the collection, then the method must return
   null.

  <p>The <dfn id=nameditem
   title=dom-HTMLCollection-namedItem><code>namedItem(<var
   title="">key</var>)</code></dfn> method must return the first node in the
   collection that matches the following requirements:

  <ul>
   <li>It is an <code><a href="#a">a</a></code>, <code>applet</code>,
    <code><a href="#area">area</a></code>, <code>form</code>, <code><a
    href="#img">img</a></code>, or <code><a href="#object">object</a></code>
    element with a <code title=attr-name>name</code> attribute equal to <var
    title="">key</var>, or,

   <li>It is an HTML element of any kind with an <code title=attr-id><a
    href="#id">id</a></code> attribute equal to <var title="">key</var>.
    (Non-HTML elements, even if they have IDs, are not searched for the
    purposes of <code title=dom-HTMLCollection-namedItem><a
    href="#nameditem">namedItem()</a></code>.)
  </ul>

  <p>If no such elements are found, then the method must return null.

  <p>In ECMAScript implementations, objects that implement the <code><a
   href="#htmlcollection0">HTMLCollection</a></code> interface must also have
   a [[Get]] method that, when invoked with a property name that is a number,
   acts like the <code title=dom-HTMLCollection-item><a
   href="#itemindex">item()</a></code> method would when invoked with that
   argument, and when invoked with a property name that is a string, acts
   like the <code title=dom-HTMLCollection-namedItem><a
   href="#nameditem">namedItem()</a></code> method would when invoked with
   that argument.

  <h5 id=htmlformcontrolscollection><span class=secno>2.3.1.2.
   </span>HTMLFormControlsCollection</h5>

  <p>The <code><a
   href="#htmlformcontrolscollection0">HTMLFormControlsCollection</a></code>
   interface represents a <span>collection</span> of form controls.

  <pre
   class=idl>interface <dfn id=htmlformcontrolscollection0>HTMLFormControlsCollection</dfn> {
  readonly attribute unsigned long <a href="#length0" title=dom-HTMLFormControlsCollection-length>length</a>;
  <a href="#htmlelement">HTMLElement</a> <a href="#itemindex0" title=dom-HTMLFormControlsCollection-item>item</a>(in unsigned long index);
  Object <a href="#nameditem0" title=dom-HTMLFormControlsCollection-namedItem>namedItem</a>(in DOMString name);
};</pre>

  <p>The <dfn id=length0
   title=dom-HTMLFormControlsCollection-length><code>length</code></dfn>
   attribute must return the number of nodes <span>represented by the
   collection</span>.

  <p>The <dfn id=itemindex0
   title=dom-HTMLFormControlsCollection-item><code>item(<var
   title="">index</var>)</code></dfn> method must return the <var
   title="">index</var>th node in the collection. If there is no <var
   title="">index</var>th node in the collection, then the method must return
   null.

  <p>The <dfn id=nameditem0
   title=dom-HTMLFormControlsCollection-namedItem><code>namedItem(<var
   title="">key</var>)</code></dfn> method must act according to the
   following algorithm:

  <ol>
   <li>If, at the time the method is called, there is exactly one node in the
    collection that has either an <code title=attr-id><a
    href="#id">id</a></code> attribute or a <code title=attr-name>name</code>
    attribute equal to <var title="">key</var>, then return that node and
    stop the algorithm.

   <li>Otherwise, if there are no nodes in the collection that have either an
    <code title=attr-id><a href="#id">id</a></code> attribute or a <code
    title=attr-name>name</code> attribute equal to <var title="">key</var>,
    then return null and stop the algorithm.

   <li>Otherwise, create a <code>NodeList</code> object representing a live
    view of the <code><a
    href="#htmlformcontrolscollection0">HTMLFormControlsCollection</a></code>
    object, further filtered so that the only nodes in the
    <code>NodeList</code> object are those that have either an <code
    title=attr-id><a href="#id">id</a></code> attribute or a <code
    title=attr-name>name</code> attribute equal to <var title="">key</var>.
    The nodes in the <code>NodeList</code> object must be sorted in <a
    href="#tree-order">tree order</a>.

   <li>Return that <code>NodeList</code> object.
  </ol>

  <p>In the ECMAScript DOM binding, objects implementing the <code><a
   href="#htmlformcontrolscollection0">HTMLFormControlsCollection</a></code>
   interface must support being dereferenced using the square bracket
   notation, such that dereferencing with an integer index is equivalent to
   invoking the <code title=dom-HTMLFormControlsCollection-item><a
   href="#itemindex0">item()</a></code> method with that index, and such that
   dereferencing with a string index is equivalent to invoking the <code
   title=dom-HTMLFormControlsCollection-namedItem><a
   href="#nameditem0">namedItem()</a></code> method with that index.</p>
  <!--
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-->

  <h5 id=htmloptionscollection><span class=secno>2.3.1.3.
   </span>HTMLOptionsCollection</h5>

  <p>The <code><a
   href="#htmloptionscollection0">HTMLOptionsCollection</a></code> interface
   represents a list of <code>option</code> elements.

  <pre
   class=idl>interface <dfn id=htmloptionscollection0>HTMLOptionsCollection</dfn> {
           attribute unsigned long <a href="#length1" title=dom-HTMLOptionsCollection-length>length</a>;
  HTMLOptionElement <a href="#itemindex1" title=dom-HTMLOptionsCollection-item>item</a>(in unsigned long index);
  Object <a href="#nameditem1" title=dom-HTMLOptionsCollection-namedItem>namedItem</a>(in DOMString name);
};</pre>

  <p>On getting, the <dfn id=length1
   title=dom-HTMLOptionsCollection-length><code>length</code></dfn> attribute
   must return the number of nodes <span>represented by the
   collection</span>.

  <p>On setting, the behaviour depends on whether the new value is equal to,
   greater than, or less than the number of nodes <span>represented by the
   collection</span> at that time. If the number is the same, then setting
   the attribute must do nothing. If the new value is greater, then <var
   title="">n</var> new <code>option</code> elements with no attributes and
   no child nodes must be appended to the <code>select</code> element on
   which the <code><a
   href="#htmloptionscollection0">HTMLOptionsCollection</a></code> is rooted,
   where <var title="">n</var> is the difference between the two numbers (new
   value minus old value). If the new value is lower, then the last <var
   title="">n</var> nodes in the collection must be removed from their parent
   nodes, where <var title="">n</var> is the difference between the two
   numbers (old value minus new value).

  <p class=note>Setting <code title=dom-HTMLOptionsCollection-length><a
   href="#length1">length</a></code> never removes or adds any
   <code>optgroup</code> elements, and never adds new children to existing
   <code>optgroup</code> elements (though it can remove children from them).

  <p>The <dfn id=itemindex1
   title=dom-HTMLOptionsCollection-item><code>item(<var
   title="">index</var>)</code></dfn> method must return the <var
   title="">index</var>th node in the collection. If there is no <var
   title="">index</var>th node in the collection, then the method must return
   null.

  <p>The <dfn id=nameditem1
   title=dom-HTMLOptionsCollection-namedItem><code>namedItem(<var
   title="">key</var>)</code></dfn> method must act according to the
   following algorithm:

  <ol>
   <li>If, at the time the method is called, there is exactly one node in the
    collection that has either an <code title=attr-id><a
    href="#id">id</a></code> attribute or a <code title=attr-name>name</code>
    attribute equal to <var title="">key</var>, then return that node and
    stop the algorithm.

   <li>Otherwise, if there are no nodes in the collection that have either an
    <code title=attr-id><a href="#id">id</a></code> attribute or a <code
    title=attr-name>name</code> attribute equal to <var title="">key</var>,
    then return null and stop the algorithm.

   <li>Otherwise, create a <code>NodeList</code> object representing a live
    view of the <code><a
    href="#htmloptionscollection0">HTMLOptionsCollection</a></code> object,
    further filtered so that the only nodes in the <code>NodeList</code>
    object are those that have either an <code title=attr-id><a
    href="#id">id</a></code> attribute or a <code
    title=attr-option-name>name</code> attribute equal to <var
    title="">key</var>. The nodes in the <code>NodeList</code> object must be
    sorted in <a href="#tree-order">tree order</a>.

   <li>Return that <code>NodeList</code> object.
  </ol>

  <p>In the ECMAScript DOM binding, objects implementing the <code><a
   href="#htmloptionscollection0">HTMLOptionsCollection</a></code> interface
   must support being dereferenced using the square bracket notation, such
   that dereferencing with an integer index is equivalent to invoking the
   <code title=dom-HTMLOptionsCollection-item><a
   href="#itemindex1">item()</a></code> method with that index, and such that
   dereferencing with a string index is equivalent to invoking the <code
   title=dom-HTMLOptionsCollection-namedItem><a
   href="#nameditem1">namedItem()</a></code> method with that index.</p>
  <!-- see also http://ln.hixie.ch/?start=1161042744&count=1 -->

  <p class=big-issue>We may want to add <code>add()</code> and
   <code>remove()</code> methods here too because IE implements
   HTMLSelectElement and HTMLOptionsCollection on the same object, and so
   people use them almost interchangeably in the wild.

  <h4 id=domtokenlist><span class=secno>2.3.2. </span>DOMTokenList</h4>

  <p>The <code><a href="#domtokenlist0">DOMTokenList</a></code> interface
   represents an interface to an underlying string that consists of an <a
   href="#unordered">unordered set of space-separated tokens</a>.

  <p>Which string underlies a particular <code><a
   href="#domtokenlist0">DOMTokenList</a></code> object is defined when the
   object is created. It might be a content attribute (e.g. the string that
   underlies the <code title=dom-classList><a
   href="#classlist">classList</a></code> object is the <code
   title=attr-class><a href="#class">class</a></code> attribute), or it might
   be an anonymous string (e.g. when a <code><a
   href="#domtokenlist0">DOMTokenList</a></code> object is passed to an
   author-implemented callback in the <code><a
   href="#datagrid0">datagrid</a></code> APIs).

  <pre class=idl>interface <dfn id=domtokenlist0>DOMTokenList</dfn> {
  readonly attribute unsigned long <a href="#length2" title=dom-tokenlist-length>length</a>;
  DOMString <a href="#itemindex2" title=dom-tokenlist-item>item</a>(in unsigned long index);
  boolean <a href="#hastoken" title=dom-tokenlist-has>has</a>(in DOMString token);
  void <a href="#remove" title=dom-tokenlist-add>add</a>(in DOMString token);
  void <span title=dom-tokenlist-remove>remove</span>(in DOMString token);
  boolean <a href="#toggle" title=dom-tokenlist-toggle>toggle</a>(in DOMString token);
};</pre>

  <p>The <dfn id=length2 title=dom-tokenlist-length><code>length</code></dfn>
   attribute must return the number of <em>unique</em> tokens that result
   from <a href="#split" title="split a string on spaces">splitting the
   underlying string on spaces</a>.

  <p>The <dfn id=itemindex2 title=dom-tokenlist-item><code>item(<var
   title="">index</var>)</code></dfn> method must <a href="#split"
   title="split a string on spaces">split the underlying string on
   spaces</a>, sort the resulting list of tokens by Unicode
   codepoint<!-- XXX that's
  basically nonsense. What sort order do we want here? It should be
  the cheapest one possible that is well-defined for all Unicode. -->,
   remove exact duplicates, and then return the <var title="">index</var>th
   item in this list. If <var title="">index</var> is equal to or greater
   than the number of tokens, then the method must return null.

  <p>In ECMAScript implementations, objects that implement the <code><a
   href="#domtokenlist0">DOMTokenList</a></code> interface must also have a
   [[Get]] method that, when invoked with a property name that is a number,
   acts like the <code title=dom-tokenlist-item><a
   href="#itemindex2">item()</a></code> method would when invoked with that
   argument.

  <p>The <dfn id=hastoken title=dom-tokenlist-has><code>has(<var
   title="">token</var>)</code></dfn> method must run the following
   algorithm:

  <ol>
   <li>If the <var title="">token</var> argument contains any
    spaces<!-- XXX elaborate -->, then raise an
    <code>INVALID_CHARACTER_ERR</code> exception and stop the algorithm.

   <li>Otherwise, <a href="#split" title="split a string on spaces">split the
    underlying string on spaces</a> to get the list of tokens in the object's
    underlying string.

   <li>If the token indicated by <var title="">token</var> is one of the
    tokens in the object's underlying string then return true and stop this
    algorithm.

   <li>Otherwise, return false.
  </ol>

  <p>The <dfn id=addtoken title=dom-tokenlist-add><code>add(<var
   title="">token</var>)</code></dfn> method must run the following
   algorithm:

  <ol>
   <li>If the <var title="">token</var> argument contains any
    spaces<!-- XXX elaborate -->, then raise an
    <code>INVALID_CHARACTER_ERR</code> exception and stop the algorithm.

   <li>Otherwise, <a href="#split" title="split a string on spaces">split the
    underlying string on spaces</a> to get the list of tokens in the object's
    underlying string.

   <li>If the given <var title="">token</var> is already one of the tokens in
    the <code><a href="#domtokenlist0">DOMTokenList</a></code> object's
    underlying string then stop the algorithm.

   <li>Otherwise, if the last character of the <code><a
    href="#domtokenlist0">DOMTokenList</a></code> object's underlying string
    is not a <a href="#space">space character</a>, then append a U+0020 SPACE
    character to the end of that string.

   <li>Append the value of <var title="">token</var> to the end of the
    <code><a href="#domtokenlist0">DOMTokenList</a></code> object's
    underlying string.
  </ol>

  <p>The <dfn id=remove title=dom-tokenlist-add><code>remove(<var
   title="">token</var>)</code></dfn> method must run the following
   algorithm:

  <ol>
   <li>If the <var title="">token</var> argument contains any <a
    href="#space" title="space character">spaces</a>, then raise an
    <code>INVALID_CHARACTER_ERR</code> exception and stop the algorithm.

   <li>Otherwise, <a href="#remove0" title="remove a token from a
    string">remove the given <var title="">token</var> from the underlying
    string</a>.
  </ol>

  <p>The <dfn id=toggle title=dom-tokenlist-toggle><code>toggle(<var
   title="">token</var>)</code></dfn> method must run the following
   algorithm:

  <ol>
   <li>If the <var title="">token</var> argument contains any
    spaces<!-- XXX elaborate -->, then raise an
    <code>INVALID_CHARACTER_ERR</code> exception and stop the algorithm.

   <li>Otherwise, <a href="#split" title="split a string on spaces">split the
    underlying string on spaces</a> to get the list of tokens in the object's
    underlying string.

   <li>If the given <var title="">token</var> is already one of the tokens in
    the <code><a href="#domtokenlist0">DOMTokenList</a></code> object's
    underlying string then <a href="#remove0" title="remove a token from a
    string">remove the given <var title="">token</var> from the underlying
    string</a>, and stop the algorithm, returning false.

   <li>Otherwise, if the last character of the <code><a
    href="#domtokenlist0">DOMTokenList</a></code> object's underlying string
    is not a <a href="#space">space character</a>, then append a U+0020 SPACE
    character to the end of that string.

   <li>Append the value of <var title="">token</var> to the end of the
    <code><a href="#domtokenlist0">DOMTokenList</a></code> object's
    underlying string.

   <li>Return true.
  </ol>

  <p>In the ECMAScript DOM binding, objects implementing the <code><a
   href="#domtokenlist0">DOMTokenList</a></code> interface must stringify to
   the object's underlying string representation.

  <h4 id=dom-feature><span class=secno>2.3.3. </span>DOM feature strings</h4>

  <p>DOM3 Core defines mechanisms for checking for interface support, and for
   obtaining implementations of interfaces, using <a
   href="http://www.w3.org/TR/DOM-Level-3-Core/core.html#DOMFeatures">feature
   strings</a>. <a href="#refsDOM3CORE">[DOM3CORE]</a>

  <p>A DOM application can use the <dfn id=hasfeature
   title=hasFeature><code>hasFeature(<var title="">feature</var>, <var
   title="">version</var>)</code></dfn> method of the
   <code>DOMImplementation</code> interface with parameter values "<code
   title="">HTML</code>" and "<code>5.0</code>" (respectively) to determine
   whether or not this module is supported by the implementation. In addition
   to the feature string "<code title="">HTML</code>", the feature string
   "<code title="">XHTML</code>" (with version string "<code>5.0</code>") can
   be used to check if the implementation supports XHTML. User agents should
   respond with a true value when the <code><a
   href="#hasfeature">hasFeature</a></code> method is queried with these
   values. Authors are cautioned, however, that UAs returning true might not
   be perfectly compliant, and that UAs returning false might well have
   support for features in this specification; in general, therefore, use of
   this method is discouraged.

  <p>The values "<code title="">HTML</code>" and "<code
   title="">XHTML</code>" (both with version "<code>5.0</code>") should also
   be supported in the context of the <code>getFeature()</code> and
   <code>isSupported()</code> methods, as defined by DOM3 Core.

  <p class=note>The interfaces defined in this specification are not always
   supersets of the interfaces defined in DOM2 HTML; some features that were
   formerly deprecated, poorly supported, rarely used or considered
   unnecessary have been removed. Therefore it is not guarenteed that an
   implementation that supports "<code title="">HTML</code>"
   "<code>5.0</code>" also supports "<code title="">HTML</code>"
   "<code>2.0</code>".

  <h3 id=dom-tree><span class=secno>2.4. </span><dfn id=dom-tree0>DOM tree
   accessors</dfn></h3>

  <p><dfn id=the-html0>The <code>html</code> element</dfn> of a document is
   the document's root element, if there is one and it's an <code><a
   href="#html">html</a></code> element, or null otherwise.

  <p><dfn id=the-head0>The <code>head</code> element</dfn> of a document is
   the first <code><a href="#head">head</a></code> element that is a child of
   <a href="#the-html0">the <code>html</code> element</a>, if there is one,
   or null otherwise.

  <p><dfn id=the-title1>The <code>title</code> element</dfn> of a document is
   the first <code><a href="#title1">title</a></code> element that is a child
   of <a href="#the-head0">the <code>head</code> element</a>, if there is
   one, or null otherwise.

  <p>The <dfn id=document.title
   title=dom-document-title><code>title</code></dfn> attribute must, on
   getting, run the following algorithm:

  <ol>
   <li>
    <p>If the <a href="#root-element">root element</a> is an <code>svg</code>
     element in the "<code title="">http://www.w3.org/2000/svg</code>"
     namespace, and the user agent supports SVG, then the getter must return
     the value that would have been returned by the DOM attribute of the same
     name on the <code>SVGDocument</code> interface.

   <li>
    <p>Otherwise, it must return a concatenation of the data of all the child
     <a href="#text-node" title="text node">text nodes</a> of <a
     href="#the-title1">the <code>title</code> element</a>, in tree order, or
     the empty string if <a href="#the-title1">the <code>title</code>
     element</a> is null.
  </ol>

  <p>On setting, the following algorithm must be run:

  <ol>
   <li>
    <p>If the <a href="#root-element">root element</a> is an <code>svg</code>
     element in the "<code title="">http://www.w3.org/2000/svg</code>"
     namespace, and the user agent supports SVG, then the setter must defer
     to the setter for the DOM attribute of the same name on the
     <code>SVGDocument</code> interface. Stop the algorithm here.

   <li>If <a href="#the-head0">the <code>head</code> element</a> is null,
    then the attribute must do nothing. Stop the algorithm here.

   <li>If <a href="#the-title1">the <code>title</code> element</a> is null,
    then a new <code><a href="#title1">title</a></code> element must be
    created and appended to <a href="#the-head0">the <code>head</code>
    element</a>.

   <li>The children of <a href="#the-title1">the <code>title</code>
    element</a> (if any) must all be removed.

   <li>A single <code>Text</code> node whose data is the new value being
    assigned must be appended to <a href="#the-title1">the <code>title</code>
    element</a>.
  </ol>

  <p>The <code title=dom-document-title><a
   href="#document.title">title</a></code> attribute on the <code><a
   href="#htmldocument">HTMLDocument</a></code> interface should shadow the
   attribute of the same name on the <code>SVGDocument</code> interface when
   the user agent supports both HTML and SVG.

  <p><dfn id=the-body0>The body element</dfn> of a document is the first
   child of <a href="#the-html0">the <code>html</code> element</a> that is
   either a <code><a href="#body0">body</a></code> element or a
   <code>frameset</code> element. If there is no such element, it is null. If
   the body element is null, then when the specification requires that events
   be fired at "the body element", they must instead be fired at the
   <code>Document</code> object.

  <p>The <dfn id=body title=dom-document-body><code>body</code></dfn>
   attribute, on getting, must return <a href="#the-body0">the body
   element</a> of the document (either a <code><a
   href="#body0">body</a></code> element, a <code>frameset</code> element, or
   null). On setting, the following algorithm must be followed:

  <ol>
   <li>If the new value is not a <code><a href="#body0">body</a></code> or
    <code>frameset</code> element, then raise a
    <code>HIERARCHY_REQUEST_ERR</code> exception and abort these steps.

   <li>Otherwise, if the new value is the same as <a href="#the-body0">the
    body element</a>, do nothing. Abort these steps.

   <li>Otherwise, if <a href="#the-body0">the body element</a> is not null,
    then replace that element with the new value in the DOM, as if the root
    element's <code title="">replaceChild()</code> method had been called
    with the new value and <a href="#the-body0" title="the body element">the
    incumbent body element</a> as its two arguments respectively, then abort
    these steps.

   <li>Otherwise, the <a href="#the-body0">the body element</a> is null.
    Append the new value to the root element.
  </ol>
  <!--XXX
    http://lxr.mozilla.org/seamonkey/source/content/html/document/src/nsHTMLDocument.cpp
    search for ::GetBody ::SetBody
    http://trac.webkit.org/projects/webkit/browser/trunk/WebCore/html/HTMLDocument.cpp
    search for ::setBody
    http://trac.webkit.org/projects/webkit/browser/trunk/WebCore/dom/Document.cpp
    search for ::body
  -->

  <p>The <dfn id=images0 title=dom-document-images><code>images</code></dfn>
   attribute must return an <code><a
   href="#htmlcollection0">HTMLCollection</a></code> rooted at the
   <code>Document</code> node, whose filter matches only <code><a
   href="#img">img</a></code> elements.

  <p>The <dfn id=links0 title=dom-document-links><code>links</code></dfn>
   attribute must return an <code><a
   href="#htmlcollection0">HTMLCollection</a></code> rooted at the
   <code>Document</code> node, whose filter matches only <code><a
   href="#a">a</a></code> elements with <code title=attr-hyperlink-href><a
   href="#href6">href</a></code> attributes and <code><a
   href="#area">area</a></code> elements with <code
   title=attr-hyperlink-href><a href="#href6">href</a></code> attributes.

  <p>The <dfn id=forms0 title=dom-document-forms><code>forms</code></dfn>
   attribute must return an <code><a
   href="#htmlcollection0">HTMLCollection</a></code> rooted at the
   <code>Document</code> node, whose filter matches only <code>form</code>
   elements.

  <p>The <dfn id=anchors
   title=dom-document-anchors><code>anchors</code></dfn> attribute must
   return an <code><a href="#htmlcollection0">HTMLCollection</a></code>
   rooted at the <code>Document</code> node, whose filter matches only
   <code><a href="#a">a</a></code> elements with <code
   title=attr-a-name>name</code> attributes.</p>
  <!-- XXX note that such elements are
  non-conforming -->

  <p>The <dfn id=getelementsbyname
   title=dom-document-getElementsByName><code>getElementsByName(<var
   title="">name</var>)</code></dfn> method a string <var
   title="">name</var>, and must return a live <code>NodeList</code>
   containing all the <code><a href="#a">a</a></code>, <code>applet</code>,
   <code>button</code>, <code>form</code>, <!-- frame? frameset?
  XXX--><code><a
   href="#iframe">iframe</a></code>, <code><a href="#img">img</a></code>,
   <code>input</code>, <code><a href="#map">map</a></code>, <code><a
   href="#meta0">meta</a></code>, <code><a
   href="#object">object</a></code>,<!-- param?
  XXX--> <code>select</code>,
   and <code>textarea</code> elements in that document that have a <code
   title="">name</code> attribute whose value is
   equal<!-- XXX case sensitivity --> to the <var title="">name</var>
   argument.</p>
  <!-- XXX what about XHTML? -->

  <p>The <dfn id=getelementsbyclassname
   title=dom-document-getElementsByClassName><code>getElementsByClassName(<var
   title="">classNames</var>)</code></dfn> method takes an array of strings
   representing classes. When called, the method must return a live
   <code>NodeList</code> object containing all the elements in the document
   that have all the classes specified in that array. If the array is empty,
   then the method must return an empty <code>NodeList</code>.

  <p>HTML, XHTML, SVG and MathML elements define which classes they are in by
   having an attribute in the per-element partition with the name <code
   title="">class</code> containing a space-separated list of classes to
   which the element belongs. Other specifications may also allow elements in
   their namespaces to be labelled as being in specific classes. UAs must not
   assume that all attributes of the name <code>class</code> for elements in
   any namespace work in this way, however, and must not assume that such
   attributes, when used as global attributes, label other elements as being
   in specific classes.

  <div class=example>
   <p>Given the following XHTML fragment:</p>

   <pre>&lt;div id="example"&gt;
 &lt;p id="p1" class="aaa bbb"/&gt;
 &lt;p id="p2" class="aaa ccc"/&gt;
 &lt;p id="p3" class="bbb ccc"/&gt;
&lt;/div&gt;</pre>

   <p>A call to
    <code>document.getElementById('example').getElementsByClassName('aaa')</code>
    would return a <code>NodeList</code> with the two paragraphs
    <code>p1</code> and <code>p2</code> in it.</p>

   <p>A call to <code>getElementsByClassName(['ccc', 'bbb'])</code> would
    only return one node, however, namely <code>p3</code>. A call to
    <code>document.getElementById('example').getElementsByClassName('ccc
    bbb')</code> would return the same thing.</p>

   <p>A call to <code>getElementsByClassName(['aaa bbb'])</code> would return
    no nodes; none of the elements above are in the "aaa bbb" class.</p>

   <p>A call to <code>getElementsByClassName([''])</code> would also return
    no nodes, since none of the nodes are in the "" class (indeed, in HTML,
    it is impossible to specify that an element is in the "" class).</p>
  </div>

  <p>The <dfn id=getelementsbyclassname0
   title=dom-getElementsByClassName><code>getElementsByClassName()</code></dfn>
   method on the <code><a href="#htmlelement">HTMLElement</a></code>
   interface must return the nodes that the <code><a
   href="#htmldocument">HTMLDocument</a></code> <code
   title=dom-document-getElementsByClassName><a
   href="#getelementsbyclassname">getElementsByClassName()</a></code> method
   would return, excluding any elements that are not descendants of the
   <code><a href="#htmlelement">HTMLElement</a></code> object on which the
   method was invoked.</p>
  <!-- XXX
>         * xGetParentElementByClassName(rootElement, className, tagName) -
> Navigates upwards until we hit a parent element with the given class name and
> optional tag name.
-->

  <p class=note>The <code title=dom-document-dir><a
   href="#dir1">dir</a></code> attribute on the <code><a
   href="#htmldocument">HTMLDocument</a></code> interface is defined along
   with the <code title=attr-dir><a href="#dir">dir</a></code> content
   attribute.

  <h3 id=dynamic><span class=secno>2.5. </span><dfn id=dynamic2>Dynamic
   markup insertion</dfn></h3>

  <p>The <code title=dom-document-write><a
   href="#document.write">document.write()</a></code> family of methods and
   the <code title=dom-innerHTML><a href="#innerhtml">innerHTML</a></code>
   family of DOM attributes enable script authors to dynamically insert
   markup into the document.

  <p class=issue>bz argues that innerHTML should be called something else on
   XML documents and XML elements. Is the sanity worth the migration pain?

  <p>Because these APIs interact with the parser, their behaviour varies
   depending on whether they are used with <a href="#html-">HTML
   documents</a> (and the <a href="#html-0">HTML parser</a>) or XHTML in <a
   href="#xml-documents">XML documents</a> (and the <span>XML parser</span>).
   The following table cross-references the various versions of these APIs.

  <table>
   <thead>
    <tr>
     <td>

     <th><dfn id=document.write
      title=dom-document-write><code>document.write()</code></dfn>

     <th><dfn id=innerhtml title=dom-innerHTML><code>innerHTML</code></dfn>

   <tbody>
    <tr>
     <th>For documents that are <a href="#html-">HTML documents</a>

     <td><a href="#document.write0"
      title=dom-document-write-HTML><code>document.write()</code> in HTML</a>

     <td><a href="#innerhtml0"
      title=dom-innerHTML-HTML><code>innerHTML</code> in HTML</a>

    <tr>
     <th>For documents that are <a href="#xml-documents">XML documents</a>

     <td><a href="#document.write1"
      title=dom-document-write-XML><code>document.write()</code> in XML</a>

     <td><a href="#innerhtml2" title=dom-innerHTML-XML><code>innerHTML</code>
      in XML</a>
  </table>

  <p>Regardless of the parsing mode, the <dfn id=document.writeln
   title=dom-document-writeln><code>document.writeln(<var
   title="">s</var>)</code></dfn> method must call the <code
   title=dom-document-write><a
   href="#document.write">document.write()</a></code> method with the same
   argument <var title="">s</var>, and then call the <code
   title=dom-document-write><a
   href="#document.write">document.write()</a></code> method with, as its
   argument, a string consisting of a single line feed character (U+000A).

  <h4 id=controlling><span class=secno>2.5.1. </span>Controlling the input
   stream</h4>

  <p>The <dfn id=open title=dom-document-open><code>open()</code></dfn>
   method comes in several variants with different numbers of arguments.

  <p>When called with two or fewer arguments, the method must act as follows:

  <ol>
   <li>
    <p>Let <var title="">type</var> be the value of the first argument, if
     there is one, or "<code>text/html</code>" otherwise.

   <li>
    <p>Let <var title="">replace</var> be true if there is a second argument
     and it has the value "replace"<!-- case-insensitive. XXX
   -->, and
     false otherwise.

   <li>
    <p>If the document has an <span>active parser</span><!-- XXX xref
    -->
     that isn't a <a href="#script-created">script-created parser</a>, and
     the <a href="#insertion">insertion point</a> associated with that
     parser's <a href="#input0">input stream</a> is not undefined (that is,
     it <em>does</em> point to somewhere in the input stream), then the
     method does nothing. Abort these steps.</p>

    <p class=note>This basically causes <code title=dom-document-open><a
     href="#open">document.open()</a></code> to be ignored when it's called
     in an inline script found during the parsing of data sent over the
     network, while still letting it have an effect when called
     asynchronously or on a document that is itself being spoon-fed using
     these APIs.</p>

   <li>
    <p class=big-issue>onbeforeunload, onunload

   <li>
    <p>If the document has an <span>active parser</span><!--XXX
   xref-->,
     then stop that parser, and throw away any pending content in the input
     stream. <span class=big-issue>what about if it doesn't, because it's
     either like a text/plain, or Atom, or PDF, or XHTML, or image document,
     or something?</span>
   </li>
   <!-- XXX see
   also innerHTML in HTML -->

   <li>
    <p>Remove all child nodes of the document.

   <li>
    <p>Create a new <a href="#html-0">HTML parser</a> and associate it with
     the document. This is a <dfn id=script-created>script-created
     parser</dfn> (meaning that it can be closed by the <code
     title=dom-document-open><a href="#open">document.open()</a></code> and
     <code title=dom-document-close><a
     href="#close">document.close()</a></code> methods, and that the
     tokeniser will wait for an explicit call to <code
     title=dom-document-close><a href="#close">document.close()</a></code>
     before emitting an end-of-file token).

   <li>Mark the document as being an <a href="#html-" title="HTML
    documents">HTML document</a> (it might already be so-marked).</li>
   <!-- text/plain handling -->

   <li>
    <p>If <var title="">type</var> does not have the value
     "<code>text/html</code>"<!-- XXX matched how?
   -->, then act as if the
     tokeniser had emitted a <code><a href="#pre">pre</a></code> element
     start tag, then set the <a href="#html-0">HTML parser</a>'s <a
     href="#tokenisation0">tokenisation</a> stage's <a
     href="#content2">content model flag</a> to <em>PLAINTEXT</em>.

   <li>
    <p>If <var title="">replace</var> is false, then:

    <ol>
     <li>Remove all the entries in the <a href="#browsing0">browsing
      context</a>'s <a href="#session">session history</a> after the <a
      href="#current0">current entry</a> in its <code>Document</code>'s
      <code><a href="#history1">History</a></code> object

     <li>Remove any earlier entries that share the same <code>Document</code>

     <li>Add a new entry just before the last entry that is associated with
      the text that was parsed by the previous parser associated with the
      <code>Document</code> object, as well as the state of the document at
      the start of these steps. (This allows the user to step backwards in
      the session history to see the page before it was blown away by the
      <code title=dom-document-open><a
      href="#open">document.open()</a></code> call.)
    </ol>

   <li>
    <p>Finally, set the <a href="#insertion">insertion point</a> to point at
     just before the end of the <a href="#input0">input stream</a> (which at
     this point will be empty).
  </ol>

  <p class=big-issue>We shouldn't hard-code <code>text/plain</code> there. We
   should do it some other way, e.g. hand off to the section on
   content-sniffing and handling of incoming data streams, the part that
   defines how this all works when stuff comes over the network.</p>
  <!-- XXX Should we support XML/XHTML as a type to that method? -->

  <p>When called with three or more arguments, the <code
   title=dom-document-open><a href="#open">open()</a></code> method on the
   <code><a href="#htmldocument">HTMLDocument</a></code> object must call the
   <code title=dom-open><a href="#open2">open()</a></code> method on the
   <code><a href="#window">Window</a></code> interface of the object returned
   by the <code title=dom-document-defaultView>defaultView</code> attribute
   of the <code>DocumentView</code> interface of the <code><a
   href="#htmldocument">HTMLDocument</a></code> object, with the same
   arguments as the original call to the <code title=dom-document-open><a
   href="#open">open()</a></code> method. If the <code
   title=dom-document-defaultView>defaultView</code> attribute of the
   <code>DocumentView</code> interface of the <code><a
   href="#htmldocument">HTMLDocument</a></code> object is null, then the
   method must raise an <code>INVALID_ACCESS_ERR</code> exception.

  <p>The <dfn id=close title=dom-document-close><code>close()</code></dfn>
   method must do nothing if there is no <a
   href="#script-created">script-created parser</a> associated with the
   document. If there is such a parser, then, when the method is called, the
   user agent must insert an <a href="#explicit">explicit "EOF" character</a>
   at the <a href="#insertion">insertion point</a> of the parser's <a
   href="#input0">input stream</a>.

  <h4 id=dynamic0><span class=secno>2.5.2. </span>Dynamic markup insertion in
   HTML</h4>

  <p>In HTML, the <dfn id=document.write0
   title=dom-document-write-HTML><code>document.write(<var
   title="">s</var>)</code></dfn> method must act as follows:

  <ol>
   <li>
    <p>If the <a href="#insertion">insertion point</a> is undefined, the
     <code title=dom-document-open><a href="#open">open()</a></code> method
     must be called (with no arguments) on the <code
     title=Document>document</code> object. The <a
     href="#insertion">insertion point</a> will point at just before the end
     of the (empty) <a href="#input0">input stream</a>.</p>

   <li>
    <p>The string <var title="">s</var> must be inserted into the <a
     href="#input0">input stream</a><!-- XXX xref --> just before the <a
     href="#insertion">insertion point</a>.</p>

   <li>
    <p>If there is <a href="#the-script" title="the script that will execute
     as soon as the parser resumes">a script that will execute as soon as the
     parser resumes</a>, then the method must now return without further
     processing of the <a href="#input0">input stream</a>.</p>

   <li>
    <p>Otherwise, the tokeniser must process the characters that were
     inserted, one at a time, processing resulting tokens as they are
     emitted, and stopping when the tokeniser reaches the insertion point or
     when the processing of the tokeniser is aborted by the tree construction
     stage (this can happen if a <code><a href="#script0">script</a></code>
     start tag token is emitted by the tokeniser).

    <p class=note>If the <code title=dom-document-write-HTML><a
     href="#document.write0">document.write()</a></code> method was called
     from script executing inline (i.e. executing because the parser parsed a
     set of <code><a href="#script0">script</a></code> tags), then this is a
     <a href="#nestedParsing">reentrant invocation of the parser</a>.</p>

   <li>
    <p>Finally, the method must return.</p>
  </ol>

  <p>In HTML, the <dfn id=innerhtml0
   title=dom-innerHTML-HTML><code>innerHTML</code></dfn> DOM attribute of all
   <code><a href="#htmlelement">HTMLElement</a></code> and <code><a
   href="#htmldocument">HTMLDocument</a></code> nodes returns a serialisation
   of the node's children using the <span>HTML syntax</span><!-- XXX xref
  -->.
   On setting, it replaces the node's children with new nodes that result
   from parsing the given value. The formal definitions follow.

  <p>On getting, the <code title=dom-innerHTML-HTML><a
   href="#innerhtml0">innerHTML</a></code> DOM attribute must return the
   result of running the following algorithm:

  <ol>
   <li>
    <p>Let <var title="">s</var> be a string, and initialise it to the empty
     string.

   <li>
    <p>For each child node <var title="">child</var>, in <a
     href="#tree-order">tree order</a>, append the appropriate string from
     the following list to <var title="">s</var>:</p>

    <dl class=switch>
     <dt>If the child node is an <code title="">Element</code>

     <dd>
      <p>Append a U+003C LESS-THAN SIGN (<code title="">&lt;</code>)
       character, followed by the element's tag name. (For nodes created by
       the <a href="#html-0">HTML parser</a>, <code
       title="">Document.createElement()</code>, or <code
       title="">Document.renameNode()</code>, the tag name will be
       lowercase.)</p>

      <p>For each attribute that the element has, append a U+0020 SPACE
       character, the attribute's name (which, for attributes set by the <a
       href="#html-0">HTML parser</a> or by <code
       title="">Element.setAttributeNode()</code> or <code
       title="">Element.setAttribute()</code>, will be lowercase), a U+003D
       EQUALS SIGN (<code title="">=</code>) character, a U+0022 QUOTATION
       MARK (<code title="">&quot;</code>) character, the attribute's value,
       <a href="#escapingString" title="escaping a string">escaped as
       described below</a>, and a second U+0022 QUOTATION MARK (<code
       title="">&quot;</code>) character.</p>

      <p>While the exact order of attributes is UA-defined, and may depend on
       factors such as the order that the attributes were given in the
       original markup, the sort order must be stable, such that consecutive
       calls to <code title=dom-innerHTML-HTML><a
       href="#innerhtml0">innerHTML</a></code> serialise an element's
       attributes in the same order.</p>

      <p>Append a U+003E GREATER-THAN SIGN (<code title="">&gt;</code>)
       character.</p>

      <p>If the child node is an <code><a href="#area">area</a></code>,
       <code><a href="#base">base</a></code>, <code>basefont</code>,
       <code>bgsound</code>, <code><a href="#br">br</a></code>, <code><a
       href="#col">col</a></code>, <code><a href="#embed">embed</a></code>,
       <code>frame</code>, <code><a href="#hr">hr</a></code>, <code><a
       href="#img">img</a></code>, <code>input</code>, <code><a
       href="#link">link</a></code>, <code><a href="#meta0">meta</a></code>,
       <code><a href="#param">param</a></code>, <code>spacer</code>, or
       <code>wbr</code> element, then continue on to the next child node at
       this point.</p>
      <!-- also, i guess:
      image, isindex, and keygen, but we don't list those because we
      don't consider those "elements", more "macros", and thus we
      should never serialise them -->
      <!-- XXX when we get around to
      it, add event-source -->
      <p>Otherwise, append the value of the <var title="">child</var>
       element's <code title=dom-innerHTML-HTML><a
       href="#innerhtml0">innerHTML</a></code> DOM attribute (thus recursing
       into this algorithm for that element), followed by a U+003C LESS-THAN
       SIGN (<code title="">&lt;</code>) character, a U+002F SOLIDUS (<code
       title="">/</code>) character, the element's tag name again, and
       finally a U+003E GREATER-THAN SIGN (<code title="">&gt;</code>)
       character.</p>

     <dt>If the child node is a <code title="">Text</code> or <code
      title="">CDATASection</code> node

     <dd>
      <p>If one of the ancestors of the child node is a <code><a
       href="#style">style</a></code>, <code><a
       href="#script0">script</a></code>, <code>xmp</code>, <code><a
       href="#iframe">iframe</a></code>, <code>noembed</code>,
       <code>noframes</code>, or <code><a
       href="#noscript">noscript</a></code> element, then append the value of
       the <var title="">child</var> node's <code title="">data</code> DOM
       attribute literally.</p>
      <!-- note about noscript: because this is defining an API, it
      can assume that scripting is enabled, and that thus the
      <noscript> element in the DOM will have been parsed in the
      scripting-enabled mode, and that thus the text node is raw
      markup -->
      
      <p>Otherwise, append the value of the <var title="">child</var> node's
       <code title="">data</code> DOM attribute, <a href="#escapingString"
       title="escaping a string">escaped as described below</a>.</p>

     <dt>If the child node is a <code title="">Comment</code>

     <dd>
      <p>Append the literal string <code>&lt;!--</code> (U+003C LESS-THAN
       SIGN, U+0021 EXCLAMATION MARK, U+002D HYPHEN-MINUS, U+002D
       HYPHEN-MINUS), followed by the value of the <var title="">child</var>
       node's <code title="">data</code> DOM attribute, followed by the
       literal string <code>--&gt;</code> (U+002D HYPHEN-MINUS, U+002D
       HYPHEN-MINUS, U+003E GREATER-THAN SIGN).</p>

     <dt>If the child node is a <code title="">DocumentType</code>

     <dd>
      <p>Append the literal string <code>&lt;!DOCTYPE</code> (U+003C
       LESS-THAN SIGN, U+0021 EXCLAMATION MARK, U+0044 LATIN CAPITAL LETTER
       D, U+004F LATIN CAPITAL LETTER O, U+0043 LATIN CAPITAL LETTER C,
       U+0054 LATIN CAPITAL LETTER T, U+0059 LATIN CAPITAL LETTER Y, U+0050
       LATIN CAPITAL LETTER P, U+0045 LATIN CAPITAL LETTER E), followed by a
       space (U+0020 SPACE), followed by the value of the <var
       title="">child</var> node's <code title="">name</code> DOM attribute,
       followed by the literal string <code>&gt;</code> (U+003E GREATER-THAN
       SIGN).</p>
    </dl>

    <p>Other nodes types (e.g. <code title="">Attr</code>) cannot occur as
     children of elements. If they do, the <code title=dom-innerHTML-HTML><a
     href="#innerhtml0">innerHTML</a></code> attribute must raise an
     <code>INVALID_STATE_ERR</code> exception.</p>

   <li>
    <p>The result of the algorithm is the string <var title="">s</var>.
  </ol>

  <p><dfn id=escapingString>Escaping a string</dfn> (for the purposes of the
   algorithm above) consists of replacing any occurances of the "<code
   title="">&amp;</code>" character by the string "<code
   title="">&amp;amp;</code>", any occurances of the "<code
   title="">&lt;</code>" character by the string "<code
   title="">&amp;lt;</code>", any occurances of the "<code
   title="">&gt;</code>" character by the string "<code
   title="">&amp;gt;</code>", and any occurances of the "<code
   title="">&quot;</code>" character by the string "<code
   title="">&amp;quot;</code>".

  <p class=note>Entity reference nodes are <a
   href="#entity-references">assumed to be expanded</a> by the user agent,
   and are therefore not covered in the algorithm above.

  <p class=note>If the element's contents are not conformant, it is possible
   that the roundtripping through <code title=dom-innerHTML-HTML><a
   href="#innerhtml0">innerHTML</a></code> will not work. For instance, if
   the element is a <code>textarea</code> element to which a <code
   title="">Comment</code> node has been appended, then assigning <code
   title=dom-innerHTML-HTML><a href="#innerhtml0">innerHTML</a></code> to
   itself will result in the comment being displayed in the text field.
   Similarly, if, as a result of DOM manipulation, the element contains a
   comment that contains the literal string "<code title="">--&gt;</code>",
   then when the result of serialising the element is parsed, the comment
   will be truncated at that point and the rest of the comment will be
   interpreted as markup. Another example would be making a <code><a
   href="#script0">script</a></code> element contain a text node with the
   text string "<code>&lt;/script></code>".

  <p>On setting, if the node is a document, the <code
   title=dom-innerHTML-HTML><a href="#innerhtml0">innerHTML</a></code> DOM
   attribute must run the following algorithm:

  <ol>
   <li>
    <p>Otherwise, if the document has an <span>active
     parser</span><!--XXX xref-->, then stop that parser, and throw away any
     pending content in the input stream. <span class=big-issue>what about if
     it doesn't, because it's either like a text/plain, or Atom, or PDF, or
     XHTML, or image document, or something?</span></p>
    <!-- XXX see also document.open() -->

   <li>
    <p>The user agent must remove the children nodes of the
     <code>Document</code> whose <code title=dom-innerHTML-HTML><a
     href="#innerhtml0">innerHTML</a></code> attribute is being set.</p>

   <li>
    <p>The user agent must create a new <a href="#html-0">HTML parser</a>, in
     its initial state, and associate it with the <code>Document</code> node.</p>
   </li>
   <!-- redundant, the document is forcably already so labelled if we get here
   <li>

    <p>The user agent must mark the <code>Document</code> object as
    being an <span title="HTML documents">HTML document</span>.</p>

   </li>
-->

   <li>
    <p>The user agent must place into the <a href="#input0">input stream</a>
     for the <a href="#html-0">HTML parser</a> just created the string being
     assigned into the <code title=dom-innerHTML-HTML><a
     href="#innerhtml0">innerHTML</a></code> attribute.</p>

   <li>
    <p>The user agent must start the parser and let it run until it has
     consumed all the characters just inserted into the input stream. (The
     <code>Document</code> node will have been populated with elements and a
     <code title=event-load><a href="#load0">load</a></code> event will have
     fired on <a href="#the-body0" title="the body element">its body
     element</a>.)</p>
  </ol>

  <p>Otherwise, if the node is an element, then setting the <code
   title=dom-innerHTML-HTML><a href="#innerhtml0">innerHTML</a></code> DOM
   attribute must cause the following algorithm to run instead:

  <ol>
   <li>
    <p>The user agent must create a new <code>Document</code> node, and mark
     it as being an <a href="#html-" title="HTML documents">HTML
     document</a>.</p>

    <p>The user agent must create a new <a href="#html-0">HTML parser</a>,
     and associate it with the just created <code>Document</code> node.</p>

    <p class=note>Parts marked <dfn id=innerhtml1 title="innerHTML
     case"><code>innerHTML</code> case</dfn> in algorithms in the parser
     section are parts that only occur if the parser was created for the
     purposes of handling the setting of an element's <code
     title=dom-innerHTML-HTML><a href="#innerhtml0">innerHTML</a></code>
     attribute. The algorithms have been annotated with such markings for
     informational purposes only; such markings have no normative weight. If
     it is possible for a condition described as an <a
     href="#innerhtml1"><code>innerHTML</code> case</a> to occur even when
     the parser wasn't created for the purposes of handling an element's
     <code title=dom-innerHTML-HTML><a
     href="#innerhtml0">innerHTML</a></code> attribute, then that is an error
     in the specification.</p>

   <li>
    <p>The user agent must set the <a href="#html-0">HTML parser</a>'s <a
     href="#tokenisation0">tokenisation</a> stage's <a
     href="#content2">content model flag</a> according to the name of the
     element whose <code title=dom-innerHTML-HTML><a
     href="#innerhtml0">innerHTML</a></code> attribute is being set, as
     follows:</p>

    <dl class=switch>
     <dt>If it is a <code><a href="#title1">title</a></code> or
      <code>textarea</code> element

     <dd>Set the <a href="#content2">content model flag</a> to
      <em>RCDATA</em>.

     <dt>If it is a <code><a href="#style">style</a></code>, <code><a
      href="#script0">script</a></code>, <code>xmp</code>, <code><a
      href="#iframe">iframe</a></code>, <code>noembed</code>,
      <code>noframes</code>, or <code><a href="#noscript">noscript</a></code>
      element

     <dd>Set the <a href="#content2">content model flag</a> to
      <em>CDATA</em>.</dd>
     <!-- note about noscript: we set it to CDATA here because if
     someone is setting innerHTML, then we know scripting is enabled,
     so the noscript element will be in CDATA mode -->

     <dt>If it is a <code>plaintext</code> element

     <dd>Set the <a href="#content2">content model flag</a> to
      <em>PLAINTEXT</em>.

     <dt>Otherwise

     <dd>Set the <a href="#content2">content model flag</a> to
      <em>PCDATA</em>.
    </dl>

   <li>
    <p>The user agent must switch the <a href="#html-0">HTML parser</a>'s <a
     href="#tree-construction0">tree construction</a> stage to <a
     href="#the-main0">the main phase</a>.

   <li>
    <p>Let <var title="">root</var> be a new <code><a
     href="#html">html</a></code> element with no attributes.</p>

   <li>
    <p>The user agent must append the element <var title="">root</var> to the
     <code>Document</code> node created above.</p>

   <li>
    <p>The user agent must set up the parser's <a href="#stack">stack of open
     elements</a> so that it contains just the single element <var
     title="">root</var>.</p>

   <li>
    <p>The user agent must <a href="#reset" title="reset the insertion mode
     appropriately">reset the parser's insertion mode appropriately</a>.</p>

   <li>
    <p>The user agent must set the parser's <a
     href="#form-element"><code>form</code> element pointer</a> to the
     nearest node to the element whose <code title=dom-innerHTML-HTML><a
     href="#innerhtml0">innerHTML</a></code> attribute is being set that is a
     <code>form</code> element (going straight up the ancestor chain, and
     including the element itself, if it is a <code>form</code> element), or,
     if there is no such <code>form</code> element, to null.</p>

   <li>
    <p>The user agent must place into the <a href="#input0">input stream</a>
     for the <a href="#html-0">HTML parser</a> just created the string being
     assigned into the <code title=dom-innerHTML-HTML><a
     href="#innerhtml0">innerHTML</a></code> attribute.</p>

   <li>
    <p>The user agent must start the parser and let it run until it has
     consumed all the characters just inserted into the input stream.</p>

   <li>
    <p>The user agent must remove the children of the element whose <code
     title=dom-innerHTML-HTML><a href="#innerhtml0">innerHTML</a></code>
     attribute is being set.</p>

   <li>
    <p>The user agent must move all the child nodes of the <var
     title="">root</var> element to the element whose <code
     title=dom-innerHTML-HTML><a href="#innerhtml0">innerHTML</a></code>
     attribute is being set, preserving their order.</p>
  </ol>
  <!-- XXX must make sure we spec that innerHTML causes mutation
  events to fire, but document.write() doesn't. (the latter is already
  req-stated in the parser section, btw) -->
  <!-- http://msdn.microsoft.com/workshop/author/dhtml/reference/properties/innerhtml.asp -->
  <!-- http://lxr.mozilla.org/seamonkey/source/content/html/content/src/nsGenericHTMLElement.cpp#879
       note script execution disabled
       http://lxr.mozilla.org/seamonkey/source/content/base/src/nsContentUtils.cpp#3308
       http://trac.webkit.org/projects/webkit/browser/trunk/WebCore/html/HTMLElement.cpp#L295
       http://trac.webkit.org/projects/webkit/browser/trunk/WebCore/html/HTMLElement.cpp#L242
       http://trac.webkit.org/projects/webkit/browser/trunk/WebCore/html/HTMLTokenizer.cpp#L1742
   -->

  <h4 id=dynamic1><span class=secno>2.5.3. </span>Dynamic markup insertion in
   XML</h4>

  <p>In an XML context, the <dfn id=document.write1
   title=dom-document-write-XML><code>document.write(<var
   title="">s</var>)</code></dfn> method must raise an
   <code>INVALID_ACCESS_ERR</code> exception.</p>
  <!--
  For XHTML: content must be well-formed. Where does
  it insert? Immediately after the script that called document.write()?</p>
  how do we handle async scripts vs sync scripts?

Consider:
data:text/xml,<script xmlns="http://www.w3.org/1999/xhtml"><![CDATA[ document.write('<foo>Test</foo>'); ]]></script>
data:text/xml,<script xmlns="http://www.w3.org/1999/xhtml"><![CDATA[ alert('test'); alert(document.write); try { document.write('<foo>Test</foo>'); alert(document.childNodes.length); } catch (e) { alert(e); } ]]></script>

-->

  <p>The <dfn id=innerhtml2
   title=dom-innerHTML-XML><code>innerHTML</code></dfn> attributes, on the
   other hand, in an XML context, are usable.

  <p>On getting, the <code title=dom-innerHTML-XML><a
   href="#innerhtml2">innerHTML</a></code> DOM attribute on <code><a
   href="#htmlelement">HTMLElement</a></code>s and <code><a
   href="#htmldocument">HTMLDocument</a></code>s, in an XML context, must
   return an XML namespace-well-formed internal general parsed entity
   representation of the element or document. User agents may adjust prefixes
   and namespace declarations in the serialisation (and indeed might be
   forced to do so in some cases to obtain namespace-well-formed XML). <a
   href="#refsXML">[XML]</a> <a href="#refsXMLNS">[XMLNS]</a>

  <p>On setting, in an XML context, the <code title=dom-innerHTML-HTML><a
   href="#innerhtml0">innerHTML</a></code> DOM attribute on must run the
   following algorithm:

  <ol>
   <li>
    <p>The user agent must create a new <span>XML parser</span>.</p>

   <li>
    <p>If the <code title=dom-innerHTML-XML><a
     href="#innerhtml2">innerHTML</a></code> attribute is being set on an
     element, the user agent must <span>feed the parser</span> just created
     the string corresponding to the start tag of that element, declaring all
     the namespace prefixes that are in scope on that element in the DOM, as
     well as declaring the default namespace (if any) that is in scope on
     that element in the DOM.</p>

   <li>
    <p>The user agent must <span>feed the parser</span> just created the
     string being assigned into the <code title=dom-innerHTML-HTML><a
     href="#innerhtml0">innerHTML</a></code> attribute.</p>

   <li>
    <p>If the <code title=dom-innerHTML-XML><a
     href="#innerhtml2">innerHTML</a></code> attribute is being set on an
     element, the user agent must <span>feed the parser</span> the string
     corresponding to the end tag of that element.</p>

   <li>
    <p>If the parser found a well-formedness error, the attribute's setter
     must raise a <code>SYNTAX_ERR</code> exception and abort these steps.</p>

   <li>
    <p>The user agent must remove the children nodes of the node whose <code
     title=dom-innerHTML-XML><a href="#innerhtml2">innerHTML</a></code>
     attribute is being set.</p>

   <li>
    <p>If the attribute is being set on a <code>Document</code> node, let
     <var title="">new children</var> be the children of the document,
     preserving their order. Otherwise, the attribute is being set on an
     <code>Element</code> node; let <var title="">new children</var> be the
     children of the the document's root element, preserving their order.</p>

   <li>
    <p>If the attribute is being set on a <code>Document</code> node, let
     <var title="">target document</var> be that <code>Document</code> node.
     Otherwise, the attribute is being set on an <code>Element</code> node;
     let <var title="">target document</var> be the <code
     title="">ownerDocument</code> of that <code>Element</code>.</p>

   <li>
    <p>Set the <code title="">ownerDocument</code> of all the nodes in <var
     title="">new children</var> to the <var title="">target document</var>.</p>

   <li>
    <p>Append all the <var title="">new children</var> nodes to the node
     whose <code title=dom-innerHTML-HTML><a
     href="#innerhtml0">innerHTML</a></code> attribute is being set,
     preserving their order.</p>
  </ol>

  <h3 id=apis-in><span class=secno>2.6. </span>APIs in HTML documents</h3>
  <!-- XXX case-sensitivity training required here. -->

  <p>For <a href="#html-">HTML documents</a>, and for <a
   href="#html-elements">HTML elements</a> in <a href="#html-">HTML
   documents</a>, certain APIs defined in DOM3 Core become case-insensitive
   or case-changing, as sometimes defined in DOM3 Core, and as summarised or
   required below. <a href="#refsDOM3CORE">[DOM3CORE]</a>.

  <p>This does not apply to <a href="#xml-documents">XML documents</a> or to
   elements that are not in the <a href="#html-namespace0">HTML namespace</a>
   despite being in <a href="#html-">HTML documents</a>.

  <dl>
   <dt><code title="">Element.tagName</code>, <code
    title="">Node.nodeName</code>, and <code title="">Node.localName</code>

   <dd>
    <p>These attributes return tag names in all uppercase<!-- XXX
    xref-->
     and attribute names in all lowercase<!-- XXX xref -->, regardless of the
     case with which they were created.</p>

   <dt><code title="">Document.createElement()</code>

   <dd>
    <p>The canonical form of HTML markup is all-lowercase; thus, this method
     will lowercase<!-- XXX xref --> the argument before creating the
     requisite element. Also, the element created must be in the <a
     href="#html-namespace0">HTML namespace</a>.</p>

    <p class=note>This doesn't apply to <code
     title="">Document.createElementNS()</code>. Thus, it is possible, by
     passing this last method a tag name in the wrong case, to create an
     element that claims to have the tag name of an HTML element, but doesn't
     support its interfaces, because it really has another tag name not
     accessible from the DOM APIs.</p>

   <dt><code title="">Element.setAttributeNode()</code>

   <dd>
    <p>When an <code>Attr</code> node is set on an <a href="#html-elements"
     title="HTML elements">HTML element</a>, it must have its name
     lowercased<!-- XXX xref --> before the element is affected.</p>

    <p class=note>This doesn't apply to <code
     title="">Document.setAttributeNodeNS()</code>.</p>

   <dt><code title="">Element.setAttribute()</code>

   <dd>
    <p>When an attribute is set on an <a href="#html-elements" title="HTML
     elements">HTML element</a>, the name argument must be
     lowercased<!-- XXX xref
    --> before the element is affected.</p>

    <p class=note>This doesn't apply to <code
     title="">Document.setAttributeNS()</code>.</p>

   <dt><code title="">Document.getElementsByTagName()</code> and <code
    title="">Element.getElementsByTagName()</code>

   <dd>
    <p>These methods (but not their namespaced counterparts) must compare the
     given argument case-insensitively<!-- XXX xref --> when looking at <a
     href="#html-elements" title="HTML elements">HTML elements</a>, and
     case-sensitively otherwise.</p>

    <p class=note>Thus, in an <a href="#html-" title="HTML documents">HTML
     document</a> with nodes in multiple namespaces, these methods will be
     both case-sensitive and case-insensitive at the same time.</p>

   <dt><code title="">Document.renameNode()</code>

   <dd>
    <p>If the new namespace is the <a href="#html-namespace0">HTML
     namespace</a>, then the new qualified name must be lowercased before the
     rename takes place.<!-- XXX xref --></p>
  </dl>

  <h2 id=semantics><span class=secno>3. </span>Semantics and structure of
   HTML elements</h2>

  <h3 id=semantics-intro><span class=secno>3.1. </span>Introduction</h3>

  <p><em>This section is non-normative.</em>

  <p class=big-issue>An introduction to marking up a document.

  <h3 id=common1><span class=secno>3.2. </span>Common microsyntaxes</h3>

  <p>There are various places in HTML that accept particular data types, such
   as dates or numbers. This section describes what the conformance criteria
   for content in those formats is, and how to parse them.</p>
  <!-- XXX need to define how to handle U+000A LINE FEED and U+000D
  CARRIAGE RETURN in attributes (for HTML) -->

  <p class=big-issue>Need to go through the whole spec and make sure all the
   attribute values are clearly defined either in terms of microsyntaxes or
   in terms of other specs, or as "Text" or some such.

  <h4 id=common2><span class=secno>3.2.1. </span>Common parser idioms</h4>

  <p>The <dfn id=space title="space character">space characters</dfn>, for
   the purposes of this specification, are U+0020 SPACE, U+0009 CHARACTER
   TABULATION (tab), U+000A LINE FEED (LF), U+000B LINE TABULATION, U+000C
   FORM FEED (FF), and U+000D CARRIAGE RETURN (CR).

  <p>Some of the micro-parsers described below follow the pattern of having
   an <var title="">input</var> variable that holds the string being parsed,
   and having a <var title="">position</var> variable pointing at the next
   character to parse in <var title="">input</var>.

  <p>For parsers based on this pattern, a step that requires the user agent
   to <dfn id=collect>collect a sequence of characters</dfn> means that the
   following algorithm must be run, with <var title="">characters</var> being
   the set of characters that can be collected:

  <ol>
   <li>
    <p>Let <var title="">input</var> and <var title="">position</var> be the
     same variables as those of the same name in the algorithm that invoked
     these steps.

   <li>
    <p>Let <var title="">result</var> be the empty string.

   <li>
    <p>While <var title="">position</var> doesn't point past the end of <var
     title="">input</var> and the character at <var title="">position</var>
     is one of the <var title="">characters</var>, append that character to
     the end of <var title="">result</var> and advance <var
     title="">position</var> to the next character in <var
     title="">input</var>.

   <li>
    <p>Return <var title="">result</var>.
  </ol>

  <p>The step <dfn id=skip-whitespace>skip whitespace</dfn> means that the
   user agent must <a href="#collect">collect a sequence of characters</a>
   that are <a href="#space" title="space character">space characters</a>.
   The step <dfn id=skip->skip Zs characters</dfn> means that the user agent
   must <a href="#collect">collect a sequence of characters</a> that are in
   the Unicode character class Zs. In both cases, the collected characters
   are not used. <a href="#refsUNICODE">[UNICODE]</a>

  <h4 id=boolean><span class=secno>3.2.2. </span>Boolean attributes</h4>

  <p>A number of attributes in HTML5 are <dfn id=boolean0 title="boolean
   attribute">boolean attributes</dfn>. The presence of a boolean attribute
   on an element represents the true value, and the absence of the attribute
   represents the false value.

  <p>If the attribute is present, its value must either be the empty string
   or the attribute's canonical name, exactly, with no leading or trailing
   whitespace, and in lowercase.

  <h4 id=numbers><span class=secno>3.2.3. </span>Numbers</h4>

  <h5 id=unsigned><span class=secno>3.2.3.1. </span>Unsigned integers</h5>

  <p>A string is a <dfn id=valid>valid non-negative integer</dfn> if it
   consists of one of more characters in the range U+0030 DIGIT ZERO (0) to
   U+0039 DIGIT NINE (9).

  <p>The <dfn id=rules>rules for parsing non-negative integers</dfn> are as
   given in the following algorithm. When invoked, the steps must be followed
   in the order given, aborting at the first step that returns a value. This
   algorithm will either return zero, a positive integer, or an error.
   Leading spaces are ignored. Trailing spaces and indeed any trailing
   garbage characters are ignored.

  <ol>
   <li>
    <p>Let <var title="">input</var> be the string being parsed.

   <li>
    <p>Let <var title="">position</var> be a pointer into <var
     title="">input</var>, initially pointing at the start of the string.

   <li>
    <p>Let <var title="">value</var> have the value 0.

   <li>
    <p><a href="#skip-whitespace">Skip whitespace.</a>

   <li>
    <p>If <var title="">position</var> is past the end of <var
     title="">input</var>, return an error.

   <li>
    <p>If the next character is not one of U+0030 DIGIT ZERO (0) .. U+0039
     DIGIT NINE (9), then return an error.
   </li>
   <!-- Ok. At this point we know we have a number. It might have
   trailing garbage which we'll ignore, but it's a number, and we
   won't return an error. -->

   <li>
    <p>If the next character is one of U+0030 DIGIT ZERO (0) .. U+0039 DIGIT
     NINE (9):</p>

    <ol>
     <li>Multiply <var title="">value</var> by ten.

     <li>Add the value of the current character (0..9) to <var
      title="">value</var>.

     <li>Advance <var title="">position</var> to the next character.

     <li>If <var title="">position</var> is not past the end of <var
      title="">input</var>, return to the top of step 7 in the overall
      algorithm (that's the step within which these substeps find
      themselves).
    </ol>

   <li>
    <p>Return <var title="">value</var>.
  </ol>

  <h5 id=signed><span class=secno>3.2.3.2. </span>Signed integers</h5>

  <p>A string is a <dfn id=valid0>valid integer</dfn> if it consists of one
   of more characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE
   (9), optionally prefixed with a U+002D HYPHEN-MINUS ("-") character.

  <p>The <dfn id=rules0>rules for parsing integers</dfn> are similar to the
   rules for non-negative integers, and are as given in the following
   algorithm. When invoked, the steps must be followed in the order given,
   aborting at the first step that returns a value. This algorithm will
   either return an integer or an error. Leading spaces are ignored. Trailing
   spaces and trailing garbage characters are ignored.

  <ol>
   <li>
    <p>Let <var title="">input</var> be the string being parsed.

   <li>
    <p>Let <var title="">position</var> be a pointer into <var
     title="">input</var>, initially pointing at the start of the string.

   <li>
    <p>Let <var title="">value</var> have the value 0.

   <li>
    <p>Let <var title="">sign</var> have the value "positive".

   <li>
    <p><a href="#skip-whitespace">Skip whitespace.</a>

   <li>
    <p>If <var title="">position</var> is past the end of <var
     title="">input</var>, return an error.

   <li>
    <p>If the character indicated by <var title="">position</var> (the first
     character) is a U+002D HYPHEN-MINUS ("-") character:</p>

    <ol>
     <li>Let <var title="">sign</var> be "negative".

     <li>Advance <var title="">position</var> to the next character.

     <li>If <var title="">position</var> is past the end of <var
      title="">input</var>, return an error.
    </ol>

   <li>
    <p>If the next character is not one of U+0030 DIGIT ZERO (0) .. U+0039
     DIGIT NINE (9), then return an error.
   </li>
   <!-- Ok. At this point we know we have a number. It might have
   trailing garbage which we'll ignore, but it's a number, and we
   won't return an error. -->

   <li>
    <p>If the next character is one of U+0030 DIGIT ZERO (0) .. U+0039 DIGIT
     NINE (9):</p>

    <ol>
     <li>Multiply <var title="">value</var> by ten.

     <li>Add the value of the current character (0..9) to <var
      title="">value</var>.

     <li>Advance <var title="">position</var> to the next character.

     <li>If <var title="">position</var> is not past the end of <var
      title="">input</var>, return to the top of step 9 in the overall
      algorithm (that's the step within which these substeps find
      themselves).
    </ol>

   <li>
    <p>If <var title="">sign</var> is "positive", return <var
     title="">value</var>, otherwise return 0-<var title="">value</var>.
  </ol>

  <h5 id=real-numbers><span class=secno>3.2.3.3. </span>Real numbers</h5>

  <p>A string is a <dfn id=valid1>valid floating point number</dfn> if it
   consists of one of more characters in the range U+0030 DIGIT ZERO (0) to
   U+0039 DIGIT NINE (9), optionally with a single U+002E FULL STOP (".")
   character somewhere (either before these numbers, in between two numbers,
   or after the numbers), all optionally prefixed with a U+002D HYPHEN-MINUS
   ("-") character.

  <p>The <dfn id=rules1>rules for parsing floating point number values</dfn>
   are as given in the following algorithm. As with the previous algorithms,
   when this one is invoked, the steps must be followed in the order given,
   aborting at the first step that returns a value. This algorithm will
   either return a number or an error. Leading spaces are ignored. Trailing
   spaces and garbage characters are ignored.

  <ol>
   <li>
    <p>Let <var title="">input</var> be the string being parsed.

   <li>
    <p>Let <var title="">position</var> be a pointer into <var
     title="">input</var>, initially pointing at the start of the string.

   <li>
    <p>Let <var title="">value</var> have the value 0.

   <li>
    <p>Let <var title="">sign</var> have the value "positive".

   <li>
    <p><a href="#skip-whitespace">Skip whitespace.</a>

   <li>
    <p>If <var title="">position</var> is past the end of <var
     title="">input</var>, return an error.

   <li>
    <p>If the character indicated by <var title="">position</var> (the first
     character) is a U+002D HYPHEN-MINUS ("-") character:</p>

    <ol>
     <li>Let <var title="">sign</var> be "negative".

     <li>Advance <var title="">position</var> to the next character.

     <li>If <var title="">position</var> is past the end of <var
      title="">input</var>, return an error.
    </ol>

   <li>
    <p>If the next character is not one of U+0030 DIGIT ZERO (0) .. U+0039
     DIGIT NINE (9) or U+002E FULL STOP ("."), then return an error.

   <li>
    <p>If the next character is U+002E FULL STOP ("."), but either that is
     the last character or the character after that one is not one of U+0030
     DIGIT ZERO (0) .. U+0039 DIGIT NINE (9), then return an error.
   </li>
   <!-- Ok. At this point we know we have a number. It might have
   trailing garbage which we'll ignore, but it's a number, and we
   won't return an error. -->

   <li>
    <p>If the next character is one of U+0030 DIGIT ZERO (0) .. U+0039 DIGIT
     NINE (9):</p>

    <ol>
     <li>Multiply <var title="">value</var> by ten.

     <li>Add the value of the current character (0..9) to <var
      title="">value</var>.

     <li>Advance <var title="">position</var> to the next character.

     <li>If <var title="">position</var> is past the end of <var
      title="">input</var>, then if <var title="">sign</var> is "positive",
      return <var title="">value</var>, otherwise return 0-<var
      title="">value</var>.

     <li>Otherwise return to the top of step 10 in the overall algorithm
      (that's the step within which these substeps find themselves).
    </ol>

   <li>
    <p>Otherwise, if the next character is not a U+002E FULL STOP ("."), then
     if <var title="">sign</var> is "positive", return <var
     title="">value</var>, otherwise return 0-<var title="">value</var>.

   <li>
    <p>The next character is a U+002E FULL STOP ("."). Advance <var
     title="">position</var> to the character after that.

   <li>
    <p>Let <var title="">divisor</var> be 1.

   <li>
    <p>If the next character is one of U+0030 DIGIT ZERO (0) .. U+0039 DIGIT
     NINE (9):</p>

    <ol>
     <li>Multiply <var title="">divisor</var> by ten.

     <li>Add the value of the current character (0..9) divided by <var
      title="">divisor</var>, to <var title="">value</var>.

     <li>Advance <var title="">position</var> to the next character.

     <li>If <var title="">position</var> is past the end of <var
      title="">input</var>, then if <var title="">sign</var> is "positive",
      return <var title="">value</var>, otherwise return 0-<var
      title="">value</var>.

     <li>Otherwise return to the top of step 14 in the overall algorithm
      (that's the step within which these substeps find themselves).
    </ol>

   <li>
    <p>Otherwise, if <var title="">sign</var> is "positive", return <var
     title="">value</var>, otherwise return 0-<var title="">value</var>.
  </ol>

  <h5 id=ratios><span class=secno>3.2.3.4. </span>Ratios</h5>

  <p class=note>The algorithms described in this section are used by the
   <code><a href="#progress">progress</a></code> and <code><a
   href="#meter">meter</a></code> elements.

  <p>A <dfn id=valid2>valid denominator punctuation character</dfn> is one of
   the characters from the table below. There is <dfn id=a-value
   title="values associated with denominator punctuation characters">a value
   associated with each denominator punctuation character</dfn>, as shown in
   the table below.

  <table>
   <thead>
    <tr>
     <th colspan=2>Denominator Punctuation Character

     <th>Value

   <tbody>
    <tr>
     <td>U+0025 PERCENT SIGN

     <td>&#x0025;

     <td>100

    <tr>
     <td>U+066A ARABIC PERCENT SIGN

     <td>&#x066A;

     <td>100

    <tr>
     <td>U+FE6A SMALL PERCENT SIGN

     <td>&#xFE6A;

     <td>100

    <tr>
     <td>U+FF05 FULLWIDTH PERCENT SIGN

     <td>&#xFF05;

     <td>100

    <tr>
     <td>U+2030 PER MILLE SIGN

     <td>&#x2030;

     <td>1000

    <tr>
     <td>U+2031 PER TEN THOUSAND SIGN

     <td>&#x2031;

     <td>10000
  </table>

  <p>The <dfn id=steps>steps for finding one or two numbers of a ratio in a
   string</dfn> are as follows:

  <ol>
   <li>If the string is empty, then return nothing and abort these steps.

   <li><a href="#find-a">Find a number</a> in the string according to the
    algorithm below, starting at the start of the string.

   <li>If the sub-algorithm in step 2 returned nothing or returned an error
    condition, return nothing and abort these steps.

   <li>Set <var title="">number1</var> to the number returned by the
    sub-algorithm in step 2.

   <li>Starting with the character immediately after the last one examined by
    the sub-algorithm in step 2, skip any characters in the string that are
    in the Unicode character class Zs (this might match zero characters). <a
    href="#refsUNICODE">[UNICODE]</a>

   <li>If there are still further characters in the string, and the next
    character in the string is a <a href="#valid2">valid denominator
    punctuation character</a>, set <var title="">denominator</var> to that
    character.

   <li>If the string contains any other characters in the range U+0030 DIGIT
    ZERO to U+0039 DIGIT NINE, but <var title="">denominator</var> was given
    a value in the step 6, return nothing and abort these steps.

   <li>Otherwise, if <var title="">denominator</var> was given a value in
    step 6, return <var title="">number1</var> and <var
    title="">denominator</var> and abort these steps.

   <li><a href="#find-a">Find a number</a> in the string again, starting
    immediately after the last character that was examined by the
    sub-algorithm in step 2.

   <li>If the sub-algorithm in step 9 returned nothing or an error condition,
    return nothing and abort these steps.

   <li>Set <var title="">number2</var> to the number returned by the
    sub-algorithm in step 9.

   <li>If there are still further characters in the string, and the next
    character in the string is a <a href="#valid2">valid denominator
    punctuation character</a>, return nothing and abort these steps.

   <li>If the string contains any other characters in the range U+0030 DIGIT
    ZERO to U+0039 DIGIT NINE, return nothing and abort these steps.

   <li>Otherwise, return <var title="">number1</var> and <var
    title="">number2</var>.
  </ol>
  <!-- XXX again, this should say "positive number" -->

  <p>The algorithm to <dfn id=find-a>find a number</dfn> is as follows. It is
   given a string and a starting position, and returns either nothing, a
   number, or an error condition.

  <ol>
   <li>Starting at the given starting position, ignore all characters in the
    given string until the first character that is either a U+002E FULL STOP
    or one of the ten characters in the range U+0030 DIGIT ZERO to U+0039
    DIGIT NINE.

   <li>If there are no such characters, return nothing and abort these steps.

   <li>Starting with the character matched in step 1, collect all the
    consecutive characters that are either a U+002E FULL STOP or one of the
    ten characters in the range U+0030 DIGIT ZERO to U+0039 DIGIT NINE, and
    assign this string of one or more characters to <var
    title="">string</var>.

   <li>If <var title="">string</var> contains more than one U+002E FULL STOP
    character then return an error condition and abort these steps.

   <li>Parse <var title="">string</var> according to the <a
    href="#rules1">rules for parsing floating point number values</a>, to
    obtain <var title="">number</var>. This step cannot fail (<var
    title="">string</var> is guarenteed to be a <a href="#valid1">valid
    floating point number</a>).

   <li>Return <var title="">number</var>.
  </ol>

  <h5 id=percentages-and-dimensions><span class=secno>3.2.3.5.
   </span>Percentages and dimensions</h5>

  <p class=big-issue><dfn id=valid3 title="valid non-negative
   percentage">valid non-negative percentages</dfn>, <dfn id=rules2>rules for
   parsing dimension values</dfn> (only used by height/width on img, embed,
   object &mdash; maybe they should do the same as canvas, then this wouldn't
   even be needed)

  <h5 id=lists><span class=secno>3.2.3.6. </span>Lists of integers</h5>

  <p>A <dfn id=valid4>valid list of integers</dfn> is a number of <a
   href="#valid0" title="valid integer">valid integers</a> separated by
   U+002C COMMA characters, with no other characters (e.g. no <a
   href="#space" title="space character">space characters</a>). In addition,
   there might be restrictions on the number of integers that can be given,
   or on the range of values allowed.

  <p>The <dfn id=rules3>rules for parsing a list of integers</dfn> are as
   follows:

  <ol>
   <li>
    <p>Let <var title="">input</var> be the string being parsed.

   <li>
    <p>Let <var title="">position</var> be a pointer into <var
     title="">input</var>, initially pointing at the start of the string.

   <li>
    <p>Let <var title="">numbers</var> be an initially empty list of
     integers. This list will be the result of this algorithm.

   <li>
    <p>If there is a character in the string <var title="">input</var> at
     position <var title="">position</var>, and it is either U+002C COMMA
     character or a U+0020 SPACE character, then advance <var
     title="">position</var> to the next character in <var
     title="">input</var>, or to beyond the end of the string if there are no
     more characters.

   <li>
    <p>If <var title="">position</var> points to beyond the end of <var
     title="">input</var>, return <var title="">numbers</var> and abort.

   <li>
    <p>If the character in the string <var title="">input</var> at position
     <var title="">position</var> is a U+002C COMMA character or a U+0020
     SPACE character, return to step 4.

   <li>
    <p>Let <var title="">negated</var> be false.

   <li>
    <p>Let <var title="">value</var> be 0.

   <li>
    <p>Let <var title="">multiple</var> be 1.

   <li>
    <p>Let <var title="">started</var> be false.

   <li>
    <p>Let <var title="">finished</var> be false.

   <li>
    <p>Let <var title="">bogus</var> be false.

   <li>
    <p><em>Parser:</em> If the character in the string <var
     title="">input</var> at position <var title="">position</var> is:</p>

    <dl
     class=switch><!-- XXX this doesn't quite match what IE does: http://www.hixie.ch/tests/adhoc/html/flow/image-maps/004-demo.html
          I couldn't work out a pattern to IE's results. Let me know if you can see one. -->

     <dt>A U+002D HYPHEN-MINUS character

     <dd>
      <p>Follow these substeps:</p>

      <ol>
       <li>If <var title="">finished</var> is true, skip to the next step in
        the overall set of steps.

       <li>If <var title="">started</var> is true or if <var
        title="">bogus</var> is true, let <var title="">negated</var> be
        false.

       <li>Otherwise, if <var title="">started</var> is false and if <var
        title="">bogus</var> is false, let <var title="">negated</var> be
        true.

       <li>Let <var title="">started</var> be true.
      </ol>

     <dt>A character in the range U+0030 DIGIT ZERO .. U+0039 DIGIT NINE

     <dd>
      <p>Follow these substeps:</p>

      <ol>
       <li>If <var title="">finished</var> is true, skip to the next step in
        the overall set of steps.

       <li>Let <var title="">n</var> be the value of the digit, interpreted
        in base ten, multiplied by <var title="">multiple</var>.

       <li>Add <var title="">n</var> to <var title="">value</var>.

       <li>If <var title="">value</var> is greater than zero, multiply <var
        title="">multiple</var> by ten.

       <li>Let <var title="">started</var> be true.
      </ol>

     <dt>A U+002C COMMA character

     <dt>A U+0020 SPACE character

     <dd>
      <p>Follow these substeps:</p>

      <ol>
       <li>If <var title="">started</var> is false, return the <var
        title="">numbers</var> list and abort.

       <li>If <var title="">negated</var> is true, then negate <var
        title="">value</var>.

       <li>Append <var title="">value</var> to the <var
        title="">numbers</var> list.

       <li>Jump to step 4 in the overall set of steps.
      </ol>

     <dt>A U+002E FULL STOP character

     <dd>
      <p>Follow these substeps:</p>

      <ol>
       <li>Let <var title="">finished</var> be true.
      </ol>

     <dt>Any other character

     <dd>
      <p>Follow these substeps:</p>

      <ol>
       <li>If <var title="">finished</var> is true, skip to the next step in
        the overall set of steps.

       <li>Let <var title="">negated</var> be false.

       <li>Let <var title="">bogus</var> be true.

       <li>If <var title="">started</var> is true, then return the <var
        title="">numbers</var> list, and abort. (The value in <var
        title="">value</var> is not appended to the list first; it is
        dropped.)
      </ol>
    </dl>

   <li>
    <p>Advance <var title="">position</var> to the next character in <var
     title="">input</var>, or to beyond the end of the string if there are no
     more characters.

   <li>
    <p>If <var title="">position</var> points to a character (and not to
     beyond the end of <var title="">input</var>), jump to the big
     <em>Parser</em> step above.

   <li>
    <p>If <var title="">negated</var> is true, then negate <var
     title="">value</var>.

   <li>
    <p>If <var title="">started</var> is true, then append <var
     title="">value</var> to the <var title="">numbers</var> list, return
     that list, and abort.

   <li>
    <p>Return the <var title="">numbers</var> list and abort.
  </ol>

  <h4 id=dates><span class=secno>3.2.4. </span>Dates and times</h4>

  <p>In the algorithms below, the <dfn id=number>number of days in month <var
   title="">month</var> of year <var title="">year</var></dfn> is:
   <em>31</em> if <var title="">month</var> is 1, 3, 5, 7, 8, 10, or 12;
   <em>30</em> if <var title="">month</var> is 4, 6, 9, or 11; <em>29</em> if
   <var title="">month</var> is 2 and <var title="">year</var> is a number
   divisible by 400, or if <var title="">year</var> is a number divisible by
   4 but not by 100; and <em>28</em> otherwise. This takes into account leap
   years in the Gregorian calendar. <a href="#refsGREGORIAN">[GREGORIAN]</a>

  <h5 id=specific><span class=secno>3.2.4.1. </span>Specific moments in time</h5>

  <p>A string is a <dfn id=valid5>valid datetime</dfn> if it has four digits
   (representing the year), a literal hyphen, two digits (representing the
   month), a literal hyphen, two digits (representing the day), optionally
   some spaces, either a literal T or a space, optionally some more spaces,
   two digits (for the hour), a colon, two digits (the minutes), optionally
   the seconds (which, if included, must consist of another colon, two digits
   (the integer part of the seconds), and optionally a decimal point followed
   by one or more digits (for the fractional part of the seconds)),
   optionally some spaces, and finally either a literal Z (indicating the
   time zone is UTC), or, a plus sign or a minus sign followed by two digits,
   a colon, and two digits (for the sign, the hours and minutes of the
   timezone offset respectively); with the month-day combination being a
   valid date in the given year according to the Gregorian calendar, the hour
   values (<var title="">h</var>) being in the range 0&nbsp;&le;&nbsp;<var
   title="">h</var>&nbsp;&le;&nbsp;23, the minute values (<var
   title="">m</var>) in the range 0&nbsp;&le;&nbsp;<var
   title="">m</var>&nbsp;&le;&nbsp;59, and the second value (<var
   title="">s</var>) being in the range 0&nbsp;&le;&nbsp;<var
   title="">h</var>&nbsp;&lt;&nbsp;60. <a
   href="#refsGREGORIAN">[GREGORIAN]</a></p>
  <!--XXX [GREGORIAN] should point to
  <dd id="refsGREGORIAN">[GREGORIAN]</dd>
  <dd>(Non-normative) <cite>Inter Gravissimas</cite>, A. Lilius, C. Clavius. Gregory XIII Papal Bulls, February 1582.</dd>
  -->

  <p>The digits must be characters in the range U+0030 DIGIT ZERO (0) to
   U+0039 DIGIT NINE (9), the hyphens must be a U+002D HYPHEN-MINUS
   characters, the T must be a U+0054 LATIN CAPITAL LETTER T, the colons must
   be U+003A COLON characters, the decimal point must be a U+002E FULL STOP,
   the Z must be a U+005A LATIN CAPITAL LETTER Z, the plus sign must be a
   U+002B PLUS SIGN, and the minus U+002D (same as the hyphen).

  <div class=example>
   <p>The following are some examples of dates written as <a href="#valid5"
    title="valid datetime">valid datetimes</a>.</p>

   <dl>
    <dt>"<code>0037-12-13 00:00 Z</code>"

    <dd>Midnight UTC on the birthday of Nero (the Roman Emperor).

    <dt>"<code>1979-10-14T12:00:00.001-04:00</code>"

    <dd>One millisecond after noon on October 14th 1979, in the time zone in
     use on the east coast of North America during daylight saving time.

    <dt>"<code>8592-01-01 T 02:09 +02:09</code>"

    <dd>Midnight UTC on the 1st of January, 8592. The time zone associated
     with that time is two hours and nine minutes ahead of UTC.
   </dl>

   <p>Several things are notable about these dates:</p>

   <ul>
    <li>Years with fewer than four digits have to be zero-padded. The date
     "37-12-13" would not be a valid date.

    <li>To unambiguously identify a moment in time prior to the introduction
     of the Gregorian calendar, the date has to be first converted to the
     Gregorian calendar from the calendar in use at the time (e.g. from the
     Julian calendar). The date of Nero's birth is the 15th of December 37,
     in the Julian Calendar, which is the 13th of December 37 in the
     Gregorian Calendar.</li>
    <!--
    XXX this might not be true. I can't find a reference that gives
    his birthday with an explicit statement about the calendar being
    used. However, it seems unlikely that it would be given in the
    Gregorian calendar, so I assume sites use the Julian one. -->

    <li>The time and timezone components are not optional.

    <li>Dates before the year 0 or after the year 9999 can't be represented
     as a datetime in this version of HTML.

    <li>Time zones differ based on daylight savings time.
   </ul>
  </div>

  <p class=note>Conformance checkers can use the algorithm below to determine
   if a datetime is a valid datetime or not.

  <p>To <dfn id=datetime-parser>parse a string as a datetime value</dfn>, a
   user agent must apply the following algorithm to the string. This will
   either return a time in UTC, with associated timezone information for
   round tripping or display purposes, or nothing, indicating the value is
   not a <a href="#valid5">valid datetime</a>. If at any point the algorithm
   says that it "fails", this means that it returns nothing.

  <ol>
   <li>
    <p>Let <var title="">input</var> be the string being parsed.

   <li>
    <p>Let <var title="">position</var> be a pointer into <var
     title="">input</var>, initially pointing at the start of the string.

   <li>
    <p><a href="#collect">Collect a sequence of characters</a> in the range
     U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9). If the collected
     sequence is not exactly four characters long, then fail. Otherwise,
     interpret the resulting sequence as a base ten integer. Let that number
     be the <var title="">year</var>.

   <li>
    <p>If <var title="">position</var> is beyond the end of <var
     title="">input</var> or if the character at <var title="">position</var>
     is not a U+002D HYPHEN-MINUS character, then fail. Otherwise, move <var
     title="">position</var> forwards one character.

   <li>
    <p><a href="#collect">Collect a sequence of characters</a> in the range
     U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9). If the collected
     sequence is not exactly two characters long, then fail. Otherwise,
     interpret the resulting sequence as a base ten integer. Let that number
     be the <var title="">month</var>.

   <li>If <var title="">month</var> is not a number in the range
    1&nbsp;&le;&nbsp;<var title="">month</var>&nbsp;&le;&nbsp;12, then fail.

   <li>
    <p>Let <var title="">maxday</var> be the <a href="#number">number of days
     in month <var title="">month</var> of year <var title="">year</var></a>.

   <li>
    <p>If <var title="">position</var> is beyond the end of <var
     title="">input</var> or if the character at <var title="">position</var>
     is not a U+002D HYPHEN-MINUS character, then fail. Otherwise, move <var
     title="">position</var> forwards one character.

   <li>
    <p><a href="#collect">Collect a sequence of characters</a> in the range
     U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9). If the collected
     sequence is not exactly two characters long, then fail. Otherwise,
     interpret the resulting sequence as a base ten integer. Let that number
     be the <var title="">day</var>.

   <li>
    <p>If <var title="">day</var> is not a number in the range
     1&nbsp;&le;&nbsp;<var title="">month</var>&nbsp;&le;&nbsp;<var
     title="">maxday</var>, then fail.

   <li>
    <p><a href="#collect">Collect a sequence of characters</a> that are
     either U+0054 LATIN CAPITAL LETTER T characters or <a href="#space"
     title="space character">space characters</a>. If the collected sequence
     is zero characters long, or if it contains more than one U+0054 LATIN
     CAPITAL LETTER T character, then fail.

   <li>
    <p><a href="#collect">Collect a sequence of characters</a> in the range
     U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9). If the collected
     sequence is not exactly two characters long, then fail. Otherwise,
     interpret the resulting sequence as a base ten integer. Let that number
     be the <var title="">hour</var>.

   <li>If <var title="">hour</var> is not a number in the range
    0&nbsp;&le;&nbsp;<var title="">hour</var>&nbsp;&le;&nbsp;23, then fail.

   <li>
    <p>If <var title="">position</var> is beyond the end of <var
     title="">input</var> or if the character at <var title="">position</var>
     is not a U+003A COLON character, then fail. Otherwise, move <var
     title="">position</var> forwards one character.

   <li>
    <p><a href="#collect">Collect a sequence of characters</a> in the range
     U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9). If the collected
     sequence is not exactly two characters long, then fail. Otherwise,
     interpret the resulting sequence as a base ten integer. Let that number
     be the <var title="">minute</var>.

   <li>If <var title="">minute</var> is not a number in the range
    0&nbsp;&le;&nbsp;<var title="">minute</var>&nbsp;&le;&nbsp;59, then fail.

   <li>
    <p>Let <var title="">second</var> be a string with the value "0".

   <li>
    <p>If <var title="">position</var> is beyond the end of <var
     title="">input</var>, then fail.

   <li>
    <p>If the character at <var title="">position</var> is a U+003A COLON,
     then:</p>

    <ol>
     <li>
      <p>Advance <var title="">position</var> to the next character in <var
       title="">input</var>.

     <li>
      <p>If <var title="">position</var> is beyond the end of <var
       title="">input</var>, or at the last character in <var
       title="">input</var>, or if the next <em>two</em> characters in <var
       title="">input</var> starting at <var title="">position</var> are not
       two characters both in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT
       NINE (9), then fail.

     <li>
      <p><a href="#collect">Collect a sequence of characters</a> that are
       either characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT
       NINE (9) or U+002E FULL STOP characters. If the collected sequence has
       more than one U+002E FULL STOP characters, or if the last character in
       the sequence is a U+002E FULL STOP character, then fail. Otherwise,
       let the collected string be <var title="">second</var> instead of its
       previous value.
    </ol>

   <li>
    <p>Interpret <var title="">second</var> as a base ten number (possibly
     with a fractional part). Let that number be <var title="">second</var>
     instead of the string version.

   <li>If <var title="">second</var> is not a number in the range
    0&nbsp;&le;&nbsp;<var title="">hour</var>&nbsp;&lt;&nbsp;60, then fail.
    (The values 60 and 61 are not allowed: leap seconds cannot be represented
    by datetime values.)

   <li>
    <p>If <var title="">position</var> is beyond the end of <var
     title="">input</var>, then fail.

   <li>
    <p><a href="#skip-whitespace">Skip whitespace.</a>

   <li>
    <p>If the character at <var title="">position</var> is a U+005A LATIN
     CAPITAL LETTER Z, then:</p>

    <ol>
     <li>
      <p>Let <var title="">timezone<sub title="">hours</sub></var> be 0.

     <li>
      <p>Let <var title="">timezone<sub title="">minutes</sub></var> be 0.

     <li>
      <p>Advance <var title="">position</var> to the next character in <var
       title="">input</var>.
    </ol>

   <li>
    <p>Otherwise, if the character at <var title="">position</var> is either
     a U+002B PLUS SIGN ("+") or a U+002D HYPHEN-MINUS ("-"), then:</p>

    <ol>
     <li>
      <p>If the character at <var title="">position</var> is a U+002B PLUS
       SIGN ("+"), let <var title="">sign</var> be "positive". Otherwise,
       it's a U+002D HYPHEN-MINUS ("-"); let <var title="">sign</var> be
       "negative".

     <li>
      <p>Advance <var title="">position</var> to the next character in <var
       title="">input</var>.

     <li>
      <p><a href="#collect">Collect a sequence of characters</a> in the range
       U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9). If the collected
       sequence is not exactly two characters long, then fail. Otherwise,
       interpret the resulting sequence as a base ten integer. Let that
       number be the <var title="">timezone<sub title="">hours</sub></var>.

     <li>If <var title="">timezone<sub title="">hours</sub></var> is not a
      number in the range 0&nbsp;&le;&nbsp;<var title="">timezone<sub
      title="">hours</sub></var>&nbsp;&le;&nbsp;23, then fail.

     <li>If <var title="">sign</var> is "negative", then negate <var
      title="">timezone<sub title="">hours</sub></var>.

     <li>
      <p>If <var title="">position</var> is beyond the end of <var
       title="">input</var> or if the character at <var
       title="">position</var> is not a U+003A COLON character, then fail.
       Otherwise, move <var title="">position</var> forwards one character.

     <li>
      <p><a href="#collect">Collect a sequence of characters</a> in the range
       U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9). If the collected
       sequence is not exactly two characters long, then fail. Otherwise,
       interpret the resulting sequence as a base ten integer. Let that
       number be the <var title="">timezone<sub title="">minutes</sub></var>.

     <li>If <var title="">timezone<sub title="">minutes</sub></var> is not a
      number in the range 0&nbsp;&le;&nbsp;<var title="">timezone<sub
      title="">minutes</sub></var>&nbsp;&le;&nbsp;59, then fail.
    </ol>

   <li>
    <p>If <var title="">position</var> is <em>not</em> beyond the end of <var
     title="">input</var>, then fail.

   <li>
    <p>Let <var title="">time</var> be the moment in time at year <var
     title="">year</var>, month <var title="">month</var>, day <var
     title="">day</var>, hours <var title="">hour</var>, minute <var
     title="">minute</var>, second <var title="">second</var>, adding <var
     title="">timezone<sub title="">hours</sub></var> hours and <var
     title="">timezone<sub title="">minutes</sub></var> minutes. That moment
     in time is a moment in the UTC timezone.

   <li>
    <p>Let <var title="">timezone</var> be <var title="">timezone<sub
     title="">hours</sub></var> hours and <var title="">timezone<sub
     title="">minutes</sub></var> minutes from UTC.

   <li>
    <p>Return <var title="">time</var> and <var title="">timezone</var>.
  </ol>

  <h5 id=vaguer><span class=secno>3.2.4.2. </span>Vaguer moments in time</h5>

  <p>This section defines <dfn id=date-or title="date or time string">date or
   time strings</dfn>. There are two kinds, <dfn id=date-or0 title="date or
   time string in content">date or time strings in content</dfn>, and <dfn
   id=date-or1 title="date or time string in attributes">date or time strings
   in attributes</dfn>. The only difference is in the handling of whitespace
   characters.

  <p>To parse a <a href="#date-or">date or time string</a>, user agents must
   use the following algorithm. A <a href="#date-or">date or time string</a>
   is a <em>valid</em> date or time string if the following algorithm, when
   run on the string, doesn't say the string is invalid.

  <p>The algorithm may return nothing (in which case the string will be
   invalid), or it may return a date, a time, a date and a time, or a date
   and a time and and a timezone. Even if the algorithm returns one or more
   values, the string can still be invalid.

  <ol><!-- INIT -->

   <li>
    <p>Let <var title="">input</var> be the string being parsed.

   <li>
    <p>Let <var title="">position</var> be a pointer into <var
     title="">input</var>, initially pointing at the start of the string.

   <li>
    <p>Let <var title="">results</var> be the collection of results that are
     to be returned (one or more of a date, a time, and a timezone),
     initially empty. If the algorithm aborts at any point, then whatever is
     currently in <var title="">results</var> must be returned as the result
     of the algorithm.
   </li>
   <!-- LEADING WHITESPACE -->

   <li>
    <p>For the "in content" variant: <a href="#skip-">skip Zs characters</a>;
     for the "in attributes" variant: <a href="#skip-whitespace">skip
     whitespace</a>.
   </li>
   <!-- XXX skip whitespace in attribute?
   really? -->
   <!-- YEAR or HOUR -->

   <li>
    <p><a href="#collect">Collect a sequence of characters</a> in the range
     U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9). If the collected
     sequence is empty, then the string is invalid; abort these steps.

   <li>
    <p>Let the sequence of characters collected in the last step be <var
     title="">s</var>.

   <li>
    <p>If <var title="">position</var> is past the end of <var
     title="">input</var>, the string is invalid; abort these steps.

   <li>
    <p>If the character at <var title="">position</var> is <em>not</em> a
     U+003A COLON character, then:</p>
    <!-- DATE -->
    <ol>
     <li>
      <p>If the character at <var title="">position</var> is not a U+002D
       HYPHEN-MINUS ("-") character either, then the string is invalid, abort
       these steps.
     </li>
     <!-- YEAR -->

     <li>
      <p>If the sequence <var title="">s</var> is not exactly four digits
       long, then the string is invalid. (This does not stop the algorithm,
       however.)

     <li>
      <p>Interpret the sequence of characters collected in step 5 as a base
       ten integer, and let that number be <var title="">year</var>.

     <li>
      <p>Advance <var title="">position</var> past the U+002D HYPHEN-MINUS
       ("-") character.
     </li>
     <!-- MONTH -->

     <li>
      <p><a href="#collect">Collect a sequence of characters</a> in the range
       U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9). If the collected
       sequence is empty, then the string is invalid; abort these steps.

     <li>
      <p>If the sequence collected in the last step is not exactly two digits
       long, then the string is invalid.

     <li>
      <p>Interpret the sequence of characters collected two steps ago as a
       base ten integer, and let that number be <var title="">month</var>.

     <li>If <var title="">month</var> is not a number in the range
      1&nbsp;&le;&nbsp;<var title="">month</var>&nbsp;&le;&nbsp;12, then the
      string is invalid, abort these steps.

     <li>
      <p>Let <var title="">maxday</var> be the <a href="#number">number of
       days in month <var title="">month</var> of year <var
       title="">year</var></a>.

     <li>
      <p>If <var title="">position</var> is past the end of <var
       title="">input</var>, or if the character at <var
       title="">position</var> is <em>not</em> a U+002D HYPHEN-MINUS ("-")
       character, then the string is invalid, abort these steps. Otherwise,
       advance <var title="">position</var> to the next character.
     </li>
     <!-- DAY -->

     <li>
      <p><a href="#collect">Collect a sequence of characters</a> in the range
       U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9). If the collected
       sequence is empty, then the string is invalid; abort these steps.

     <li>
      <p>If the sequence collected in the last step is not exactly two digits
       long, then the string is invalid.

     <li>
      <p>Interpret the sequence of characters collected two steps ago as a
       base ten integer, and let that number be <var title="">day</var>.

     <li>
      <p>If <var title="">day</var> is not a number in the range
       1&nbsp;&le;&nbsp;<var title="">day</var>&nbsp;&le;&nbsp;<var
       title="">maxday</var>, then the string is invalid, abort these steps.

     <li>
      <p>Add the date represented by <var title="">year</var>, <var
       title="">month</var>, and <var title="">day</var> to the <var
       title="">results</var>.
     </li>
     <!-- WHITESPACE -->

     <li>
      <p>For the "in content" variant: <a href="#skip-">skip Zs
       characters</a>; for the "in attributes" variant: <a
       href="#skip-whitespace">skip whitespace</a>.

     <li>
      <p>If the character at <var title="">position</var> is a U+0054 LATIN
       CAPITAL LETTER T, then move <var title="">position</var> forwards one
       character.

     <li>
      <p>For the "in content" variant: <a href="#skip-">skip Zs
       characters</a>; for the "in attributes" variant: <a
       href="#skip-whitespace">skip whitespace</a>.
     </li>
     <!-- at this point, if <var title="">position</var> points to a
     number, we know that we passed at least one space or a T, because
     otherwise the number would have been slurped up in the last
     "collect" step. -->
     <!-- HOUR -->

     <li>
      <p><a href="#collect">Collect a sequence of characters</a> in the range
       U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9). If the collected
       sequence is empty, then the string is invalid; abort these steps.

     <li>
      <p>Let <var title="">s</var> be the sequence of characters collected in
       the last step.
    </ol>
   </li>
   <!-- TIME -->

   <li>
    <p>If <var title="">s</var> is not exactly two digits long, then the
     string is invalid.

   <li>
    <p>Interpret the sequence of characters collected two steps ago as a base
     ten integer, and let that number be <var title="">hour</var>.

   <li>
    <p>If <var title="">hour</var> is not a number in the range
     0&nbsp;&le;&nbsp;<var title="">hour</var>&nbsp;&le;&nbsp;23, then the
     string is invalid, abort these steps.

   <li>
    <p>If <var title="">position</var> is past the end of <var
     title="">input</var>, or if the character at <var
     title="">position</var> is <em>not</em> a U+003A COLON character, then
     the string is invalid, abort these steps. Otherwise, advance <var
     title="">position</var> to the next character.
   </li>
   <!-- MINUTE -->

   <li>
    <p><a href="#collect">Collect a sequence of characters</a> in the range
     U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9). If the collected
     sequence is empty, then the string is invalid; abort these steps.

   <li>
    <p>If the sequence collected in the last step is not exactly two digits
     long, then the string is invalid.

   <li>
    <p>Interpret the sequence of characters collected two steps ago as a base
     ten integer, and let that number be <var title="">minute</var>.

   <li>
    <p>If <var title="">minute</var> is not a number in the range
     0&nbsp;&le;&nbsp;<var title="">minute</var>&nbsp;&le;&nbsp;59, then the
     string is invalid, abort these steps.
   </li>
   <!-- SECOND -->

   <li>
    <p>Let <var title="">second</var> be 0. It may be changed to another
     value in the next step.

   <li>
    <p>If <var title="">position</var> is not past the end of <var
     title="">input</var> and the character at <var title="">position</var>
     is a U+003A COLON character, then:</p>

    <ol>
     <li>
      <p><a href="#collect">Collect a sequence of characters</a> that are
       either characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT
       NINE (9) or are U+002E FULL STOP. If the collected sequence is empty,
       or contains more than one U+002E FULL STOP character, then the string
       is invalid; abort these steps.

     <li>
      <p>If the first character in the sequence collected in the last step is
       not in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9), then
       the string is invalid.

     <li>
      <p>Interpret the sequence of characters collected two steps ago as a
       base ten number (possibly with a fractional part), and let that number
       be <var title="">second</var>.

     <li>
      <p>If <var title="">second</var> is not a number in the range
       0&nbsp;&le;&nbsp;<var title="">minute</var>&nbsp;&lt;&nbsp;60, then
       the string is invalid, abort these steps.
    </ol>

   <li>
    <p>Add the time represented by <var title="">hour</var>, <var
     title="">minute</var>, and <var title="">second</var> to the <var
     title="">results</var>.
   </li>
   <!-- TIME ZONE -->

   <li>
    <p>If <var title="">results</var> has both a date and a time, then:</p>

    <ol>
     <li>
      <p>For the "in content" variant: <a href="#skip-">skip Zs
       characters</a>; for the "in attributes" variant: <a
       href="#skip-whitespace">skip whitespace</a>.

     <li>
      <p>If <var title="">position</var> is past the end of <var
       title="">input</var>, then skip to the next step in the overall set of
       steps.</p>
      <!-- UTC -->

     <li>
      <p>Otherwise, if the character at <var title="">position</var> is a
       U+005A LATIN CAPITAL LETTER Z, then:</p>

      <ol>
       <li>
        <p>Add the timezone corresponding to UTC (zero offset) to the <var
         title="">results</var>.

       <li>
        <p>Advance <var title="">position</var> to the next character in <var
         title="">input</var>.

       <li>
        <p>Skip to the next step in the overall set of steps.
      </ol>
     </li>
     <!-- EXPLICIT TIMEZONE OFFSET -->

     <li>
      <p>Otherwise, if the character at <var title="">position</var> is
       either a U+002B PLUS SIGN ("+") or a U+002D HYPHEN-MINUS ("-"), then:</p>

      <ol><!-- SIGN -->

       <li>
        <p>If the character at <var title="">position</var> is a U+002B PLUS
         SIGN ("+"), let <var title="">sign</var> be "positive". Otherwise,
         it's a U+002D HYPHEN-MINUS ("-"); let <var title="">sign</var> be
         "negative".
       </li>
       <!-- HOURS -->

       <li>
        <p>Advance <var title="">position</var> to the next character in <var
         title="">input</var>.

       <li>
        <p><a href="#collect">Collect a sequence of characters</a> in the
         range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9). If the
         collected sequence is not exactly two characters long, then the
         string is invalid.

       <li>
        <p>Interpret the sequence collected in the last step as a base ten
         number, and let that number be <var title="">timezone<sub
         title="">hours</sub></var>.

       <li>If <var title="">timezone<sub title="">hours</sub></var> is not a
        number in the range 0&nbsp;&le;&nbsp;<var title="">timezone<sub
        title="">hours</sub></var>&nbsp;&le;&nbsp;23, then the string is
        invalid; abort these steps.

       <li>If <var title="">sign</var> is "negative", then negate <var
        title="">timezone<sub title="">hours</sub></var>.

       <li>
        <p>If <var title="">position</var> is beyond the end of <var
         title="">input</var> or if the character at <var
         title="">position</var> is not a U+003A COLON character, then the
         string is invalid; abort these steps. Otherwise, move <var
         title="">position</var> forwards one character.
       </li>
       <!-- MINUTES -->

       <li>
        <p><a href="#collect">Collect a sequence of characters</a> in the
         range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9). If the
         collected sequence is not exactly two characters long, then the
         string is invalid.

       <li>
        <p>Interpret the sequence collected in the last step as a base ten
         number, and let that number be <var title="">timezone<sub
         title="">minutes</sub></var>.

       <li>If <var title="">timezone<sub title="">minutes</sub></var> is not
        a number in the range 0&nbsp;&le;&nbsp;<var title="">timezone<sub
        title="">minutes</sub></var>&nbsp;&le;&nbsp;59, then the string is
        invalid; abort these steps.

       <li>
        <p>Add the timezone corresponding to an offset of <var
         title="">timezone<sub title="">hours</sub></var> hours and <var
         title="">timezone<sub title="">minutes</sub></var> minutes to the
         <var title="">results</var>.

       <li>
        <p>Skip to the next step in the overall set of steps.
      </ol>

     <li>
      <p>Otherwise, the string is invalid; abort these steps.
    </ol>

   <li>
    <p>For the "in content" variant: <a href="#skip-">skip Zs characters</a>;
     for the "in attributes" variant: <a href="#skip-whitespace">skip
     whitespace</a>.

   <li>
    <p>If <var title="">position</var> is <em>not</em> past the end of <var
     title="">input</var>, then the string is invalid.</p>

   <li>
    <p>Abort these steps (the string is parsed).
  </ol>

  <h4 id=time-offsets><span class=secno>3.2.5. </span>Time offsets</h4>

  <p class=big-issue><dfn id=valid6>valid time offset</dfn>, <dfn
   id=rules4>rules for parsing time offsets</dfn>, <dfn id=time-offset>time
   offset serialisation rules</dfn>; in the format "5d4h3m2s1ms" or "3m 9.2s"
   or "00:00:00.00" or similar.

  <h4 id=tokens><span class=secno>3.2.6. </span>Tokens</h4>

  <p>A <dfn id=set-of>set of space-separated tokens</dfn> is a set of zero or
   more words separated by one or more <a href="#space" title="space
   character">space characters</a>, where words consist of any string of one
   or more characters, none of which are <a href="#space" title="space
   character">space characters</a>.

  <p>A string containing a <a href="#set-of">set of space-separated
   tokens</a> may have leading or trailing <a href="#space" title="space
   character">space characters</a>.

  <p>An <dfn id=unordered>unordered set of space-separated tokens</dfn> is a
   <a href="#set-of">set of space-separated tokens</a> where none of the
   words are duplicated.

  <p>An <dfn id=ordered>ordered set of unique space-separated tokens</dfn> is
   a <a href="#set-of">set of space-separated tokens</a> where none of the
   words are duplicated but where the order of the tokens is meaningful.

  <p>When a user agent has to <dfn id=split>split a string on spaces</dfn>,
   it must use the following algorithm:

  <ol>
   <li>
    <p>Let <var title="">input</var> be the string being parsed.

   <li>
    <p>Let <var title="">position</var> be a pointer into <var
     title="">input</var>, initially pointing at the start of the string.

   <li>
    <p>Let <var title="">tokens</var> be a list of tokens, initially empty.

   <li>
    <p><a href="#skip-whitespace">Skip whitespace</a>

   <li>
    <p>While <var title="">position</var> is not past the end of <var
     title="">input</var>:</p>

    <ol>
     <li>
      <p><a href="#collect">Collect a sequence of characters</a> that are not
       <a href="#space" title="space character">space characters</a>.

     <li>
      <p>Add the string collected in the previous step to <var
       title="">tokens</var>.

     <li>
      <p><a href="#skip-whitespace">Skip whitespace</a>
    </ol>

   <li>
    <p>Return <var title="">tokens</var>.
  </ol>

  <p>When a user agent has to <dfn id=remove0>remove a token from a
   string</dfn>, it must use the following algorithm:

  <ol>
   <li>
    <p>Let <var title="">input</var> be the string being modified.

   <li>
    <p>Let <var title="">token</var> be the token being removed. It will not
     contain any <a href="#space" title="space character">space
     characters</a>.

   <li>
    <p>Let <var title="">output</var> be the output string, initially empty.

   <li>
    <p>Let <var title="">position</var> be a pointer into <var
     title="">input</var>, initially pointing at the start of the string.

   <li>
    <p>If <var title="">position</var> is beyond the end of <var
     title="">input</var>, set the string being modified to <var
     title="">output</var>, and abort these steps.

   <li>
    <p>If the character at <var title="">position</var> is a <a
     href="#space">space character</a>:

    <ol>
     <li>
      <p>Append the character at <var title="">position</var> to the end of
       <var title="">output</var>.

     <li>
      <p>Increment <var title="">position</var> so it points at the next
       character in <var title="">input</var>.

     <li>
      <p>Return to step 5 in the overall set of steps.
    </ol>

   <li>
    <p>Otherwise, the character at <var title="">position</var> is the first
     character of a token. <a href="#collect">Collect a sequence of
     characters</a> that are not <a href="#space" title="space
     character">space characters</a>, and let that be <var title="">s</var>.

   <li>
    <p>If <var title="">s</var> is exactly equal to <var
     title="">token</var>, then:</p>

    <ol>
     <li>
      <p><a href="#skip-whitespace">Skip whitespace</a> (in <var
       title="">input</var>).

     <li>
      <p>Remove any <a href="#space" title="space character">space
       characters</a> currently at the end of <var title="">output</var>.

     <li>
      <p>If <var title="">position</var> is not past the end of <var
       title="">input</var>, and <var title="">output</var> is not the empty
       string, append a single U+0020 SPACE character at the end of <var
       title="">output</var>.
    </ol>

   <li>
    <p>Otherwise, append <var title="">s</var> to the end of <var
     title="">output</var>.

   <li>
    <p>Return to step 6 in the overall set of steps.
  </ol>

  <p class=note>This causes any occurrences of the token to be removed from
   the string, and any spaces that were surrounding the token to be collapsed
   to a single space, except at the start and end of the string, where such
   spaces are removed.

  <h4 id=keywords><span class=secno>3.2.7. </span>Keywords and enumerated
   attributes</h4>

  <p>Some attributes are defined as taking one of a finite set of keywords.
   Such attributes are called <dfn id=enumerated title="enumerated
   attribute">enumerated attributes</dfn>. The keywords are each defined to
   map to a particular <em>state</em> (several keywords might map to the same
   state, in which case some of the keywords are synonyms of each other;
   additionally, some of the keywords can be said to be non-conforming, and
   are only in the specification for historical reasons). In addition, two
   default states can be given. The first is the <em>invalid value
   default</em>, the second is the <em>missing value default</em>.

  <p>If an enumerated attribute is specified, the attribute's value must be
   one of the given keywords that are not said to be non-conforming, with no
   leading or trailing whitespace. The keyword may use any mix of uppercase
   and lowercase letters.<!-- XXX should
  say "uppercase and lowercase ASCII letters" or some such -->

  <p>When the attribute is specified, if its value
   <span>case-insensitively</span><!-- XXX ascii case folding --> matches one
   of the given keywords then that keyword's state is the state that the
   attribute represents. If the attribute value matches none of the given
   keywords, but the attribute has an <em>invalid value default</em>, then
   the attribute represents that state. Otherwise, if the attribute value
   matches none of the keywords but there is a <em>missing value default</em>
   state defined, then <em>that</em> is the state represented by the
   attribute. Otherwise, there is no default, and invalid values must simply
   be ignored.

  <p>When the attribute is <em>not</em> specified, if there is a <em>missing
   value default</em> state defined, then that is the state represented by
   the (missing) attribute. Otherwise, the absence of the attribute means
   that there is no state represented.

  <p class=note>The empty string can be one of the keywords in some cases.
   For example the <code title=attr-contenteditable><a
   href="#contenteditable0">contenteditable</a></code> attribute has two
   states: <em>true</em>, matching the <code title="">true</code> keyword and
   the empty string, <em>false</em>, matching <code title="">false</code> and
   all other keywords (it's the <em>invalid value default</em>). It could
   further be thought of as having a third state <em>inherit</em>, which
   would be the default when the attribute is not specified at all (the
   <em>missing value default</em>), but for various reasons that isn't the
   way this specification actually defines it.

  <h4 id=syntax-references><span class=secno>3.2.8. </span>References</h4>

  <p>A <dfn id=valid7>valid hashed ID reference</dfn> to an element of type
   <var title="">type</var> is a string consisting of a U+0023 NUMBER SIGN
   (<code title="">#</code>) character followed by a string which exactly
   matches the value of the <code title=attr-id><a href="#id">id</a></code>
   attribute of an element in the document with type <var
   title="">type</var>.

  <p>The <dfn id=rules5>rules for parsing a hashed ID reference</dfn> to an
   element of type <var title="">type</var> are as follows:

  <ol>
   <li>
    <p>If the string being parsed does not contain a U+0023 NUMBER SIGN
     character, or if the first such character in the string is the last
     character in the string, then return null and abort these steps.

   <li>
    <p>Let <var title="">s</var> be the string from the character immediately
     after the first U+0023 NUMBER SIGN character in the string being parsed
     up to the end of that string.

   <li>
    <p>Return the first element of type <var title="">type</var> that has an
     <code title=attr-id><a href="#id">id</a></code> or <code
     title="">name</code> attribute whose value case-insensitively matches
     <var title="">s</var>.
  </ol>

  <h3 id=documents0><span class=secno>3.3. </span>Documents and document
   fragments</h3>

  <h4 id=semantics0><span class=secno>3.3.1. </span>Semantics</h4>

  <p>Elements, attributes, and attribute values in HTML are defined (by this
   specification) to have certain meanings (semantics). For example, the
   <code><a href="#ol">ol</a></code> element represents an ordered list, and
   the <code title=lang>lang</code> attribute represents the language of the
   content.

  <p>Authors must only use elements, attributes, and attribute values for
   their appropriate semantic purposes.

  <div class=example>
   <p>For example, the following document is non-conforming, despite being
    syntactically correct:</p>

   <pre>&lt;!DOCTYPE html&gt;
&lt;html lang="en-GB"&gt;
 &lt;head&gt; &lt;title&gt; Demonstration &lt;/title&gt; &lt;/head&gt;
 &lt;body&gt;
  &lt;table&gt;
   &lt;tr&gt; &lt;td&gt; My favourite animal is the cat. &lt;/td&gt; &lt;/tr&gt;
   &lt;tr&gt;
    &lt;td&gt;
     &mdash;&lt;a href="http://example.org/~ernest/"&gt;&lt;cite&gt;Ernest&lt;/cite&gt;&lt;/a&gt;,
     in an essay from 1992
    &lt;/td&gt;
   &lt;/tr&gt;
  &lt;/table&gt;
 &lt;/body&gt;
&lt;/html&gt;</pre>

   <p>...because the data placed in the cells is clearly not tabular data. A
    corrected version of this document might be:</p>

   <pre>&lt;!DOCTYPE html&gt;
&lt;html lang="en-GB"&gt;
 &lt;head&gt; &lt;title&gt; Demonstration &lt;/title&gt; &lt;/head&gt;
 &lt;body&gt;
  &lt;blockquote&gt;
   &lt;p&gt; My favourite animal is the cat. &lt;/p&gt;
  &lt;/blockquote&gt;
  &lt;p&gt;
   &mdash;&lt;a href="http://example.org/~ernest/"&gt;&lt;cite&gt;Ernest&lt;/cite&gt;&lt;/a&gt;,
   in an essay from 1992
  &lt;/p&gt;
 &lt;/body&gt;
&lt;/html&gt;</pre>

   <p>This next document fragment, intended to represent the heading of a
    corporate site, is similarly non-conforming because the second line is
    not intended to be a heading of a subsection, but merely a subheading or
    subtitle (a subordinate heading for the same section).</p>

   <pre>&lt;body&gt;
 &lt;h1&gt;ABC Company&lt;/h1&gt;
 &lt;h2&gt;Leading the way in widget design since 1432&lt;/h2&gt;
 ...</pre>

   <p>The <code><a href="#header">header</a></code> element should be used in
    these kinds of situations:</p>

   <pre>&lt;body&gt;
 &lt;header&gt;
  &lt;h1&gt;ABC Company&lt;/h1&gt;
  &lt;h2&gt;Leading the way in widget design since 1432&lt;/h2&gt;
 &lt;/header&gt;
 ...</pre>
  </div>

  <p>Through scripting and using other mechanisms, the values of attributes,
   text, and indeed the entire structure of the document may change
   dynamically while a user agent is processing it. The semantics of a
   document at an instant in time are those represented by the state of the
   document at that instant in time, and the semantics of a document can
   therefore change over time. User agents must update their presentation of
   the document as this occurs.

  <p class=example>HTML has a <code><a href="#progress">progress</a></code>
   element that describes a progress bar. If its "value" attribute is
   dynamically updated by a script, the UA would update the rendering to show
   the progress changing.

  <h4 id=structure0><span class=secno>3.3.2. </span>Structure</h4>

  <p>All the elements in this specification have a defined content model,
   which describes what nodes are allowed inside the elements, and thus what
   the structure of an HTML document or fragment must look like. Authors must
   only put elements inside an element if that element allows them to be
   there according to its content model.

  <p class=note>As noted in the conformance and terminology sections, for the
   purposes of determining if an element matches its content model or not, <a
   href="#text-node" title="text node"><code>CDATASection</code> nodes in the
   DOM are treated as equivalent to <code>Text</code> nodes</a>, and <a
   href="#entity-references">entity reference nodes are treated as if they
   were expanded in place</a>.

  <p>The <a href="#space" title="space character">space characters</a> are
   always allowed between elements. User agents represent these characters
   between elements in the source markup as text nodes in the
   DOM.<!-- not a conf criteria since the parser now requires this
  -->
   Empty <a href="#text-node" title="text node">text nodes</a> and <a
   href="#text-node" title="text node">text nodes</a> consisting of just
   sequences of those characters are considered <dfn
   id=inter-element>inter-element whitespace</dfn>.

  <p><a href="#inter-element">Inter-element whitespace</a>, comment nodes,
   and processing instruction nodes must be ignored when establishing whether
   an element matches its content model or not, and must be ignored when
   following algorithms that define document and element semantics.

  <p>An element <var title="">A</var> is said to be <dfn
   id=preceeded>preceeded or followed</dfn> by a second element <var
   title="">B</var> if <var title="">A</var> and <var title="">B</var> have
   the same parent node and there are no other element nodes or text nodes
   (other than <a href="#inter-element">inter-element whitespace</a>) between
   them.

  <p>Authors must only use <a href="#elements1">elements in the HTML
   namespace</a> in the contexts where they are allowed, as defined for each
   element. For XML compound documents, these contexts could be inside
   elements from other namespaces, if those elements are defined as providing
   the relevant contexts.

  <div class=example>
   <p>The SVG specification defines the SVG <code>foreignObject</code>
    element as allowing foreign namespaces to be included, thus allowing
    compound documents to be created by inserting subdocument content under
    that element. <em>This</em> specification defines the XHTML <code><a
    href="#html">html</a></code> element as being allowed where subdocument
    fragments are allowed in a compound document. Together, these two
    definitions mean that placing an XHTML <code><a
    href="#html">html</a></code> element as a child of an SVG
    <code>foreignObject</code> element is conforming.</p>
  </div>

  <h4 id=kinds><span class=secno>3.3.3. </span>Kinds of elements</h4>

  <p>Each element in HTML falls into zero or more categories that group
   elements with similar characteristics together. This specification uses
   the following categories:

  <ul class=brief>
   <li><a href="#metadata">Metadata elements</a>

   <li><a href="#sectioning">Sectioning elements</a>

   <li><a href="#block-level0">Block-level elements</a>

   <li><a href="#strictly">Strictly inline-level content</a>

   <li><a href="#structured">Structured inline-level elements</a>

   <li><a href="#interactive1">Interactive elements</a>

   <li><span>Form control elements</span>
  </ul>
  <!-- XXX check that all the above got a section defining them,
  however briefly -->
  <!-- XXX check that the element definitions also link to those
  sections -->

  <p>Some elements have unique requirements and do not fit into any
   particular category.

  <p>In addition, some elements represent various common concepts; for
   example, some elements represent <span>paragraphs</span>.

  <h5 id=block-level><span class=secno>3.3.3.1. </span><dfn
   id=block-level0>Block-level elements</dfn></h5>

  <p>Block-level elements are used for structural grouping of page content.

  <p>There are several kinds of block-level elements:

  <ul>
   <li>Some can only contain other block-level elements: <code><a
    href="#blockquote">blockquote</a></code>, <code><a
    href="#section">section</a></code>, <code><a
    href="#article">article</a></code>, <code><a
    href="#header">header</a></code>.

   <li>Some can only contain <a href="#inline-level0">inline-level
    content</a>: <code><a href="#p">p</a></code>, <code><a
    href="#h1">h1</a></code>-<code><a href="#h6">h6</a></code>, <code><a
    href="#address">address</a></code>.

   <li>Some can contain either block-level elements or <a
    href="#inline-level0">inline-level content</a> (but not both): <code><a
    href="#nav">nav</a></code>, <code><a href="#aside">aside</a></code>,
    <code><a href="#footer">footer</a></code>, <code><a
    href="#div">div</a></code>.

   <li>Finally, some have very specific content models: <code><a
    href="#ul">ul</a></code>, <code><a href="#ol">ol</a></code>, <code><a
    href="#dl">dl</a></code>, <code><a href="#table">table</a></code>,
    <code><a href="#script0">script</a></code>.
  </ul>

  <p>There are also elements that seem to be block-level but aren't, such as
   <code><a href="#body0">body</a></code>, <code><a href="#li">li</a></code>,
   <code><a href="#dt">dt</a></code>, <code><a href="#dd">dd</a></code>, and
   <code><a href="#td">td</a></code>. These elements are allowed only in
   specific places, not simply anywhere that block-level elements are
   allowed.

  <p>Some block-level elements play multiple roles. For instance, the
   <code><a href="#script0">script</a></code> elements is allowed inside
   <code><a href="#head">head</a></code> elements and can also be used as <a
   href="#inline-level0">inline-level content</a>. Similarly, the <code><a
   href="#ul">ul</a></code>, <code><a href="#ol">ol</a></code>, <code><a
   href="#dl">dl</a></code>, <code><a href="#table">table</a></code>, and
   <code><a href="#blockquote">blockquote</a></code> elements play dual roles
   as both block-level and inline-level elements.

  <h5 id=inline-level><span class=secno>3.3.3.2. </span><dfn
   id=inline-level0>Inline-level content</dfn></h5>

  <p>Inline-level content consists of text and various elements to annotate
   the text, as well as some <a href="#embedded0">embedded content</a> (such
   as images or sound clips).

  <p>Inline-level content comes in various types:

  <dl>
   <dt><dfn id=strictly>Strictly inline-level content</dfn>

   <dd>Text, <a href="#embedded0">embedded content</a>, and elements that
    annotate the text without introducing structural grouping. For example:
    <code><a href="#a">a</a></code>, <code><a href="#meter">meter</a></code>,
    <code><a href="#img">img</a></code>. Elements used in contexts allowing
    only strictly inline-level content must not have any descendants that are
    anything other than strictly inline-level content.

   <dt><dfn id=structured>Structured inline-level elements</dfn>

   <dd>Block-level elements that can also be used as inline-level content.
    For example: <code><a href="#ol">ol</a></code>, <code><a
    href="#blockquote">blockquote</a></code>, <code><a
    href="#table">table</a></code>.
  </dl>

  <p>Some elements are defined to have as a content model <dfn
   id=significant>significant inline content</dfn>. This means that at least
   one descendant of the element must be <a href="#significant0">significant
   text</a> or <a href="#embedded0">embedded content</a>.

  <p>Unless an element's content model explicitly states that it must contain
   <a href="#significant">significant inline content</a>, simply having no <a
   href="#text-node" title="text node">text nodes</a> and no elements
   satisfies an element whose content model is some kind of inline content.

  <p><dfn id=significant0>Significant text</dfn>, for the purposes of
   determining the presence of <a href="#significant">significant inline
   content</a>, consists of any character other than those falling in the <a
   href="http://unicode.org/Public/UNIDATA/UCD.html#General_Category_Values">Unicode
   categories</a> Zs, Zl, Zp, Cc, and Cf. <a
   href="#refsUNICODE">[UNICODE]</a>

  <div class=example>
   <p>The following three paragraphs are non-conforming because their content
    model is not satisfied (they all count as empty).</p>

   <pre>
&lt;p&gt;&lt;/p&gt;
&lt;p&gt;&lt;em&gt;&amp;#x00A0;&lt;/em&gt;&lt;/p&gt;
&lt;p&gt;
 &lt;ol&gt;
  &lt;li&gt;&lt;/li&gt;
 &lt;/ol&gt;
&lt;/p&gt;
</pre>
  </div>

  <p><dfn id=embedded0>Embedded content</dfn> consists of elements that
   introduce content from other resources into the document, for example
   <code><a href="#img">img</a></code>. Embedded content elements can have
   <dfn id=fallback>fallback content</dfn>: content that is to be used when
   the external resource cannot be used (e.g. because it is of an unsupported
   format). The element definitions state what the fallback is, if any.

  <h5 id=transparent><span class=secno>3.3.3.3. </span>Transparent content
   models</h5>

  <p>Some elements are described as <dfn id=transparent0>transparent</dfn>;
   they have "transparent" as their content model. Some elements are
   described as <dfn id=semi-transparent>semi-transparent</dfn>; this means
   that part of their content model is "transparent" but that is not the only
   part of the content model that must be satisfied.

  <p>When a content model includes a part that is "transparent", those parts
   must only contain content that would still be conformant if all
   transparent and semi-transparent elements in the tree were replaced, in
   their parent element, by the children in the "transparent" part of their
   content model, retaining order.

  <p>When a transparent or semi-transparent element has no parent, then the
   part of its content model that is "transparent" must instead be treated as
   zero or more <a href="#block-level0">block-level elements</a>, or <a
   href="#inline-level0">inline-level content</a> (but not both).

  <h5 id=determining><span class=secno>3.3.3.4. </span><dfn
   id=determining0>Determining if a particular element contains block-level
   elements or inline-level content</dfn></h5>

  <p>Some elements are defined to have content models that allow either <a
   href="#block-level0">block-level elements</a> or <a
   href="#inline-level0">inline-level content</a>, but not both. For example,
   the <code><a href="#aside">aside</a></code> and <code><a
   href="#li">li</a></code> elements.

  <p>To establish whether such an element is being used as a block-level
   container or as an inline-level container, for example in order to
   determine if a document conforms to these requirements, user agents must
   look at the element's child nodes. If any of the child nodes are not
   allowed in block-level contexts, then the element is being used for <a
   href="#inline-level0">inline-level content</a>. If all the child nodes are
   allowed in a block-level context, then the element is being used for <a
   href="#block-level0">block-level elements</a>.

  <p>Whenever this search would examine a <a
   href="#transparent0">transparent</a> element, the element's own child
   nodes must be examined instead, potentially recursing further if any of
   those are themselves transparent.

  <div class=example>
   <p>For instance, in the following (non-conforming) XML fragment, the
    <code><a href="#li">li</a></code> element is being used as an
    inline-level element container, because the <code><a
    href="#meta0">meta</a></code> element is not allowed in a block-level
    context. (It doesn't matter, for the purposes of determining whether it
    is an inline-level or block-level context, that the <code><a
    href="#meta0">meta</a></code> element is not allowed in inline-level
    contexts either.)</p>

   <pre>&lt;ol&gt;
 &lt;li&gt;
  &lt;p&gt; Hello World &lt;/p&gt;
  &lt;meta title="this is an invalid example"/&gt;
 &lt;/li&gt;
&lt;/ol&gt;
</pre>

   <p>In the following fragment, the <code><a href="#aside">aside</a></code>
    element is being used as a block-level container, because even though all
    the elements it contains could be considered inline-level elements, there
    are no nodes that can only be considered inline-level.</p>

   <pre>&lt;aside&gt;
 &lt;ol&gt;
  &lt;li&gt; ... &lt;/li&gt;
 &lt;/ol&gt;
 &lt;ul&gt;
  &lt;li&gt; ... &lt;/li&gt;
 &lt;/ul&gt;
&lt;/aside&gt;</pre>

   <p>On the other hand, in the following similar fragment, the <code><a
    href="#aside">aside</a></code> element is an inline-level container,
    because the text ("Foo") can only be considered inline-level.</p>

   <pre>&lt;aside&gt;
 &lt;ol&gt;
  &lt;li&gt; ... &lt;/li&gt;
 &lt;/ol&gt;
 Foo
&lt;/aside&gt;</pre>
  </div>

  <h5 id=interactive0><span class=secno>3.3.3.5. </span><dfn
   id=interactive1>Interactive elements</dfn></h5>
  <!-- Don't change the above <dfn> or the text below without checking
  all cross-references. Some of them refer specifically to the
  activation behavior stuff. -->

  <p class=big-issue>Parts of this section should eventually be moved to DOM3
   Events.</p>
  <!-- but see comment above -->
  <!--
TESTS:
http://software.hixie.ch/utilities/js/live-dom-viewer/?%3C%21DOCTYPE%20html%3E%0A%3Cp%20tabindex%3D1%3Etest%20%3Ca%20href%3D%22%22%3E%20%3Cem%3Etest%3C/em%3E%20%3C/a%3E%0A%3Cscript%3E%0A%20function%20test%20%28e%29%20%7B%20w%28e.type%20+%20%27%20on%20%27%20+%20e.target.tagName%20+%20%27%20through%20%27%20+%20e.currentTarget.tagName%29%3B%20%7D%0A%20document.getElementsByTagName%28%27a%27%29%5B0%5D.addEventListener%28%27click%27%2C%20test%2C%20false%29%3B%0A%20document.getElementsByTagName%28%27a%27%29%5B0%5D.addEventListener%28%27DOMActivate%27%2C%20test%2C%20false%29%3B%0A%20document.getElementsByTagName%28%27p%27%29%5B0%5D.addEventListener%28%27click%27%2C%20test%2C%20false%29%3B%0A%20document.getElementsByTagName%28%27p%27%29%5B0%5D.addEventListener%28%27DOMActivate%27%2C%20test%2C%20false%29%3B%0A%3C/script%3E%0A
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-->

  <p>Certain elements in HTML can be activated, for instance <code><a
   href="#a">a</a></code> elements, <code>button</code> elements, or
   <code>input</code> elements when their <code>type</code> attribute is set
   to <code>radio</code>. Activation of those elements can happen in various
   (UA-defined) ways, for instance via the mouse or keyboard.

  <p>When activation is performed via some method other than clicking the
   pointing device, the default action of the event that triggers the
   activation must, instead of being activating the element directly, be to
   <a href="#firing">fire a <code title="">click</code> event</a> on the same
   element.

  <p>The default action of this <code title=event-click>click</code> event,
   or of the real <code title=event-click>click</code> event if the element
   was activated by clicking a pointing device, must be to <span title="fire
   a DOMActivate event">fire a further <code
   title=event-DOMActivate>DOMActivate</code> event</span> at the same
   element, whose own default action is to go through all the elements the
   <code title=event-DOMActivate>DOMActivate</code> event bubbled through
   (starting at the target node and going towards the <code>Document</code>
   node), looking for an element with an <a href="#activation0">activation
   behavior</a>; the first element, in reverse tree order, to have one, must
   have its activation behavior executed.

  <p class=note>The above doesn't happen for arbitrary synthetic events
   dispatched by author script. However, the <code title=dom-click><a
   href="#click">click()</a></code> method can be used to make it happen
   programmatically.

  <p>For certain form controls, this process is complicated further by <a
   href="http://www.whatwg.org/specs/web-forms/current-work/#the-click">changes
   that must happen around the click event</a>. <a href="#refsWF2">[WF2]</a></p>
  <!-- XXX WF2: when this is merged into
  this spec, update xrefs -->

  <p class=note>Most interactive elements have content models that disallow
   nesting interactive elements.</p>
  <!--
   <li><span>Form control elements</span></li> XXX
-->

  <h5 id=paragraphs><span class=secno>3.3.3.6. </span>Paragraphs</h5>

  <p>A <dfn id=paragraph>paragraph</dfn> is typically a block of text with
   one or more sentences that discuss a particular topic, as in typography,
   but can also be used for more general thematic grouping. For instance, an
   address is also a paragraph, as is a part of a form, a byline, or a stanza
   in a poem.

  <p>Paragraphs can be represented by several elements. The <code><a
   href="#address">address</a></code> element always represents a paragraph
   of contact information for its section, the <code><a
   href="#aside">aside</a></code>, <code><a href="#nav">nav</a></code>,
   <code><a href="#footer">footer</a></code>, <code><a
   href="#li">li</a></code>, and <code><a href="#dd">dd</a></code> elements
   represent paragraphs with various specific semantics when they are <a
   href="#determining0" title="Determining if a particular element contains
   block-level elements or inline-level content">used as inline-level content
   containers</a>, the <code><a href="#figure">figure</a></code> element
   represents a paragraph in the form of <a href="#embedded0">embedded
   content</a>, and the <code><a href="#p">p</a></code> element represents
   all the other kinds of paragraphs, for which there are no dedicated
   elements.

  <h3 id=global><span class=secno>3.4. </span>Global attributes</h3>

  <p>The following attributes are common to and may be specified on all <a
   href="#html-elements">HTML elements</a> (even those not defined in this
   specification):

  <dl class=element>
   <dt>Global attributes:

   <dd><code title=attr-class><a href="#class">class</a></code>

   <dd><code title=attr-contenteditable><a
    href="#contenteditable0">contenteditable</a></code>

   <dd><code title=attr-contextmenu><a
    href="#contextmenu">contextmenu</a></code>

   <dd><code title=attr-dir><a href="#dir">dir</a></code>

   <dd><code title=attr-draggable><a href="#draggable">draggable</a></code>

   <dd><code title=attr-id><a href="#id">id</a></code>

   <dd><code title=attr-irrelevant><a
    href="#irrelevant">irrelevant</a></code>

   <dd><code title=attr-lang><a href="#lang">lang</a></code>

   <dd><code title=attr-tabindex><a href="#tabindex">tabindex</a></code>

   <dd><code title=attr-title><a href="#title">title</a></code>
  </dl>

  <p>In addition, the following <a href="#event2">event handler content
   attributes</a> may be specified on any <span>HTML element</span>:

  <ul class=brief>
   <li><code title=handler-onabort><a href="#onabort">onabort</a></code>

   <li><code title=handler-onbeforeunload><a
    href="#onbeforeunload">onbeforeunload</a></code>

   <li><code title=handler-onblur><a href="#onblur">onblur</a></code>

   <li><code title=handler-onchange><a href="#onchange">onchange</a></code>

   <li><code title=handler-onclick><a href="#onclick">onclick</a></code>

   <li><code title=handler-oncontextmenu><a
    href="#oncontextmenu">oncontextmenu</a></code>

   <li><code title=handler-ondblclick><a
    href="#ondblclick">ondblclick</a></code>

   <li><code title=handler-ondrag><a href="#ondrag">ondrag</a></code>

   <li><code title=handler-ondragend><a
    href="#ondragend">ondragend</a></code>

   <li><code title=handler-ondragenter><a
    href="#ondragenter">ondragenter</a></code>

   <li><code title=handler-ondragleave><a
    href="#ondragleave">ondragleave</a></code>

   <li><code title=handler-ondragover><a
    href="#ondragover">ondragover</a></code>

   <li><code title=handler-ondragstart><a
    href="#ondragstart">ondragstart</a></code>

   <li><code title=handler-ondrop><a href="#ondrop">ondrop</a></code>

   <li><code title=handler-onerror><a href="#onerror">onerror</a></code>

   <li><code title=handler-onfocus><a href="#onfocus">onfocus</a></code>

   <li><code title=handler-onkeydown><a
    href="#onkeydown">onkeydown</a></code>

   <li><code title=handler-onkeypress><a
    href="#onkeypress">onkeypress</a></code>

   <li><code title=handler-onkeyup><a href="#onkeyup">onkeyup</a></code>

   <li><code title=handler-onload><a href="#onload">onload</a></code>

   <li><code title=handler-onmessage><a
    href="#onmessage">onmessage</a></code>

   <li><code title=handler-onmousedown><a
    href="#onmousedown">onmousedown</a></code>

   <li><code title=handler-onmousemove><a
    href="#onmousemove">onmousemove</a></code>

   <li><code title=handler-onmouseout><a
    href="#onmouseout">onmouseout</a></code>

   <li><code title=handler-onmouseover><a
    href="#onmouseover">onmouseover</a></code>

   <li><code title=handler-onmouseup><a
    href="#onmouseup">onmouseup</a></code>

   <li><code title=handler-onmousewheel><a
    href="#onmousewheel">onmousewheel</a></code>

   <li><code title=handler-onresize><a href="#onresize">onresize</a></code>

   <li><code title=handler-onscroll><a href="#onscroll">onscroll</a></code>

   <li><code title=handler-onselect><a href="#onselect">onselect</a></code>

   <li><code title=handler-onsubmit><a href="#onsubmit">onsubmit</a></code>

   <li><code title=handler-onunload><a href="#onunload">onunload</a></code>
  </ul>

  <h4 id=the-id><span class=secno>3.4.1. </span>The <dfn id=id
   title=attr-id><code>id</code></dfn> attribute</h4>

  <p>The <code title=attr-id><a href="#id">id</a></code> attribute represents
   its element's unique identifier. The value must be unique in the subtree
   within which the element finds itself and must contain at least one
   character. The value must not contain any <a href="#space" title="space
   character">space characters</a>.</p>
  <!-- space characters are disallowed because space-separated lists
  of IDs otherwise would not be able to reach all valid IDs -->

  <p>If the value is not the empty string, user agents must associate the
   element with the given value (exactly, including any space characters) for
   the purposes of ID matching within the subtree the element finds itself
   (e.g. for selectors in CSS or for the <code>getElementById()</code> method
   in the DOM).

  <p>Identifiers are opaque strings. Particular meanings should not be
   derived from the value of the <code title=attr-id><a
   href="#id">id</a></code> attribute.

  <p>This specification doesn't preclude an element having multiple IDs, if
   other mechanisms (e.g. DOM Core methods) can set an element's ID in a way
   that doesn't conflict with the <code title=attr-id><a
   href="#id">id</a></code> attribute.

  <p>The <dfn id=id0 title=dom-id><code>id</code></dfn> DOM attribute must <a
   href="#reflect">reflect</a> the <code title=attr-id><a
   href="#id">id</a></code> content attribute.

  <h4 id=the-title><span class=secno>3.4.2. </span>The <dfn id=title
   title=attr-title><code>title</code></dfn> attribute</h4>

  <p>The <code title=attr-title><a href="#title">title</a></code> attribute
   represents advisory information for the element, such as would be
   appropriate for a tooltip. On a link, this could be the title or a
   description of the target resource; on an image, it could be the image
   credit or a description of the image; on a paragraph, it could be a
   footnote or commentary on the text; on a citation, it could be further
   information about the source; and so forth. The value is text.

  <p>If this attribute is omitted from an element, then it implies that the
   <code title=attr-title><a href="#title">title</a></code> attribute of the
   nearest ancestor with a <code title=attr-title><a
   href="#title">title</a></code> attribute set is also relevant to this
   element. Setting the attribute overrides this, explicitly stating that the
   advisory information of any ancestors is not relevant to this element.
   Setting the attribute to the empty string indicates that the element has
   no advisory information.

  <p>If the <code title=attr-title><a href="#title">title</a></code>
   attribute's value contains U+000A LINE FEED (LF) characters, the content
   is split into multiple lines. Each U+000A LINE FEED (LF) character
   represents a line break.

  <p>Some elements, such as <code><a href="#link">link</a></code> and
   <code><a href="#dfn">dfn</a></code>, define additional semantics for the
   <code title=attr-title><a href="#title">title</a></code> attribute beyond
   the semantics described above.

  <p>The <dfn id=title0 title=dom-title><code>title</code></dfn> DOM
   attribute must <a href="#reflect">reflect</a> the <code
   title=attr-title><a href="#title">title</a></code> content attribute.

  <h4 id=the-lang><span class=secno>3.4.3. </span>The <dfn id=lang
   title=attr-lang><code>lang</code></dfn> (HTML only) and <dfn id=xmllang
   title=attr-xml-lang><code>xml:lang</code></dfn> (XML only) attributes</h4>

  <p>The <code title=attr-lang><a href="#lang">lang</a></code> attribute
   specifies the primary <dfn id=language>language</dfn> for the element's
   contents and for any of the element's attributes that contain text. Its
   value must be a valid RFC 3066 language code, or the empty string. <a
   href="#refsRFC3066">[RFC3066]</a>

  <p>The <code title=attr-xml-lang><a href="#xmllang">xml:lang</a></code>
   attribute is defined in XML. <a href="#refsXML">[XML]</a>

  <p>If these attributes are omitted from an element, then it implies that
   the language of this element is the same as the language of the parent
   element. Setting the attribute to the empty string indicates that the
   primary language is unknown.

  <p>The <code title=attr-lang><a href="#lang">lang</a></code> attribute may
   only be used on elements of <a href="#html-">HTML documents</a>. Authors
   must not use the <code title=attr-lang><a href="#lang">lang</a></code>
   attribute in <a href="#xml-documents">XML documents</a>.

  <p>The <code title=attr-xml-lang><a href="#xmllang">xml:lang</a></code>
   attribute may only be used on elements of <a href="#xml-documents">XML
   documents</a>. Authors must not use the <code title=attr-xml-lang><a
   href="#xmllang">xml:lang</a></code> attribute in <a href="#html-">HTML
   documents</a>.</p>
  <!-- technically this
  is redundant with the XML spec -->

  <p>To determine the language of a node, user agents must look at the
   nearest ancestor element (including the element itself if the node is an
   element) that has a <code title=attr-lang><a href="#lang">lang</a></code>
   or <code title=attr-xml-lang><a href="#xmllang">xml:lang</a></code>
   attribute set. That specifies the language of the node.

  <p>If both the <code title=attr-xml-lang><a
   href="#xmllang">xml:lang</a></code> attribute and the <code
   title=attr-lang><a href="#lang">lang</a></code> attribute are set on an
   element, user agents must use the <code title=attr-xml-lang><a
   href="#xmllang">xml:lang</a></code> attribute, and the <code
   title=attr-lang><a href="#lang">lang</a></code> attribute must be <a
   href="#ignored" title=ignore>ignored</a> for the purposes of determining
   the element's language.

  <p>If no explicit language is given for the <a href="#root-element">root
   element</a>, then language information from a higher-level protocol (such
   as HTTP), if any, must be used as the final fallback language. In the
   absence of any language information, the default value is unknown (the
   empty string).

  <p>User agents may use the element's language to determine proper
   processing or rendering (e.g. in the selection of appropriate fonts or
   pronounciations, or for dictionary selection). <!--User
  agents must not use the element's language to determine text
  directionality. (commented out because text directionality is a
  rendering-level concern.)-->

  <p>The <dfn id=lang0 title=dom-lang><code>lang</code></dfn> DOM attribute
   must <a href="#reflect">reflect</a> the <code title=attr-lang><a
   href="#lang">lang</a></code> content attribute.

  <h4 id=the-dir><span class=secno>3.4.4. </span>The <dfn id=dir
   title=attr-dir><code>dir</code></dfn> attribute</h4>

  <p>The <code title=attr-dir><a href="#dir">dir</a></code> attribute
   specifies the element's text directionality. The attribute is an <a
   href="#enumerated">enumerated attribute</a> with the keyword <code
   title="">ltr</code> mapping to the state <em>ltr</em>, and the keyword
   <code title="">rtl</code> mapping to the state <em>rtl</em>. The attribute
   has no defaults.

  <p>If the attribute has the state <em>ltr</em>, the element's
   directionality is left-to-right. If the attribute has the state
   <em>rtl</em>, the element's directionality is right-to-left. Otherwise,
   the element's directionality is the same as its parent.

  <p>The processing of this attribute depends on the presentation layer. For
   example, CSS 2.1 defines a mapping from this attribute to the CSS
   'direction' and 'unicode-bidi' properties, and defines rendering in terms
   of those properties.

  <p>The <dfn id=dir0 title=dom-dir><code>dir</code></dfn> DOM attribute on
   an element must <a href="#reflect">reflect</a> the <code title=attr-dir><a
   href="#dir">dir</a></code> content attribute of that element, <a
   href="#limited">limited to only known values</a>.

  <p>The <dfn id=dir1 title=dom-document-dir><code>dir</code></dfn> DOM
   attribute on <code><a href="#htmldocument">HTMLDocument</a></code> objects
   must <a href="#reflect">reflect</a> the <code title=attr-dir><a
   href="#dir">dir</a></code> content attribute of <a href="#the-html0">the
   <code>html</code> element</a>, if any, <a href="#limited">limited to only
   known values</a>. If there is no such element, then the attribute must
   return the empty string and do nothing on setting.

  <h4 id=classes><span class=secno>3.4.5. </span>The <dfn id=class
   title=attr-class><code>class</code></dfn> attribute</h4>

  <p>Every <span>HTML element</span> may have a <code title=attr-class><a
   href="#class">class</a></code> attribute specified.

  <p>The attribute, if specified, must have a value that is an <a
   href="#unordered">unordered set of space-separated tokens</a> representing
   the various classes that the element belongs to.

  <p>The classes that an HTML element has assigned to it consists of all the
   classes returned when the value of the <code title=attr-class><a
   href="#class">class</a></code> attribute is <a href="#split" title="split
   a string on spaces">split on spaces</a>.

  <p class=note>Assigning classes to an element affects class matching in
   selectors in CSS, the <code title=dom-document-getElementsByClassName><a
   href="#getelementsbyclassname">getElementsByClassName()</a></code> method
   in the DOM, and other such features.

  <p>Authors may use any value in the <code title=attr-class><a
   href="#class">class</a></code> attribute, but are encouraged to use the
   values that describe the nature of the content, rather than values that
   describe the desired presentation of the content.

  <p>The <dfn id=classname title=dom-className><code>className</code></dfn>
   and <dfn id=classlist title=dom-classList><code>classList</code></dfn> DOM
   attributes must both <a href="#reflect">reflect</a> the <code
   title=attr-class><a href="#class">class</a></code> content attribute.

  <h4 id=the-irrelevant><span class=secno>3.4.6. </span>The <dfn
   id=irrelevant title=attr-irrelevant><code>irrelevant</code></dfn>
   attribute</h4>

  <p>All elements may have the <code title=attr-irrelevant><a
   href="#irrelevant">irrelevant</a></code> content attribute set. The <code
   title=attr-irrelevant><a href="#irrelevant">irrelevant</a></code>
   attribute is a <a href="#boolean0">boolean attribute</a>. When specified
   on an element, it indicates that the element is not yet, or is no longer,
   relevant. User agents should not render elements that have the <code
   title=attr-irrelevant><a href="#irrelevant">irrelevant</a></code>
   attribute specified.

  <div class=example>
   <p>In the following skeletal example, the attribute is used to hide the a
    Web game until the user logs in:</p>

   <pre>  &lt;h1>The Example Game&lt;/h1>
  &lt;section id="login">
   &lt;h2>Login&lt;/h2>
   &lt;form>
    ...
    &lt;!-- calls login() once the user's credentials have been checked -->
   &lt;/form>
   &lt;script>
    function login() {
      // switch screens
      document.getElementById('login').irrelevant = true;
      document.getElementById('game').irrelevant = false;
    }
   &lt;/script>
  &lt;/section>
  &lt;section id="game">
   ...
  &lt;/section></pre>

   <p>In the following example, an image acts as a surrogate for an video.
    When the image is clicked, it tries to load the video (and disables the
    playback button). If the load succeeds enough that a frame of data has
    been downloaded, the <code><a href="#video1">video</a></code> element
    hides the surrogate image and shows the video instead, along with its
    controls, and turns on autoplay (so that the video will commence playback
    as soon as enough of it is loaded). If the load fails for any reason, the
    video and the surrogate frame are both hidden (by hiding the paragraph
    element containing them both), and the following paragraph is shown
    instead, with its unhelpful error message and potentially helpful link to
    download the video directly.</p>

   <p>In legacy user agents, the surrogate image would show (though clicking
    it would have no effect) and the link to the video would be present
    (allowing the video to be viewed in another application).</p>

   <pre>  &lt;p>
   &lt;input type="image" src="frame.png" alt="Play Video"
     onclick="   nextSibling.load();
                 disabled = true;
                 return false;"
   >&lt;video src="video.ogg" controls="" irrelevant=""
     onloadedfirstframe="
                 irrelevant = false;
                 previousSibling.irrelevant = true;
                 autoplay = true"
     onerror="   parentNode.irrelevant = true;
                 parentNode.nextSibling.irrelevant = false">
   &lt;/video>
  &lt;/p>&lt;p irrelevant="">
   Playback unavailable.
   &lt;a href="video.ogg">Download Video&lt;/a>
  &lt;/p></pre>
  </div>

  <p>The <code title=attr-irrelevant><a
   href="#irrelevant">irrelevant</a></code> attribute must not be used to
   hide content that could legitimately be shown in another presentation. For
   example, it is incorrect to use <code title=attr-irrelevant><a
   href="#irrelevant">irrelevant</a></code> to hide panels in a tabbed
   dialog, because the tabbed interface is merely a kind of overflow
   presentation &mdash; showing all the form controls in one big page with a
   scrollbar would be equivalent, and no less correct.

  <p>Elements in a section hidden by the <code title=attr-irrelevant><a
   href="#irrelevant">irrelevant</a></code> attribute are still active, e.g.
   scripts and form controls in such sections still render execute and submit
   respectively. Only their presentation to the user changes.

  <p>The <dfn id=irrelevant0
   title=dom-irrelevant><code>irrelevant</code></dfn> DOM attribute must <a
   href="#reflect">reflect</a> the content attribute of the same name.

  <h3 id=interaction><span class=secno>3.5. </span><dfn
   id=interaction0>Interaction</dfn></h3>
  <!--
ELEMENT
           attribute long <span title="dom-tabindex">tabIndex</span>;
  void <span title="dom-click">click</span>();
  void <span title="dom-focus">focus</span>();
  void <span title="dom-blur">blur</span>();
  void <span title="dom-scrollIntoView">scrollIntoView</span>();
  void <span title="dom-scrollIntoView">scrollIntoView</span>(in boolean top);

DOCUMENT
  readonly attribute <span>Element</span> <span title="dom-document-activeElement">activeElement</span>;
  readonly attribute boolean <span title="dom-document-hasFocus">hasFocus</span>;
-->

  <h4 id=activation><span class=secno>3.5.1. </span>Activation</h4>

  <p>The <dfn id=click title=dom-click>click()</dfn> method must <a
   href="#firing">fire a <code>click</code> event</a> at the element, whose
   default action is the <span title="fire a DOMActivate event">firing of a
   further <code title=event-DOMActivate>DOMActivate</code> event</span> at
   the same element, whose own default action is to go through all the
   elements the <code title=event-DOMActivate>DOMActivate</code> event
   bubbled through (starting at the target node and going towards the
   <code>Document</code> node), looking for an element with an <a
   href="#activation0">activation behavior</a>; the first element, in reverse
   tree order, to have one, must have its activation behavior executed.

  <h4 id=focus><span class=secno>3.5.2. </span>Focus</h4>

  <p>When an element is <em>focused</em>, key events received by the document
   must be targeted at that element. There is always an element focused; in
   the absence of other elements being focused, the document's root element
   is it.

  <p>Which element within a document currently has focus is independent of
   whether or not the document itself has the <em>system focus</em>.

  <p>Some focusable elements might take part in <em>sequential focus
   navigation</em>.

  <h5 id=focus-management><span class=secno>3.5.2.1. </span>Focus management</h5>

  <p>The <dfn id=focus0 title=dom-focus><code>focus()</code></dfn> and <dfn
   id=blur title=dom-blur><code>blur()</code></dfn> methods must focus and
   unfocus the element respectively, if the element is focusable.

  <p>Some elements, most notably <code><a href="#area">area</a></code>, can
   correspond to more than one distinct focusable area. When such an element
   is focused using the <code title=dom-focus><a
   href="#focus0">focus()</a></code> method, the first such region in tree
   order is the one that must be focused.

  <p class=big-issue>Well that clearly needs more.</p>
  <!-- XXX e.g. should the click, focus, blur methods be recursible? -->

  <p>The <dfn id=activeelement
   title=dom-document-activeElement><code>activeElement</code></dfn>
   attribute must return the element in the document that has focus. If no
   element specifically has focus, this must return <a href="#the-body0">the
   <code>body</code> element</a>.

  <p>The <dfn id=hasfocus
   title=dom-document-hasFocus><code>hasFocus</code></dfn> attribute must
   return true if the document, one of its nested <a href="#browsing0"
   title="browsing context">browsing contexts</a>, or any element in the
   document or its browsing contexts currently has the system focus.

  <h5 id=sequential><span class=secno>3.5.2.2. </span>Sequential focus
   navigation</h5>

  <p class=issue>This section on the <code>tabindex</code> attribute needs to
   be checked for backwards-compatibility.

  <p>The <dfn id=tabindex title=attr-tabindex><code>tabindex</code></dfn>
   attribute specifies the relative order of elements for the purposes of
   sequential focus navigation. The name "tab index" comes from the common
   use of the "tab" key to navigate through the focusable elements. The term
   "tabbing" refers to moving forward through the focusable elements.

  <p>The <code title=attr-tabindex><a href="#tabindex">tabindex</a></code>
   attribute, if specified, must have a value that is a <a
   href="#valid0">valid integer</a>.

  <p>If the attribute is specified, it must be parsed using the <a
   href="#rules0">rules for parsing integers</a>. If parsing the value
   returns an error, the attribute is ignored for the purposes of focus
   management (as if it wasn't specified).

  <p>A positive integer or zero specifies the index of the element in the
   current scope's tab order. Elements with the same index are sorted in <a
   href="#tree-order">tree order</a> for the purposes of tabbing.

  <p id=negative-tabindex>A negative integer specifies that the element
   should be removed from the tab order. If the element does normally take
   focus, it may still be focused using other means (e.g. it could be focused
   by a click).

  <p>If the attribute is absent (or invalid), then the user agent must treat
   the element as if it had the value 0 or the value -1, based on platform
   conventions.

  <p class=example>For example, a user agent might default
   <code>textarea</code> elements to 0, and <code>button</code> elements to
   -1, making text fields part of the tabbing cycle but buttons not.

  <p>When an element that does not normally take focus (i.e. whose default
   value would be -1) has the <code title=attr-tabindex><a
   href="#tabindex">tabindex</a></code> attribute specified with a positive
   value, then it should be added to the tab order and should be made
   focusable. When focused, the element matches the CSS <code>:focus</code>
   pseudo-class and key events are dispatched on that element in response to
   keyboard input.

  <p>The <dfn id=tabindex0 title=dom-tabIndex><code>tabIndex</code></dfn> DOM
   attribute reflects the value of the <code title=attr-tabIndex><a
   href="#tabindex">tabIndex</a></code> content attribute. If the attribute
   is not present (or has an invalid value) then the DOM attribute must
   return the UA's default value for that element, which will be either 0
   (for elements in the tab order) or -1 (for elements not in the tab order).</p>
  <!--XXX
  <h5>The <dfn><code>DocumentFocus</code></dfn> interface</h5>

  <p>The <code>DocumentFocus</code> interface contains methods for
  moving focus around the document. It can be obtained from objects
  that implement the <code>Document</code> interface using
  binding-specific casting methods.</p>

  <pre class="idl">interface <dfn>DocumentFocus</dfn> {
  void moveFocusForward();
  void moveFocusBackward();
  void moveFocusUp();
  void moveFocusRight();
  void moveFocusDown();
  void moveFocusLeft();
};</pre>

  <p>The <dfn><code>currentFocus</code></dfn> attribute returns the
  element to which key events will be sent when the document receives
  key events.</p>

  <p>The <dfn><code>moveFocusForward</code></dfn> method uses the
  <code>'nav-index'</code> property and the <code>tabindex</code>
  attribute to find the next focusable element and focuses it.</p>

  <p>The <dfn><code>moveFocusBackward</code></dfn> method uses the
  <code>'nav-index'</code> property and the <code>tabindex</code>
  attribute to find the previous focusable element and focuses
  it.</p>

  <p>The <dfn><code>moveFocusUp</code></dfn> method uses the
  <code>'nav-up'</code> property and the <code>tabindex</code>
  attribute to find an appropriate focusable element and focuses
  it.</p>

  <p>In a similar manner, the <dfn><code>moveFocusRight</code></dfn>,
  <dfn><code>moveFocusDown</code></dfn>, and
  <dfn><code>moveFocusLeft</code></dfn> methods use the
  <code>'nav-right'</code>, <code>'nav-down'</code>, and
  <code>'nav-left'</code> properties (respectively), and the
  <code>tabindex</code> attribute, to find an appropriate focusable
  element and focus it.</p>

  <p>The <code>'nav-index'</code>, <code>'nav-up'</code>,
  <code>'nav-right'</code>, <code>'nav-down'</code>, and
  <code>'nav-left'</code> properties are defined in <a
  href="#refsCSS3UI">[CSS3UI]</a>.</p>

Other things to look at are IE's focus APIs (document.activeElement,
document.hasFocus, HTMLElement.setActive(), onBeforeActivate,
onActivate, onBeforeDeactivate, onDeactivate, document.hasFocus):
   https://bugzilla.mozilla.org/show_bug.cgi?id=296471
   https://bugzilla.mozilla.org/show_bug.cgi?id=296469
   http://msdn.microsoft.com/workshop/author/dhtml/reference/properties/activeelement.asp
   http://msdn.microsoft.com/workshop/author/dhtml/reference/methods/setactive.asp
   http://msdn.microsoft.com/workshop/author/dhtml/reference/events/onbeforeactivate.asp
   http://msdn.microsoft.com/workshop/author/dhtml/reference/methods/focus.asp
-->

  <h4 id=scrolling><span class=secno>3.5.3. </span>Scrolling elements into
   view</h4>

  <p>The <dfn id=scrollintoview
   title=dom-scrollIntoView><code>scrollIntoView([<var
   title="">top</var>])</code></dfn> method, when called, must cause the
   element on which the method was called to have the attention of the user
   called to it.

  <p class=note>In a speech browser, this could happen by having the current
   playback position move to the start of the given element.

  <p>In visual user agents, if the argument is present and has the value
   false, the user agent should scroll the element into view such that both
   the bottom and the top of the element are in the viewport, with the bottom
   of the element aligned with the bottom of the viewport. If it isn't
   possible to show the entire element in that way, or if the argument is
   omitted or is true, then the user agent must instead simply align the top
   of the element with the top of the viewport.

  <p>Non-visual user agents may ignore the argument, or may treat it in some
   media-specific manner most useful to the user.</p>
  <!-- XXX maybe this should move to CSSOM -->

  <h3 id=the-root><span class=secno>3.6. </span>The root element</h3>

  <h4 id=the-html><span class=secno>3.6.1. </span>The <dfn
   id=html><code>html</code></dfn> element</h4>

  <dl class=element>
   <dt>Contexts in which this element may be used:

   <dd>As the root element of a document.

   <dd>Wherever a subdocument fragment is allowed in a compound document.

   <dt>Content model:

   <dd>A <code><a href="#head">head</a></code> element followed by a <code><a
    href="#body0">body</a></code> element.</dd>
   <!--XXX
Steven Pemberton was as always, a remarkable speaker, but his answer
to my question leaves me a very bad taste. Basically, I asked him why
XHTML2 preserves the useless head and body element. The answer was in
substance "because this is a compromise". Ah. So XHTML2 preserves two
useless elements that add potential dangers to the interpretation and
styling of documents because it's a compromise. Getting rid of head
would allow to attach directly the document's metadata to the root
element of the document, making much more sense than a head element.
Having a head element also preserves the ridiculous
engraved-in-the-marble "head contents are not rendered". Body is
dangerous because it's another box between the document and the
contents; you all have written a blog template with a <div
class="main"> or <div class="content">. Why do we also need a body?
 - http://www.glazman.org/weblog/dotclear/index.php?2005/05/27/1055-adam-2
-->

   <dt>Element-specific attributes:

   <dd>None (but see prose).

   <dt>DOM interface:

   <dd>No difference from <code><a
    href="#htmlelement">HTMLElement</a></code>.
  </dl>

  <p>The <code><a href="#html">html</a></code> element represents the root of
   an HTML document.

  <p>Though it has absolutely no effect and no meaning, the <code><a
   href="#html">html</a></code> element, in <a href="#html-">HTML
   documents</a>, may have an <code title="">xmlns</code> attribute
   specified, if, and only if, it has the exact value
   "<code>http://www.w3.org/1999/xhtml</code>". This does not apply to <a
   href="#xml-documents">XML documents</a>.

  <p class=note>In HTML, the <code title="">xmlns</code> attribute has
   absolutely no effect. It is basically a talisman. It is allowed merely to
   make migration to and from XHTML mildly easier. When parsed by an <a
   href="#html-0">HTML parser</a>, the attribute ends up in the null
   namespace, not the "<code>http://www.w3.org/2000/xmlns/</code>" namespace
   like namespace declaration attributes in XML do.

  <p class=note>In XML, an <code title="">xmlns</code> attribute is part of
   the namespace declaration mechanism, and an element cannot actually have
   an <code title="">xmlns</code> attribute in the null namespace specified.

  <h3 id=document><span class=secno>3.7. </span>Document metadata</h3>

  <p>Document metadata is represented by <dfn id=metadata>metadata
   elements</dfn> in the document's <code><a href="#head">head</a></code>
   element.

  <h4 id=the-head><span class=secno>3.7.1. </span>The <dfn
   id=head><code>head</code></dfn> element</h4>

  <dl class=element>
   <dt>Contexts in which this element may be used:

   <dd>As the first element in an <code><a href="#html">html</a></code>
    element.

   <dt>Content model:

   <dd>In any order unless otherwise specified: optionally one <code><a
    href="#meta0">meta</a></code> element with a <code
    title=attr-meta-charset><a href="#charset0">charset</a></code> attribute,
    exactly one <code><a href="#title1">title</a></code> element, optionally
    one <code><a href="#base">base</a></code> element, and zero or more other
    <a href="#metadata">metadata elements</a> (in particular, <code><a
    href="#link">link</a></code>, <code><a href="#meta0">meta</a></code>,
    <code><a href="#style">style</a></code>, and <code><a
    href="#script0">script</a></code>).

   <dt>Element-specific attributes:

   <dd>None.

   <dt>DOM interface:

   <dd>No difference from <code><a
    href="#htmlelement">HTMLElement</a></code>.
  </dl>

  <p>The <code><a href="#head">head</a></code> element collects the
   document's metadata.

  <h4 id=the-title0><span class=secno>3.7.2. </span>The <dfn
   id=title1><code>title</code></dfn> element</h4>

  <p><a href="#metadata" title="metadata elements">Metadata element</a>.

  <dl class=element>
   <dt>Contexts in which this element may be used:

   <dd>In a <code><a href="#head">head</a></code> element containing no other
    <code><a href="#title1">title</a></code> elements.

   <dt>Content model:

   <dd>Text (for details, see prose).

   <dt>Element-specific attributes:

   <dd>None.

   <dt>DOM interface:

   <dd>No difference from <code><a
    href="#htmlelement">HTMLElement</a></code>.
  </dl>

  <p>The <code><a href="#title1">title</a></code> element represents the
   document's title or name. Authors should use titles that identify their
   documents even when they are used out of context, for example in a user's
   history or bookmarks, or in search results. The document's title is often
   different from its first header, since the first header does not have to
   stand alone when taken out of context.

  <div class=example>
   <p>Here are some examples of appropriate titles, contrasted with the
    top-level headers that might be used on those same pages.</p>

   <pre>  &lt;title>Introduction to The Mating Rituals of Bees&lt;/title>
    ...
  &lt;h1>Introduction&lt;/h1>
  &lt;p>This companion guide to the highly successful
  &lt;cite>Introduction to Medieval Bee-Keeping&lt;/cite> book is...
</pre>

   <p>The next page might be a part of the same site. Note how the title
    describes the subject matter unambiguously, while the first header
    assumes the reader knowns what the context is and therefore won't wonder
    if the dances are Salsa or Waltz:</p>

   <pre>  &lt;title>Dances used during bee mating rituals&lt;/title>
    ...
  &lt;h1>The Dances&lt;/h1></pre>
  </div>

  <p>The <code><a href="#title1">title</a></code> element must not contain
   any elements.

  <p>The string to use as the document's title is given by the <code
   title=dom-document-title><a
   href="#document.title">document.title</a></code> DOM attribute. User
   agents should use the document's title when referring to the document in
   their user interface.

  <h4 id=the-base><span class=secno>3.7.3. </span>The <dfn
   id=base><code>base</code></dfn> element</h4>

  <p><a href="#metadata" title="metadata elements">Metadata element</a>.

  <dl class=element>
   <dt>Contexts in which this element may be used:

   <dd>In a <code><a href="#head">head</a></code> element, after the <code><a
    href="#meta0">meta</a></code> element with the <code
    title=attr-meta-charset><a href="#charset0">charset</a></code> attribute,
    if any, but before any other elements.

   <dt>Content model:

   <dd>Empty.

   <dt>Element-specific attributes:

   <dd><code title=attr-base-href><a href="#href">href</a></code>

   <dd><code title=attr-base-target><a href="#target">target</a></code>

   <dt>DOM interface:

   <dd>
    <pre
     class=idl>interface <dfn id=htmlbaseelement>HTMLBaseElement</dfn> : <a href="#htmlelement">HTMLElement</a> {
           attribute DOMString <a href="#href0" title=dom-base-href>href</a>;
           attribute DOMString <a href="#target0" title=dom-base-target>target</a>;
};</pre>
  </dl>

  <p>The <code><a href="#base">base</a></code> element allows authors to
   specify the document's base URI for the purposes of resolving relative
   URIs, and the name of the default <a href="#browsing0">browsing
   context</a> for the purposes of <a href="#following0">following
   hyperlinks</a>.

  <p>There must be no more than one <code><a href="#base">base</a></code>
   element per document.

  <p>The <dfn id=href title=attr-base-href><code>href</code></dfn> content
   attribute, if specified, must contain a URI (or IRI).

  <p>User agents must use the value of the <code
   title=att-base-href>href</code> attribute of the first <code><a
   href="#base">base</a></code> element that is both a child of <a
   href="#the-head0">the <code>head</code> element</a> and has an <code
   title=att-base-href>href</code> attribute, if there is such an element, as
   the document entity's base URI for the purposes of section 5.1.1 of RFC
   2396 ("Establishing a Base URI": "Base URI within Document Content"). This
   base URI from RFC 2396 is referred to by the algorithm given in XML Base,
   which <a href="#xmlBase">is a normative part of this specification</a>. <a
   href="#refsRFC2396">[RFC2396]</a>

  <p>If the base URI given by this attribute is a relative URI, it must be
   resolved relative to the higher-level base URIs (i.e. the base URI from
   the encapsulating entity or the URI used to retrieve the entity) to obtain
   an absolute base URI. All <code title=attr-xml-base>xml:base</code>
   attributes must be ignored when resolving relative URIs in this <code
   title=attr-base-href><a href="#href">href</a></code> attribute.

  <p class=note>If there are multiple <code><a href="#base">base</a></code>
   elements with <code title=att-base-href>href</code> attributes, all but
   the first are ignored.

  <p>The <dfn id=target title=attr-base-target><code>target</code></dfn>
   attribute, if specified, must contain a <a href="#valid8">valid browsing
   context name</a>. User agents use this name when <a
   href="#following0">following hyperlinks</a>.

  <p>The <dfn id=href0 title=dom-base-href><code>href</code></dfn> and <dfn
   id=target0 title=dom-base-target><code>target</code></dfn> DOM attributes
   must <a href="#reflect">reflect</a> the content attributes of the same
   name.

  <p class=note>Pages with multiple <code><a href="#base">base</a></code>
   elements have all but their first <code><a href="#base">base</a></code>
   element with an <code title=attr-base-href><a href="#href">href</a></code>
   attribute ignored for the purposes of URI resolution, and all but their
   first <code><a href="#base">base</a></code> element with a <code
   title=attr-base-target><a href="#target">target</a></code> attribute
   ignored for the purposes of default browsing context name resolution.</p>
  <!-- XXX the former is for compat with IE7. The latter is not
  actually exactly compatible with anything. We'll see if it breaks
  anything. -->

  <h4 id=the-link><span class=secno>3.7.4. </span>The <dfn
   id=link><code>link</code></dfn> element</h4>

  <p><a href="#metadata" title="metadata elements">Metadata element</a>.

  <dl class=element>
   <dt>Contexts in which this element may be used:

   <dd>In a <code><a href="#head">head</a></code> element.

   <dt>Content model:

   <dd>Empty.

   <dt>Element-specific attributes:

   <dd><code title=attr-link-href><a href="#href1">href</a></code> (required)

   <dd><code title=attr-link-rel><a href="#rel">rel</a></code> (required)

   <dd><code title=attr-link-media><a href="#media0">media</a></code>

   <dd><code title=attr-link-hreflang><a href="#hreflang">hreflang</a></code>

   <dd><code title=attr-link-type><a href="#type">type</a></code>

   <dd>Also, the <code title=attr-link-title><a
    href="#title2">title</a></code> attribute has special semantics on this
    element.

   <dt>DOM interface:

   <dd>
    <pre
     class=idl>interface <dfn id=htmllinkelement>HTMLLinkElement</dfn> : <a href="#htmlelement">HTMLElement</a> {
           attribute boolean <a href="#disabled" title=dom-link-disabled>disabled</a>;
           attribute DOMString <a href="#href2" title=dom-link-href>href</a>;
           attribute DOMString <a href="#rel0" title=dom-link-rel>rel</a>;
  readonly attribute DOMTokenList <a href="#rellist" title=dom-link-relList>relList</a>;
           attribute DOMString <a href="#media1" title=dom-link-media>media</a>;
           attribute DOMString <a href="#hreflang0" title=dom-link-hreflang>hreflang</a>;
           attribute DOMString <a href="#type0" title=dom-link-type>type</a>;
};</pre>

    <p>The <code>LinkStyle</code> interface must also be implemented by this
     element, the <a href="#styling0">styling processing model</a> defines
     how. <a href="#refsCSSOM">[CSSOM]</a></p>
  </dl>

  <p>The <code><a href="#link">link</a></code> element allows authors to
   indicate explicit relationships between their document and other
   resources.

  <p>The destination of the link is given by the <dfn id=href1
   title=attr-link-href><code>href</code></dfn> attribute, which must be
   present and must contain a URI (or IRI). If the <code
   title=attr-link-href><a href="#href1">href</a></code> attribute is absent,
   then the element does not define a link.

  <p>The type of link indicated (the relationship) is given by the value of
   the <dfn id=rel title=attr-link-rel><code>rel</code></dfn> attribute,
   which must be present, and must have a value that is an <a
   href="#unordered">unordered set of space-separated tokens</a>. The <a
   href="#linkTypes">allowed values and their meanings</a> are defined in a
   later section. If the <code title=attr-link-rel><a
   href="#rel">rel</a></code> attribute is absent, or if the value used is
   not allowed according to the definitions in this specification, then the
   element does not define a link.

  <p>Two categories of links can be created using the <code><a
   href="#link">link</a></code> element. <dfn id=links1 title="external
   resource link">Links to external resources</dfn> are links to resources
   that are to be used to augment the current document, and <dfn
   id=hyperlink1 title="hyperlink link">hyperlink links</dfn> are <a
   href="#hyperlinks" title=hyperlink>links to other documents</a>. The <a
   href="#linkTypes">link types section</a> defines whether a particular link
   type is an external resource or a hyperlink. One element can create
   multiple links (of which some might be external resource links and some
   might be hyperlinks). User agents should process the links on a per-link
   basis, not a per-element basis.

  <p>The exact behaviour for links to external resources depends on the exact
   relationship, as defined for the relevant link type. Some of the
   attributes control whether or not the external resource is to be applied
   (as defined below). For external resources that are represented in the DOM
   (for example, style sheets), the DOM representation must be made available
   even if the resource is not applied. (However, user agents may opt to only
   fetch such resources when they are needed, instead of pro-actively
   downloading all the external resources that are not applied.)

  <p>Interactive user agents should provide users with a means to <a
   href="#following0" title="following hyperlinks">follow the hyperlinks</a>
   created using the <code><a href="#link">link</a></code> element, somewhere
   within their user interface. The exact interface is not defined by this
   specification, but it should include the following information (obtained
   from the element's attributes, again as defined below), in some form or
   another (possibly simplified), for each hyperlink created with each
   <code><a href="#link">link</a></code> element in the document:

  <ul><!-- the order here is the order that makes most sense for a UI -->

   <li>The relationship between this document and the resource (given by the
    <code title=attr-link-rel><a href="#rel">rel</a></code> attribute)

   <li>The title of the resource (given by the <code title=attr-link-title><a
    href="#title2">title</a></code> attribute).

   <li>The URI of the resource (given by the <code title=attr-link-href><a
    href="#href1">href</a></code> attribute).

   <li>The language of the resource (given by the <code
    title=attr-link-hreflang><a href="#hreflang">hreflang</a></code>
    attribute).

   <li>The optimum media for the resource (given by the <code
    title=attr-link-media><a href="#media0">media</a></code> attribute).
  </ul>

  <p>User agents may also include other information, such as the type of the
   resource (as given by the <code title=attr-link-type><a
   href="#type">type</a></code> attribute).

  <p>The <dfn id=media0 title=attr-link-media><code>media</code></dfn>
   attribute says which media the resource applies to. The value must be a
   valid media query. <a href="#refsMQ">[MQ]</a>

  <p>If the link is a <a href="#hyperlink1" title="hyperlink
   link">hyperlink</a> then the <code title=attr-link-media><a
   href="#media0">media</a></code> attribute is purely advisory, and
   describes for which media the document in question was designed.

  <p>However, if the link is an <a href="#links1">external resource link</a>,
   then the <code title=attr-link-media><a href="#media0">media</a></code>
   attribute is prescriptive. The user agent must only apply the external
   resource to <span>views</span><!-- XXX xref --> while their state match
   the listed media.

  <p id=default-media>The default, if the <code title=attr-link-media><a
   href="#media0">media</a></code> attribute is omitted, is <code>all</code>,
   meaning that by default links apply to all media.

  <p>The <dfn id=hreflang
   title=attr-link-hreflang><code>hreflang</code></dfn> attribute on the
   <code><a href="#link">link</a></code> element has the same semantics as
   the <a href="#hreflang3"
   title=attr-hyperlink-hreflang><code>hreflang</code> attribute on hyperlink
   elements</a>.

  <p>The <dfn id=type title=attr-link-type><code>type</code></dfn> attribute
   gives the MIME type of the linked resource. It is purely advisory. The
   value must be a valid MIME type, optionally with parameters. <a
   href="#refsRFC2046">[RFC2046]</a>

  <p>For <a href="#links1" title="external resource link">external resource
   links</a>, user agents may use the type given in this attribute to decide
   whether or not to consider using the resource at all. If the UA does not
   support the given MIME type for the given link relationship, then the UA
   may opt not to download and apply the resource.

  <p>User agents must not consider the <code title=attr-link-type><a
   href="#type">type</a></code> attribute authoritative &mdash; upon fetching
   the resource, user agents must not use metadata included in the link to
   the resource to determine its type.

  <p>If the attribute is omitted, then the UA must fetch the resource to
   determine its type and thus determine if it supports (and can apply) that
   external resource.

  <div class=example>
   <p>If a document contains three style sheet links labelled as follows:</p>

   <pre>&lt;link rel="stylesheet" href="A" type="text/css"&gt;
&lt;link rel="stylesheet" href="B" type="text/plain"&gt;
&lt;link rel="stylesheet" href="C"&gt;</pre>

   <p>...then a compliant UA that supported only CSS style sheets would fetch
    the A and C files, and skip the B file (since <code>text/plain</code> is
    not the MIME type for CSS style sheets). For these two files, it would
    then check the actual types returned by the UA. For those that are sent
    as <code>text/css</code>, it would apply the styles, but for those
    labelled as <code>text/plain</code>, or any other type, it would not.</p>
  </div>
  <!--(to be deleted) (charset dropped)
  <p>The <dfn title="attr-link-charset"><code>charset</code></dfn>
  attribute gives the character encoding of the linked resource. It is
  purely advisory. The value must be a valid character encoding name.
  <a href="#refsIANACHARSET">[IANACHARSET]</a></p>

  <p>For <span title="external resource link">external resource
  links</span>, user agents may use the character encoding given in
  this attribute to decide whether or not to consider using the
  resource at all. If the UA does not support the given encoding for
  the given link relationship, then the UA may opt not to download and
  apply the resource.</p>

  <p>However, once the resource has been fetched, user agents must
  follow the rules for that resource type when determining the actual
  character encoding.</p>
-->

  <p>The <dfn id=title2 title=attr-link-title><code>title</code></dfn>
   attribute gives the title of the link. With one exception, it is purely
   advisory. The value is text. The exception is for style sheet links, where
   the <code title=attr-link-title><a href="#title2">title</a></code>
   attribute defines <a href="#alternative">alternative style sheet sets</a>.

  <p class=note>The <code title=attr-link-title><a
   href="#title2">title</a></code> attribute on <code><a
   href="#link">link</a></code> elements differs from the global <code
   title=attr-title><a href="#title">title</a></code> attribute of most other
   elements in that a link without a title does not inherit the title of the
   parent element: it merely has no title.

  <p>Some versions of HTTP defined a <code title="">Link:</code> header, to
   be processed like a series of <code><a href="#link">link</a></code>
   elements. When processing links, those must be taken into consideration as
   well. For the purposes of ordering, links defined by HTTP headers must be
   assumed to come before any links in the document, in the order that they
   were given in the HTTP entity header. Relative URIs in these headers must
   be resolved according to the rules given in HTTP, not relative to base
   URIs set by the document (e.g. using a <code><a
   href="#base">base</a></code> element or <code
   title=attr-xml-base>xml:base</code> attributes). <a
   href="#refsRFC2616">[RFC2616]</a> <a href="#refsRFC2068">[RFC2068]</a>

  <p>The DOM attributes <dfn id=href2
   title=dom-link-href><code>href</code></dfn>, <dfn id=rel0
   title=dom-link-rel><code>rel</code></dfn>, <dfn id=media1
   title=dom-link-media><code>media</code></dfn>, <dfn id=hreflang0
   title=dom-link-hreflang><code>hreflang</code></dfn>, and <dfn id=type0
   title=dom-link-type><code>type</code></dfn> each must <a
   href="#reflect">reflect</a> the respective content attributes of the same
   name.

  <p>The DOM attribute <dfn id=rellist
   title=dom-link-rellist><code>relList</code></dfn> must <a
   href="#reflect">reflect</a> the <code title=attr-link-rel><a
   href="#rel">rel</a></code> content attribute.

  <p>The DOM attribute <dfn id=disabled
   title=dom-link-disabled><code>disabled</code></dfn> only applies to style
   sheet links. When the <code><a href="#link">link</a></code> element
   defines a style sheet link, then the <code title=dom-link-disabled><a
   href="#disabled">disabled</a></code> attribute behaves as defined <a
   href="#disabled1" title=dom-linkstyle-disabled>for the alternative style
   sheets DOM</a>. For all other <code><a href="#link">link</a></code>
   elements it always return false and does nothing on setting.

  <h4 id=meta><span class=secno>3.7.5. </span>The <dfn
   id=meta0><code>meta</code></dfn> element</h4>

  <p><a href="#metadata" title="metadata elements">Metadata element</a>.

  <dl class=element>
   <dt>Contexts in which this element may be used:

   <dd>In a <code><a href="#head">head</a></code> element.

   <dt>Content model:

   <dd>Empty.

   <dt>Element-specific attributes:

   <dd><code title=attr-meta-name><a href="#name">name</a></code>

   <dd><code title=attr-meta-http-equiv><a
    href="#http-equiv0">http-equiv</a></code>

   <dd><code title=attr-meta-content><a href="#content0">content</a></code>

   <dd><code title=attr-meta-charset><a href="#charset0">charset</a></code>
    (<a href="#html-" title="HTML documents">HTML</a> only)

   <dt>DOM interface:

   <dd>
    <pre
     class=idl>interface <dfn id=htmlmetaelement>HTMLMetaElement</dfn> : <a href="#htmlelement">HTMLElement</a> {
           attribute DOMString <a href="#content1" title=dom-meta-content>content</a>;
           attribute DOMString <a href="#name0" title=dom-meta-name>name</a>;
           attribute DOMString <a href="#httpequiv" title=dom-meta-httpEquiv>httpEquiv</a>;
};</pre>
  </dl>

  <p>The <code><a href="#meta0">meta</a></code> element represents various
   kinds of metadata that cannot be expressed using the <code><a
   href="#title1">title</a></code>, <code><a href="#base">base</a></code>,
   <code><a href="#link">link</a></code>, <code><a
   href="#style">style</a></code>, and <code><a
   href="#script0">script</a></code> elements.

  <p>The <code><a href="#meta0">meta</a></code> element can represent
   document-level metadata with the <code title=attr-meta-name><a
   href="#name">name</a></code> attribute, pragma directives with the <code
   title=attr-meta-http-equiv><a href="#http-equiv0">http-equiv</a></code>
   attribute, and the file's character encoding declaration when an HTML
   document is serialised to string form (e.g. for transmission over the
   network or for disk storage) with the <code title=attr-meta-charset><a
   href="#charset0">charset</a></code> attribute.

  <p>Exactly one of the <code title=attr-meta-name><a
   href="#name">name</a></code>, <code title=attr-meta-http-equiv><a
   href="#http-equiv0">http-equiv</a></code>, and <code
   title=attr-meta-charset><a href="#charset0">charset</a></code> attributes
   must be specified.

  <p>If either <code title=attr-meta-name><a href="#name">name</a></code> or
   <code title=attr-meta-http-equiv><a
   href="#http-equiv0">http-equiv</a></code> is specified, then the <code
   title=attr-meta-content><a href="#content0">content</a></code> attribute
   must also be specified. Otherwise, it must be omitted.

  <p>The <code title=attr-meta-charset><a href="#charset0">charset</a></code>
   attribute may only be specified in <a href="#html5" title=HTML5>HTML
   documents</a>, it must not be used in <a href="#xhtml5" title=XHTML>XML
   documents</a>. If the <code title=attr-meta-charset><a
   href="#charset0">charset</a></code> attribute is specified, the element
   must be the first element in <a href="#the-head0">the <code>head</code>
   element</a> of the file.

  <p>The <dfn id=content0 title=attr-meta-content><code>content</code></dfn>
   attribute gives the value of the document metadata or pragma directive
   when the element is used for those purposes. The allowed values depend on
   the exact context, as described in subsequent sections of this
   specification.

  <p>If a <code><a href="#meta0">meta</a></code> element has a <dfn id=name
   title=attr-meta-name><code>name</code></dfn> attribute, it sets document
   metadata. Document metadata is expressed in terms of name/value pairs, the
   <code title=attr-meta-name><a href="#name">name</a></code> attribute on
   the <code><a href="#meta0">meta</a></code> element giving the name, and
   the <code title=attr-meta-content><a href="#content0">content</a></code>
   attribute on the same element giving the value. The name specifies what
   aspect of metadata is being set; valid names and the meaning of their
   values are described in the following sections. If a <code><a
   href="#meta0">meta</a></code> element has no <code
   title=attr-meta-content><a href="#content0">content</a></code> attribute,
   then the value part of the metadata name/value pair is the empty string.

  <p>The DOM attributes <dfn id=name0
   title=dom-meta-name><code>name</code></dfn> and <dfn id=content1
   title=dom-meta-content><code>content</code></dfn> must <a
   href="#reflect">reflect</a> the respective content attributes of the same
   name. The DOM attribute <dfn id=httpequiv
   title=dom-meta-httpEquiv><code>httpEquiv</code></dfn> must reflect the
   content attribute <code title=attr-meta-http-equiv><a
   href="#http-equiv0">http-equiv</a></code>.

  <h5 id=standard><span class=secno>3.7.5.1. </span>Standard metadata names</h5>

  <p>This specification defines a few names for the <code
   title=attr-meta-name><a href="#name">name</a></code> attribute of the
   <code><a href="#meta0">meta</a></code> element.

  <dl>
   <dt><dfn id=generator title=meta-generator>generator</dfn>

   <dd>
    <p>The value must be a free-form string that identifies the software used
     to generate the document. This value must not be used on hand-authored
     pages. WYSIWYG editors have <a href="#wysiwyg2" title="WYSIWYG
     signature">additional constraints</a> on the value used with this
     metadata name.

   <dt><dfn id=dns title=meta-dns>dns</dfn>

   <dd>
    <p>The value must be an <a href="#ordered">ordered set of unique
     space-separated tokens</a>, each word of which is a host name. The list
     allows authors to provide a list of host names that the user is expected
     to subsequently need. User agents may, according to user preferences and
     prevailing network conditions, pre-emptively resolve the given DNS names
     (extracting the names from the value using the <a href="#split"
     title="split a string on spaces">rules for splitting a string on
     spaces</a>), thus precaching the DNS information for those hosts and
     potentially reducing the time between page loads for subsequent user
     interactions. Higher priority should be given to host names given
     earlier in the list.
  </dl>

  <h5 id=other><span class=secno>3.7.5.2. </span>Other metadata names</h5>

  <p><dfn id=extensions title=concept-meta-extensions>Extensions to the
   predefined set of metadata names</dfn> may be registered in the <a
   href="http://wiki.whatwg.org/wiki/MetaExtensions">WHATWG Wiki
   MetaExtensions page</a>.

  <p>Anyone is free to edit the WHATWG Wiki MetaExtensions page at any time
   to add a type. These new names must be specified with the following
   information:

  <dl>
   <dt>Keyword

   <dd>
    <p>The actual name being defined. The name should not be confusingly
     similar to any other defined name (e.g. differing only in case).

   <dt>Brief description

   <dd>
    <p>A short description of what the metadata name's meaning is, including
     the format the value is required to be in.

   <dt>Link to more details

   <dd>A link to a more detailed description of the metadata name's semantics
    and requirements. It could be another page on the Wiki, or a link to an
    external page.

   <dt>Synonyms

   <dd>
    <p>A list of other names that have exactly the same processing
     requirements. Authors should not use the names defined to be synonyms,
     they are only intended to allow user agents to support legacy content.

   <dt>Status

   <dd>
    <p>One of the following:</p>

    <dl>
     <dt>Proposal

     <dd>The name has not received wide peer review and approval. Someone has
      proposed it and is using it.

     <dt>Accepted

     <dd>The name has received wide peer review and approval. It has a
      specification that unambiguously defines how to handle pages that use
      the name, including when they use it in incorrect ways.

     <dt>Unendorsed

     <dd>The metadata name has received wide peer review and it has been
      found wanting. Existing pages are using this keyword, but new pages
      should avoid it. The "brief description" and "link to more details"
      entries will give details of what authors should use instead, if
      anything.
    </dl>

    <p>If a metadata name is added with the "proposal" status and found to be
     redundant with existing values, it should be removed and listed as a
     synonym for the existing value.</p>
  </dl>

  <p>Conformance checkers must use the information given on the WHATWG Wiki
   MetaExtensions page to establish if a value not explicitly defined in this
   specification is allowed or not. When an author uses a new type not
   defined by either this specification or the Wiki page, conformance
   checkers should offer to add the value to the Wiki, with the details
   described above, with the "proposal" status.

  <p>This specification does not define how new values will get approved. It
   is expected that the Wiki will have a community that addresses this.

  <p>Metadata names whose values are to be URIs must not be proposed or
   accepted. Links must be represented using the <code><a
   href="#link">link</a></code> element, not the <code><a
   href="#meta0">meta</a></code> element.

  <h5 id=pragma><span class=secno>3.7.5.3. </span>Pragma directives</h5>

  <p>When the <dfn id=http-equiv
   title=attr-meta-http-equiv><code>http-equiv</code></dfn> attribute is
   specified on a <code><a href="#meta0">meta</a></code> element, the element
   is a pragma directive.

  <p>The <dfn id=http-equiv0
   title=attr-meta-http-equiv><code>http-equiv</code></dfn> attribute is an
   <a href="#enumerated">enumerated attribute</a>. The following table lists
   the keywords defined for this attribute. The states given in the first
   cell of the the rows with keywords give the states to which those keywords
   map.<!-- Some of the keywords are non-conforming, as
  noted in the last column.-->

  <table>
   <thead>
    <tr>
     <th>State

     <th>Keywords <!--     <th>Notes-->

   <tbody><!-- things that are neither conforming nor do anything are commented out
    <tr>
     <td><span title="attr-meta-http-equiv-content-language">Content-Language</span>
     <td><code title="">Content-Language</code>
     <td>Non-conforming
    <tr>
     <td><span title="attr-meta-http-equiv-content-type">Content-Type</span>
     <td><code title="">Content-Type</code>
     <td>Non-conforming
    <tr>
     <td><span title="attr-meta-http-equiv-content-script-type">Content-Script-Type</span>
     <td><code title="">Content-Script-Type</code>
     <td>Non-conforming
    <tr>
     <td><span title="attr-meta-http-equiv-content-style-type">Content-Style-Type</span>
     <td><code title="">Content-Style-Type</code>
     <td>Non-conforming
-->

    <tr>
     <td><a href="#refresh" title=attr-meta-http-equiv-refresh>Refresh</a>

     <td><code title="">refresh</code> <!--     <td>-->

    <tr>
     <td><a href="#default" title=attr-meta-http-equiv-default-style>Default
      style</a>

     <td><code title="">default-style</code> <!--     <td>-->
  </table>

  <p>When a <code><a href="#meta0">meta</a></code> element is inserted into
   the document, if its <code title=attr-meta-http-equiv><a
   href="#http-equiv0">http-equiv</a></code> attribute is present and
   represents one of the above states, then the user agent must run the
   algorithm appropriate for that state, as described in the following list:

  <dl>
   <dt><dfn id=refresh title=attr-meta-http-equiv-refresh>Refresh state</dfn>
    

   <dd>
    <ol><!-- TESTS: http://www.hixie.ch/tests/adhoc/html/meta/refresh/ -->

     <li>
      <p>If another <code><a href="#meta0">meta</a></code> element in the <a
       href="#refresh" title=attr-meta-http-equiv-refresh>Refresh state</a>
       has already been successfully processed (i.e. when it was inserted the
       user agent processed it and reached the last step of this list of
       steps), then abort these steps.

     <li>
      <p>If the <code><a href="#meta0">meta</a></code> element has no <code
       title=attr-meta-content><a href="#content0">content</a></code>
       attribute, or if that attribute's value is the empty string, then
       abort these steps.

     <li>
      <p>Let <var title="">input</var> be the value of the element's <code
       title=attr-meta-content><a href="#content0">content</a></code>
       attribute.

     <li>
      <p>Let <var title="">position</var> point at the first character of
       <var title="">input</var>.

     <li>
      <p><a href="#skip-whitespace">Skip whitespace</a>.

     <li>
      <p><a href="#collect" title="collect a sequence of characters">Collect
       a sequence of characters</a> in the range U+0030 DIGIT ZERO to U+0039
       DIGIT NINE, and parse the resulting string using the <a
       href="#rules">rules for parsing non-negative integers</a>. If the
       sequence of characters collected is the empty string, then no number
       will have been parsed; abort these steps. Otherwise, let <var
       title="">time</var> be the parsed number.

     <li>
      <p><a href="#collect" title="collect a sequence of characters">Collect
       a sequence of characters</a> in the range U+0030 DIGIT ZERO to U+0039
       DIGIT NINE and U+002E FULL STOP ("<code title="">.</code>"). Ignore
       any collected characters.

     <li>
      <p><a href="#skip-whitespace">Skip whitespace</a>.

     <li>
      <p>Let <var title="">url</var> be the address of the current page.

     <li>
      <p>If the character in <var title="">input</var> pointed to by <var
       title="">position</var> is a U+003B SEMICOLON ("<code
       title="">;</code>"), then advance <var title="">position</var> to the
       next character. Otherwise, jump to the last step.

     <li>
      <p><a href="#skip-whitespace">Skip whitespace</a>.

     <li>
      <p>If the character in <var title="">input</var> pointed to by <var
       title="">position</var> is one of U+0055 LATIN CAPITAL LETTER U or
       U+0075 LATIN SMALL LETTER U, then advance <var title="">position</var>
       to the next character. Otherwise, jump to the last step.

     <li>
      <p>If the character in <var title="">input</var> pointed to by <var
       title="">position</var> is one of U+0052 LATIN CAPITAL LETTER R or
       U+0072 LATIN SMALL LETTER R, then advance <var title="">position</var>
       to the next character. Otherwise, jump to the last step.

     <li>
      <p>If the character in <var title="">input</var> pointed to by <var
       title="">position</var> is one of U+004C LATIN CAPITAL LETTER L or
       U+006C LATIN SMALL LETTER L, then advance <var title="">position</var>
       to the next character. Otherwise, jump to the last step.

     <li>
      <p><a href="#skip-whitespace">Skip whitespace</a>.

     <li>
      <p>If the character in <var title="">input</var> pointed to by <var
       title="">position</var> is a U+003D EQUALS SIGN ("<code
       title="">=</code>"), then advance <var title="">position</var> to the
       next character. Otherwise, jump to the last step.

     <li>
      <p><a href="#skip-whitespace">Skip whitespace</a>.

     <li>
      <p>Let <var title="">url</var> be equal to the substring of <var
       title="">input</var> from the character at <var
       title="">position</var> to the end of the string.

     <li>
      <p>Strip any trailing <a href="#space" title="space character">space
       characters</a> from the end of <var title="">url</var>.

     <li>
      <p>Strip any U+0009 CHARACTER TABULATION, U+000A LINE FEED (LF), and
       U+000D CARRIAGE RETURN (CR) characters from <var title="">url</var>.

     <li>
      <p>Resolve the <var title="">url</var> value to an absolute URI using
       the base URI of the <code><a href="#meta0">meta</a></code> element.

     <li>
      <p>Set a timer so that in <var title="">time</var> seconds, if the user
       has not canceled the redirect, the user agent <a href="#navigate"
       title=navigate>navigates</a> to <var title="">url</var>, with <a
       href="#replacement">replacement enabled</a>.
    </ol>

    <p>For <code><a href="#meta0">meta</a></code> elements in the <a
     href="#refresh" title=attr-meta-http-equiv-refresh>Refresh state</a>,
     the <code title=attr-meta-content><a href="#content0">content</a></code>
     attribute must have a value consisting either of:

    <ul>
     <li> just a <a href="#valid">valid non-negative integer</a>, or

     <li> a <a href="#valid">valid non-negative integer</a>, followed by a
      U+003B SEMICOLON (<code title="">;</code>), followed by one or more <a
      href="#space" title="space character">space characters</a>, followed by
      either a U+0055 LATIN CAPITAL LETTER U or a U+0075 LATIN SMALL LETTER
      U, a U+0052 LATIN CAPITAL LETTER R or a U+0072 LATIN SMALL LETTER R, a
      U+004C LATIN CAPITAL LETTER L or a U+006C LATIN SMALL LETTER L, a
      U+003D EQUALS SIGN (<code title="">=</code>), and then a valid URI (or
      IRI).
    </ul>

    <p>In the former case, the integer represents a number of seconds before
     the page is to be reloaded; in the latter case the integer represents a
     number of seconds before the page is to be replaced by the page at the
     given URI.</p>

   <dd>

   <dt><dfn id=default title=attr-meta-http-equiv-default-style>Default style
    state</dfn>

   <dd>
    <ol>
     <li class=big-issue>...
    </ol>

   <dd>
  </dl>

  <h5 id=charset><span class=secno>3.7.5.4. </span>Specifying and
   establishing the document's character encoding</h5>

  <p>The <code><a href="#meta0">meta</a></code> element may also be used to
   provide UAs with character encoding information for <a href="#html5"
   title=HTML5>HTML</a> files, by setting the <dfn id=charset0
   title=attr-meta-charset><code>charset</code></dfn> attribute to the name
   of a character encoding. This is called a character encoding declaration.

  <p>The following restrictions apply to character encoding declarations:

  <ul>
   <li>When <a href="#syntax">serialised</a>, the <code
    title=attr-meta-charset><a href="#charset0">charset</a></code> attribute
    and its value must be contained completely in the first 512 bytes of the
    file.

   <li>The attribute value must be serialised without the use of character
    entity references of any kind.

   <li>The value must be a valid character encoding name. <a
    href="#refsIANACHARSET">[IANACHARSET]</a> <!-- XXX
   http://www.iana.org/assignments/character-sets -->

   <li>The character encoding name given must be the name of the character
    encoding used to serialise the file.

   <li>The character encoding used must be a superset of US-ASCII
    (specifically, ANSI_X3.4-1968) for bytes in the range 0x09 - 0x0D, 0x20,
    0x21, 0x22, 0x26, 0x27, 0x2C - 0x3F, 0x41 - 0x5A, and 0x61 - 0x7A.</li>
   <!-- XXX #refs RFC1345 ? -->
   <!-- is that list ok? do
   any character sets we want to support do things outside that range?
   -->
  </ul>

  <p>If the encoding is one of UTF-8, UTF-16BE, UTF-16LE, UTF-32BE, or
   UTF-32LE, then authors can use a BOM at the start of the file to indicate
   the character encoding.</p>
  <!-- UTF-EBCDIC, too! -->

  <p>In XHTML, the XML declaration should be used for inline character
   encoding information, if necessary.

  <h4 id=the-style><span class=secno>3.7.6. </span>The <dfn
   id=style><code>style</code></dfn> element</h4>

  <p><a href="#metadata" title="metadata elements">Metadata element</a>.

  <dl class=element>
   <dt>Contexts in which this element may be used:

   <dd>In a <code><a href="#head">head</a></code> element.

   <dd>At the start of <code><a href="#article">article</a></code>, <code><a
    href="#aside">aside</a></code>, <code><a href="#div">div</a></code>, and
    <code><a href="#section">section</a></code> elements.

   <dt>Content model:

   <dd>Depends on the value of the <code title=attr-style-type><a
    href="#type1">type</a></code> attribute.

   <dt>Element-specific attributes:

   <dd><code title=attr-style-media><a href="#media2">media</a></code>

   <dd><code title=attr-style-type><a href="#type1">type</a></code>

   <dd><code title=attr-style-scoped><a href="#scoped">scoped</a></code>

   <dd>Also, the <code title=attr-style-title><a
    href="#title3">title</a></code> attribute has special semantics on this
    element.

   <dt>DOM interface:

   <dd>
    <pre
     class=idl>interface <dfn id=htmlstyleelement>HTMLStyleElement</dfn> : <a href="#htmlelement">HTMLElement</a> {
           attribute boolean <code title=dom-style-disabled><a href="#disabled0">disabled</a></code>;
           attribute DOMString <code title=dom-style-media><a href="#media3">media</a></code>;
           attribute DOMString <code title=dom-style-type><a href="#type2">type</a></code>;
           attribute boolean <code title=dom-style-scoped><a href="#scoped0">scoped</a></code>;
};</pre>

    <p>The <code>LinkStyle</code> interface must also be implemented by this
     element, the <a href="#styling0">styling processing model</a> defines
     how. <a href="#refsCSSOM">[CSSOM]</a></p>
  </dl>

  <p>The <code><a href="#style">style</a></code> element allows authors to
   embed style information in their documents. The <code><a
   href="#style">style</a></code> element is one of several inputs to the <a
   href="#styling0">styling processing model</a>.

  <p>If the <dfn id=type1 title=attr-style-type><code>type</code></dfn>
   attribute is given, it must contain a valid MIME type, optionally with
   parameters, that designates a styling language. <a
   href="#refsRFC2046">[RFC2046]</a> If the attribute is absent, the type
   defaults to <code>text/css</code>. <a href="#refsRFC2318">[RFC2138]</a></p>
  <!-- XXX this is the second time we have this paragraph here... -->

  <p>When examining types to determine if they support the language, user
   agents must not ignore unknown MIME parameters &mdash; types with unknown
   parameters must be assumed to be unsupported.

  <p>The <dfn id=media2 title=attr-style-media><code>media</code></dfn>
   attribute says which media the styles apply to. The value must be a valid
   media query. <a href="#refsMQ">[MQ]</a> User agents must only apply the
   styles to <span>views</span> while their state match the listed media. <a
   href="#refsDOM3VIEWS">[DOM3VIEWS]</a>

  <p id=style-default-media>The default, if the <code
   title=attr-style-media><a href="#media2">media</a></code> attribute is
   omitted, is <code>all</code>, meaning that by default styles apply to all
   media.

  <p>The <dfn id=scoped title=attr-style-scoped><code>scoped</code></dfn>
   attribute is a <a href="#boolean0">boolean attribute</a>. If the attribute
   is present, then the user agent must only apply the specified style
   information to the <code><a href="#style">style</a></code> element's
   parent element (if any), and that element's child nodes. Otherwise, the
   specified styles must, if applied, be applied to the entire document.

  <p id=title-on-style>The <dfn id=title3
   title=attr-style-title><code>title</code></dfn> attribute on <code><a
   href="#style">style</a></code> elements defines <a
   href="#alternative">alternative style sheet sets</a>. If the <code><a
   href="#style">style</a></code> element has no <code
   title=attr-style-title><a href="#title3">title</a></code> attribute, then
   it has no title; the <code title=attr-title><a
   href="#title">title</a></code> attribute of ancestors does not apply to
   the <code><a href="#style">style</a></code> element.</p>
  <!--
  XXX xref -->

  <p class=note>The <code title=attr-style-title><a
   href="#title3">title</a></code> attribute on <code><a
   href="#style">style</a></code> elements, like the <code
   title=attr-link-title><a href="#title2">title</a></code> attribute on
   <code><a href="#link">link</a></code> elements, differs from the global
   <code title=attr-title><a href="#title">title</a></code> attribute in that
   a <code><a href="#style">style</a></code> block without a title does not
   inherit the title of the parent element: it merely has no title.

  <p>All descendant elements must be processed, according to their semantics,
   before the <code><a href="#style">style</a></code> element itself is
   evaluated. For styling languages that consist of pure text, user agents
   must evaluate <code><a href="#style">style</a></code> elements by passing
   the concatenation of the contents of all the <a href="#text-node"
   title="text node">text nodes</a> that are direct children of the <code><a
   href="#style">style</a></code> element (not any other nodes such as
   comments or elements), in <a href="#tree-order">tree order</a>, to the
   style system. For XML-based styling languages, user agents must pass all
   the children nodes of the <code><a href="#style">style</a></code> element
   to the style system.

  <p class=note>This specification does not specify a style system, but CSS
   is expected to be supported by most Web browsers. <a
   href="#refsCSS21">[CSS21]</a>

  <p>The <dfn id=media3 title=dom-style-media><code>media</code></dfn>, <dfn
   id=type2 title=dom-style-type><code>type</code></dfn> and <dfn id=scoped0
   title=dom-style-scoped><code>scoped</code></dfn> DOM attributes must <a
   href="#reflect">reflect</a> the respective content attributes of the same
   name.

  <p>The DOM <dfn id=disabled0
   title=dom-style-disabled><code>disabled</code></dfn> attribute behaves as
   defined <a href="#disabled1" title=dom-linkstyle-disabled>for the
   alternative style sheets DOM</a>.

  <h4 id=styling><span class=secno>3.7.7. </span><dfn id=styling0
   title="styling processing model">Styling</dfn></h4>

  <p>The <code><a href="#link">link</a></code> and <code><a
   href="#style">style</a></code> elements can provide styling information
   for the user agent to use when rendering the document. The DOM Styling
   specification specifies what styling information is to be used by the user
   agent and how it is to be used. <a href="#refsCSSOM">[CSSOM]</a>

  <p>The <code><a href="#style">style</a></code> and <code><a
   href="#link">link</a></code> elements implement the <code>LinkStyle</code>
   interface. <a href="#refsCSSOM">[CSSOM]</a>

  <p>For <code><a href="#style">style</a></code> elements, if the user agent
   does not support the specified styling language, then the <code
   title=dom-LinkStyle-sheet>sheet</code> attribute of the element's
   <code>LinkStyle</code> interface must return null. Similarly, <code><a
   href="#link">link</a></code> elements that do not represent <a
   href="#stylesheet" title=rel-stylesheet>external resource links that
   contribute to the styling processing model</a> (i.e. that do not have a
   <code title=rel-stylesheet><a href="#stylesheet">stylesheet</a></code>
   keyword in their <code title=attr-link-rel><a href="#rel">rel</a></code>
   attribute), and <code><a href="#link">link</a></code> elements whose
   specified resource has not yet been downloaded, or is not in a supported
   styling language, must have their <code>LinkStyle</code> interface's <code
   title=dom-LinkStyle-sheet>sheet</code> attribute return null.

  <p>Otherwise, the <code>LinkStyle</code> interface's <code
   title=dom-LinkStyle-sheet>sheet</code> attribute must return a
   <code>StyleSheet</code> object with the attributes implemented as follows:
   <a href="#refsCSSOM">[CSSOM]</a>

  <dl>
   <dt>The content type (<code title=dom-stylesheet-type>type</code> DOM
    attribute)

   <dd>
    <p>The content type must be the same as the style's specified type. For
     <code><a href="#style">style</a></code> elements, this is the same as
     the <code title=attr-style-type><a href="#type1">type</a></code> content
     attribute's value, or <code title="">text/css</code> if that is omitted.
     For <code><a href="#link">link</a></code> elements, this is the <a
     href="#content-type8" title=Content-Type>Content-Type metadata of the
     specified resource</a>.

   <dt>The location (<code title=dom-stylesheet-href>href</code> DOM
    attribute)

   <dd>
    <p>For <code><a href="#link">link</a></code> elements, the location must
     be the URI given by the element's <code title=attr-link-href><a
     href="#href1">href</a></code> content attribute. For <code><a
     href="#style">style</a></code> elements, there is no location.

   <dt>The intended destination media for style information (<code
    title=dom-stylesheet-media>media</code> DOM attribute)

   <dd>
    <p>The media must be the same as the value of the element's <code
     title="">media</code> content attribute.

   <dt>The style sheet title (<code title=dom-stylesheet-title>title</code>
    DOM attribute)

   <dd>
    <p>The title must be the same as the value of the element's <code
     title="">title</code> content attribute. If the attribute is absent,
     then the style sheet does not have a title. The title is used for
     defining <dfn id=alternative>alternative style sheet sets</dfn>.
  </dl>

  <p>The <dfn id=disabled1
   title=dom-LinkStyle-disabled><code>disabled</code></dfn> DOM attribute on
   <code><a href="#link">link</a></code> and <code><a
   href="#style">style</a></code> elements must return false and do nothing
   on setting, if the <code title=dom-linkstyle-sheet>sheet</code> attribute
   of their <code>LinkStyle</code> interface is null. Otherwise, it must
   return the value of the <code>StyleSheet</code> interface's <code
   title=dom-stylesheet-disabled>disabled</code> attribute on getting, and
   forward the new value to that same attribute on setting.</p>
  <!-- <p class="big-issue">Need more here - defining preferred
  stylesheets, alternative stylesheets, persistent stylesheets, ordering
  of stylesheets, dynamic additions/removals, how it maps to
  .styleSheets, HTTP Link: headers, and the stuff about the alternative
  stylesheet API.</p> XXX that will all be covered by Anne's spec -->

  <h3 id=sections><span class=secno>3.8. </span>Sections</h3>

  <p><dfn id=sectioning>Sectioning elements</dfn> are elements that divide
   the page into, for lack of a better word, sections. This section describes
   HTML's sectioning elements and elements that support them.

  <p id=applyToSection>Some elements are scoped to their nearest ancestor
   sectioning element. For example, <code><a
   href="#address">address</a></code> elements apply just to their section.
   For such elements <var title="">x</var>, the elements that apply to a
   sectioning element <var title="">e</var> are all the <var title="">x</var>
   elements whose nearest sectioning element is <var title="">e</var>.

  <h4 id=the-body><span class=secno>3.8.1. </span>The <dfn
   id=body0><code>body</code></dfn> element</h4>

  <p><a href="#sectioning" title="sectioning elements">Sectioning
   element</a>.

  <dl class=element>
   <dt>Contexts in which this element may be used:

   <dd>As the second element in an <code><a href="#html">html</a></code>
    element.

   <dt>Content model:

   <dd>Zero or more <a href="#block-level0">block-level elements</a>.

   <dt>Element-specific attributes:

   <dd>None.

   <dt>DOM interface:

   <dd>No difference from <code><a
    href="#htmlelement">HTMLElement</a></code>.
  </dl>

  <p>The <code><a href="#body0">body</a></code> element represents the main
   content of the document.

  <p>The <code><a href="#body0">body</a></code> element potentially has a
   heading. See the section on <a href="#headings0">headings and sections</a>
   for further details.

  <p>In conforming documents, there is only one <code><a
   href="#body0">body</a></code> element. The <code
   title=dom-document-body><a href="#body">document.body</a></code> DOM
   attribute provides scripts with easy access to a document's <code><a
   href="#body0">body</a></code> element.

  <p class=note>Some DOM operations (for example, parts of the <a
   href="#drag-and">drag and drop</a> model) are defined in terms of "<a
   href="#the-body0">the body element</a>". This refers to a particular
   element in the DOM, as per the definition of the term, and not any
   arbitrary <code><a href="#body0">body</a></code> element.

  <h4 id=the-section><span class=secno>3.8.2. </span>The <dfn
   id=section><code>section</code></dfn> element</h4>

  <p><a href="#sectioning" title="sectioning elements">Sectioning</a> <a
   href="#block-level0" title="block-level elements">block-level element</a>.

  <dl class=element>
   <dt>Contexts in which this element may be used:

   <dd>Where <a href="#block-level0">block-level elements</a> are expected.

   <dt>Content model:

   <dd>Zero or more <code><a href="#style">style</a></code> elements,
    followed by zero or more <a href="#block-level0">block-level
    elements</a>.

   <dt>Element-specific attributes:

   <dd>None.

   <dt>DOM interface:

   <dd>No difference from <code><a
    href="#htmlelement">HTMLElement</a></code>.
  </dl>

  <p>The <code><a href="#section">section</a></code> element represents a
   generic document or application section. A section, in this context, is a
   thematic grouping of content, typically with a header, possibly with a
   footer.

  <p class=example>Examples of sections would be chapters, the various tabbed
   pages in a tabbed dialog box, or the numbered sections of a thesis. A Web
   site's home page could be split into sections for an introduction, news
   items, contact information.

  <p>Each <code><a href="#section">section</a></code> element potentially has
   a heading. See the section on <a href="#headings0">headings and
   sections</a> for further details.

  <h4 id=the-nav><span class=secno>3.8.3. </span>The <dfn
   id=nav><code>nav</code></dfn> element</h4>

  <p><a href="#sectioning" title="sectioning elements">Sectioning</a> <a
   href="#block-level0" title="block-level elements">block-level element</a>.

  <dl class=element>
   <dt>Contexts in which this element may be used:

   <dd>Where <a href="#block-level0">block-level elements</a> are expected.

   <dt>Content model:

   <dd>Zero or more <a href="#block-level0">block-level elements</a>, or <a
    href="#inline-level0">inline-level content</a> (but not both).

   <dt>Element-specific attributes:

   <dd>None.

   <dt>DOM interface:

   <dd>No difference from <code><a
    href="#htmlelement">HTMLElement</a></code>.
  </dl>

  <p>The <code><a href="#nav">nav</a></code> element represents a section of
   a page that links to other pages or to parts within the page: a section
   with navigation links.

  <p>When <a href="#determining0" title="Determining if a particular element
   contains block-level elements or inline-level content">used as an
   inline-level content</a> container, the element represents a <a
   href="#paragraph">paragraph</a>.

  <p>Each <code><a href="#nav">nav</a></code> element potentially has a
   heading. See the section on <a href="#headings0">headings and sections</a>
   for further details.

  <h4 id=the-article><span class=secno>3.8.4. </span>The <dfn
   id=article><code>article</code></dfn> element</h4>

  <p><a href="#sectioning" title="sectioning elements">Sectioning</a> <a
   href="#block-level0" title="block-level elements">block-level element</a>.

  <dl class=element>
   <dt>Contexts in which this element may be used:

   <dd>Where <a href="#block-level0">block-level elements</a> are expected.

   <dt>Content model:

   <dd>Zero or more <code><a href="#style">style</a></code> elements,
    followed by zero or more <a href="#block-level0">block-level
    elements</a>.

   <dt>Element-specific attributes:

   <dd>None.</dd>
   <!--
XXX attributes to give the date authored, date published
-->

   <dt>DOM interface:

   <dd>No difference from <code><a
    href="#htmlelement">HTMLElement</a></code>.
  </dl>

  <p>The <code><a href="#article">article</a></code> element represents a
   section of a page that consists of a composition that forms an independent
   part of a document, page, or site. This could be a forum post, a magazine
   or newspaper article, a Web log entry, a user-submitted comment, or any
   other independent item of content.

  <p class=note>An <code><a href="#article">article</a></code> element is
   "independent" in that its contents could stand alone, for example in
   syndication. However, the element is still associated with its ancestors;
   for instance, contact information that <a
   href="#applyToSection">applies</a> to a parent <code><a
   href="#body0">body</a></code> element still covers the <code><a
   href="#article">article</a></code> as well.

  <p>When <code><a href="#article">article</a></code> elements are nested,
   the inner <code><a href="#article">article</a></code> elements represent
   articles that are in principle related to the contents of the outer
   article. For instance, a Web log entry on a site that accepts
   user-submitted comments could represent the comments as <code><a
   href="#article">article</a></code> elements nested within the <code><a
   href="#article">article</a></code> element for the Web log entry.

  <p>Author information associated with an <code><a
   href="#article">article</a></code> element (q.v. the <code><a
   href="#address">address</a></code> element) does not apply to nested
   <code><a href="#article">article</a></code> elements.

  <p>Each <code><a href="#article">article</a></code> element potentially has
   a heading. See the section on <a href="#headings0">headings and
   sections</a> for further details.

  <h4 id=the-blockquote><span class=secno>3.8.5. </span>The <dfn
   id=blockquote><code>blockquote</code></dfn> element</h4>

  <p><a href="#sectioning" title="sectioning elements">Sectioning</a> <a
   href="#block-level0" title="block-level elements">block-level element</a>,
   and <a href="#structured" title="structured inline-level
   elements">structured inline-level element</a>.

  <dl class=element>
   <dt>Contexts in which this element may be used:

   <dd>Where <a href="#block-level0">block-level elements</a> are expected.

   <dd>Where <a href="#structured">structured inline-level elements</a> are
    allowed.

   <dt>Content model:

   <dd>Zero or more <a href="#block-level0">block-level elements</a>.

   <dt>Element-specific attributes:

   <dd><code title=attr-blockquote-cite><a href="#cite">cite</a></code>

   <dt>DOM interface:

   <dd>
    <pre
     class=idl>interface <dfn id=htmlquoteelement>HTMLQuoteElement</dfn> : <a href="#htmlelement">HTMLElement</a> {
           attribute DOMString <a href="#cite0" title=dom-quote-cite>cite</a>;
};</pre>

    <p class=note>The <code><a
     href="#htmlquoteelement">HTMLQuoteElement</a></code> interface is also
     used by the <code><a href="#q">q</a></code> element.</p>
  </dl>

  <p>The <code><a href="#blockquote">blockquote</a></code> element represents
   a section that is quoted from another source.

  <p>Content inside a <code><a href="#blockquote">blockquote</a></code> must
   be quoted from another source, whose URI, if it has one, should be cited
   in the <dfn id=cite title=attr-blockquote-cite><code>cite</code></dfn>
   attribute.

  <p>If the <code title=attr-blockquote-cite><a href="#cite">cite</a></code>
   attribute is present, it must be a URI (or IRI). User agents should allow
   users to follow such citation links.

  <p>If a <code><a href="#blockquote">blockquote</a></code> element is <a
   href="#preceeded">preceeded or followed</a> by a <code><a
   href="#p">p</a></code> element that contains a single <code><a
   href="#cite2">cite</a></code> element and is itself not <a
   href="#preceeded">preceeded or followed</a> by another <code><a
   href="#blockquote">blockquote</a></code> element and does not itself have
   a <code><a href="#q">q</a></code> element descendant, then, the citation
   given by that <code><a href="#cite2">cite</a></code> element gives the
   source of the quotation contained in the <code><a
   href="#blockquote">blockquote</a></code> element.

  <p>Each <code><a href="#blockquote">blockquote</a></code> element
   potentially has a heading. See the section on <a
   href="#headings0">headings and sections</a> for further details.

  <p>The <dfn id=cite0 title=dom-quote-cite><code>cite</code></dfn> DOM
   attribute <code>reflects</code> the element's <code title="">cite</code>
   content attribte.

  <p class=note>The best way to represent a conversation is not with the
   <code><a href="#cite2">cite</a></code> and <code><a
   href="#blockquote">blockquote</a></code> elements, but with the <code><a
   href="#dialog">dialog</a></code> element.

  <h4 id=the-aside><span class=secno>3.8.6. </span>The <dfn
   id=aside><code>aside</code></dfn> element</h4>

  <p><a href="#sectioning" title="sectioning elements">Sectioning</a> <a
   href="#block-level0" title="block-level elements">block-level element</a>.

  <dl class=element>
   <dt>Contexts in which this element may be used:

   <dd>Where <a href="#block-level0">block-level elements</a> are expected.

   <dt>Content model:

   <dd>Zero or more <code><a href="#style">style</a></code> elements,
    followed by either zero or more <a href="#block-level0">block-level
    elements</a>, or <a href="#inline-level0">inline-level content</a> (but
    not both).

   <dt>Element-specific attributes:

   <dd>None.

   <dt>DOM interface:

   <dd>No difference from <code><a
    href="#htmlelement">HTMLElement</a></code>.
  </dl>

  <p>The <code><a href="#aside">aside</a></code> element represents a section
   of a page that consists of content that is tangentially related to the
   content around the <code><a href="#aside">aside</a></code> element, and
   which could be considered separate from that content. Such sections are
   often represented as sidebars in printed typography.

  <p>When <a href="#determining0" title="Determining if a particular element
   contains block-level elements or inline-level content">used as an
   inline-level content</a> container, the element represents a <a
   href="#paragraph">paragraph</a>.

  <p>Each <code><a href="#aside">aside</a></code> element potentially has a
   heading. See the section on <a href="#headings0">headings and sections</a>
   for further details.

  <h4 id=the-h1><span class=secno>3.8.7. </span>The <dfn
   id=h1><code>h1</code></dfn>, <dfn id=h2><code>h2</code></dfn>, <dfn
   id=h3><code>h3</code></dfn>, <dfn id=h4><code>h4</code></dfn>, <dfn
   id=h5><code>h5</code></dfn>, and <dfn id=h6><code>h6</code></dfn> elements</h4>

  <p><a href="#block-level0">Block-level elements</a>.

  <dl class=element>
   <dt>Contexts in which these elements may be used:

   <dd>Where <a href="#block-level0">block-level elements</a> are expected.

   <dt>Content model:

   <dd><a href="#significant" title="significant inline
    content">Significant</a> <a href="#strictly">strictly inline-level
    content</a>.

   <dt>Element-specific attributes:

   <dd>None.

   <dt>DOM interface:

   <dd>No difference from <code><a
    href="#htmlelement">HTMLElement</a></code>.
  </dl>

  <p>These elements define headers for their sections.

  <p>The semantics and meaning of these elements are defined in the section
   on <a href="#headings0">headings and sections</a>.

  <p>These elements have a <dfn id=rank>rank</dfn> given by the number in
   their name. The <code><a href="#h1">h1</a></code> element is said to have
   the highest rank, the <code><a href="#h6">h6</a></code> element has the
   lowest rank, and two elements with the same name have equal rank.

  <p>These elements must not be <a href="#significant" title="significant
   inline content">empty</a>.

  <h4 id=the-header><span class=secno>3.8.8. </span>The <dfn
   id=header><code>header</code></dfn> element</h4>

  <p><a href="#block-level0" title="block-level elements">Block-level
   element</a>.

  <dl class=element>
   <dt>Contexts in which this element may be used:

   <dd>Where <a href="#block-level0">block-level elements</a> are expected
    and there are no <code><a href="#header">header</a></code> ancestors.

   <dt>Content model:

   <dd>Zero or more <a href="#block-level0">block-level elements</a>,
    including at least one descendant <code><a href="#h1">h1</a></code>,
    <code><a href="#h2">h2</a></code>, <code><a href="#h3">h3</a></code>,
    <code><a href="#h4">h4</a></code>, <code><a href="#h5">h5</a></code>, or
    <code><a href="#h6">h6</a></code> element, but no <span>sectioning
    element</span> descendants, no <code><a href="#header">header</a></code>
    element descendants, and no <code><a href="#footer">footer</a></code>
    element descendants.

   <dt>Element-specific attributes:

   <dd>None.

   <dt>DOM interface:

   <dd>No difference from <code><a
    href="#htmlelement">HTMLElement</a></code>.
  </dl>

  <p>The <code><a href="#header">header</a></code> element represents the
   header of a section. Headers may contain more than just the section's
   heading &mdash; for example it would be reasonable for the header to
   include version history information.

  <p><code><a href="#header">header</a></code> elements must not contain any
   <code><a href="#header">header</a></code> elements, <code><a
   href="#footer">footer</a></code> elements, or any sectioning elements
   (such as <code><a href="#section">section</a></code>) as descendants.

  <p><code><a href="#header">header</a></code> elements must have at least
   one <code><a href="#h1">h1</a></code>, <code><a href="#h2">h2</a></code>,
   <code><a href="#h3">h3</a></code>, <code><a href="#h4">h4</a></code>,
   <code><a href="#h5">h5</a></code>, or <code><a href="#h6">h6</a></code>
   element as a descendant.

  <p>For the purposes of document summaries, outlines, and the like, <code><a
   href="#header">header</a></code> elements are equivalent to the highest <a
   href="#rank" title=rank>ranked</a> <code><a
   href="#h1">h1</a></code>-<code><a href="#h6">h6</a></code> element
   descendant (the first such element if there are multiple elements with
   that <a href="#rank">rank</a>).

  <p>Other heading elements indicate subheadings or subtitles.

  <div class=example>
   <p>Here are some examples of valid headers. In each case, the emphasised
    text represents the text that would be used as the header in an
    application extracting header data and ignoring subheadings.</p>

   <pre>&lt;header&gt;
 &lt;h1&gt;<strong>The reality dysfunction</strong>&lt;/h1&gt;
 &lt;h2&gt;Space is not the only void&lt;/h2&gt;
&lt;/header&gt;</pre>

   <pre>&lt;header&gt;
 &lt;p&gt;Welcome to...&lt;/p&gt;
 &lt;h1&gt;<strong>Voidwars!</strong>&lt;/h1&gt;
&lt;/header&gt;</pre>

   <pre>&lt;header&gt;
 &lt;h1&gt;<strong>Scalable Vector Graphics (SVG) 1.2</strong>&lt;/h1&gt;
 &lt;h2&gt;W3C Working Draft 27 October 2004&lt;/h2&gt;
 &lt;dl&gt;
  &lt;dt&gt;This version:&lt;/dt&gt;
  &lt;dd&gt;&lt;a href="http://www.w3.org/TR/2004/WD-SVG12-20041027/"&gt;http://www.w3.org/TR/2004/WD-SVG12-20041027/&lt;/a&gt;&lt;/dd&gt;
  &lt;dt&gt;Previous version:&lt;/dt&gt;
  &lt;dd&gt;&lt;a href="http://www.w3.org/TR/2004/WD-SVG12-20040510/"&gt;http://www.w3.org/TR/2004/WD-SVG12-20040510/&lt;/a&gt;&lt;/dd&gt;
  &lt;dt&gt;Latest version of SVG 1.2:&lt;/dt&gt;
  &lt;dd&gt;&lt;a href="http://www.w3.org/TR/SVG12/"&gt;http://www.w3.org/TR/SVG12/&lt;/a&gt;&lt;/dd&gt;
  &lt;dt&gt;Latest SVG Recommendation:&lt;/dt&gt;
  &lt;dd&gt;&lt;a href="http://www.w3.org/TR/SVG/"&gt;http://www.w3.org/TR/SVG/&lt;/a&gt;&lt;/dd&gt;
  &lt;dt&gt;Editor:&lt;/dt&gt;
  &lt;dd&gt;Dean Jackson, W3C, &lt;a href="mailto:dean@w3.org"&gt;dean@w3.org&lt;/a&gt;&lt;/dd&gt;
  &lt;dt&gt;Authors:&lt;/dt&gt;
  &lt;dd&gt;See &lt;a href="#authors"&gt;Author List&lt;/a&gt;&lt;/dd&gt;
 &lt;/dl&gt;
 &lt;p class="copyright"&gt;&lt;a href="http://www.w3.org/Consortium/Legal/ipr-notic <em>...</em>
&lt;/header&gt;</pre>
  </div>

  <p>The section on <a href="#headings0">headings and sections</a> defines
   how <code><a href="#header">header</a></code> elements are assigned to
   individual sections.

  <p>The <a href="#rank">rank</a> of a <code><a
   href="#header">header</a></code> element is the same as for an <code><a
   href="#h1">h1</a></code> element (the highest rank).

  <h4 id=the-footer><span class=secno>3.8.9. </span>The <dfn
   id=footer><code>footer</code></dfn> element</h4>

  <p><a href="#block-level0" title="block-level elements">Block-level
   element</a>.

  <dl class=element>
   <dt>Contexts in which this element may be used:

   <dd>Where <a href="#block-level0">block-level elements</a> are expected.

   <dt>Content model:

   <dd>Either zero or more <a href="#block-level0">block-level elements</a>,
    but with no <code><a href="#h1">h1</a></code>, <code><a
    href="#h2">h2</a></code>, <code><a href="#h3">h3</a></code>, <code><a
    href="#h4">h4</a></code>, <code><a href="#h5">h5</a></code>, <code><a
    href="#h6">h6</a></code>, <code><a href="#header">header</a></code>, or
    <code><a href="#footer">footer</a></code> elements as descendants, and
    with no <a href="#sectioning" title="sectioning elements">sectioning
    elements</a> as descendants; or, <a href="#inline-level0">inline-level
    content</a> (but not both).

   <dt>Element-specific attributes:

   <dd>None.

   <dt>DOM interface:

   <dd>No difference from <code><a
    href="#htmlelement">HTMLElement</a></code>.
  </dl>

  <p>The <code><a href="#footer">footer</a></code> element represents the
   footer for the section it <a href="#applyToSection">applies</a> to. A
   footer typically contains information about its section such as who wrote
   it, links to related documents, copyright data, and the like.

  <p><code><a href="#footer">footer</a></code> elements must not contain any
   <code><a href="#footer">footer</a></code>, <code><a
   href="#header">header</a></code>, <code><a href="#h1">h1</a></code>,
   <code><a href="#h2">h2</a></code>, <code><a href="#h3">h3</a></code>,
   <code><a href="#h4">h4</a></code>, <code><a href="#h5">h5</a></code>, or
   <code><a href="#h6">h6</a></code> elements, or any of the sectioning
   elements (such as <code><a href="#section">section</a></code>), as
   descendants.

  <p>When <a href="#determining0" title="Determining if a particular element
   contains block-level elements or inline-level content">used as an
   inline-level content</a> container, the element represents a <a
   href="#paragraph">paragraph</a>.

  <p>Contact information for the section given in a <code><a
   href="#footer">footer</a></code> should be marked up using the <code><a
   href="#address">address</a></code> element.</p>
  <!-- XXX examples needed -->

  <h4 id=the-address><span class=secno>3.8.10. </span>The <dfn
   id=address><code>address</code></dfn> element</h4>

  <p><a href="#block-level0" title="block-level elements">Block-level
   element</a>.

  <dl class=element>
   <dt>Contexts in which this element may be used:

   <dd>Where <a href="#block-level0">block-level elements</a> are expected.

   <dt>Content model:

   <dd><a href="#inline-level0">Inline-level content</a>.

   <dt>Element-specific attributes:

   <dd>None.

   <dt>DOM interface:

   <dd>No difference from <code><a
    href="#htmlelement">HTMLElement</a></code>.
  </dl>

  <p>The <code><a href="#address">address</a></code> element represents a <a
   href="#paragraph">paragraph</a> of contact information for the section it
   <a href="#applyToSection">applies</a> to.

  <div class=example>
   <p>For example, a page at the W3C Web site related to HTML might include
    the following contact information:</p>

   <pre>&lt;ADDRESS>
 &lt;A href="../People/Raggett/">Dave Raggett&lt;/A>, 
 &lt;A href="../People/Arnaud/">Arnaud Le Hors&lt;/A>, 
 contact persons for the &lt;A href="Activity">W3C HTML Activity&lt;/A>
&lt;/ADDRESS></pre>
  </div>

  <p>The <code><a href="#address">address</a></code> element must not be used
   to represent arbitrary addresses (e.g. postal addresses), unless those
   addresses are contact information for the section. (The <code><a
   href="#p">p</a></code> element is the appropriate element for marking up
   such addresses.)

  <p>The <code><a href="#address">address</a></code> element must not contain
   information other than contact information.

  <div class=example>
   <p>For example, the following is non-conforming use of the <code><a
    href="#address">address</a></code> element:</p>

   <pre>&lt;ADDRESS>Last Modified: 1999/12/24 23:37:50&lt;/ADDRESS></pre>
  </div>

  <p>Typically, the <code><a href="#address">address</a></code> element would
   be included with other information in a <code><a
   href="#footer">footer</a></code> element.

  <p>To determine the contact information for a sectioning element (such as a
   document's <code><a href="#body0">body</a></code> element, which would
   give the contact information for the page), UAs must collect all the
   <code><a href="#address">address</a></code> elements that <a
   href="#applyToSection">apply</a> to that sectioning element and its
   ancestor sectioning elements. The contact information is the collection of
   all the information given by those elements.

  <p class=note>Contact information for one sectioning element, e.g. a
   <code><a href="#aside">aside</a></code> element, does not apply to its
   ancestor elements, e.g. the page's <code><a href="#body0">body</a></code>.

  <h4 id=headings><span class=secno>3.8.11. </span><dfn id=headings0>Headings
   and sections</dfn></h4>

  <p>The <code><a href="#h1">h1</a></code>-<code><a href="#h6">h6</a></code>
   elements and the <code><a href="#header">header</a></code> element are
   headings.

  <p>The first heading in a sectioning element gives the header for that
   section. Subsequent headers of equal or higher <a href="#rank">rank</a>
   start new (implied) sections, headers of lower <a href="#rank">rank</a>
   start subsections that are part of the previous one.

  <p>Sectioning elements other than <code><a
   href="#blockquote">blockquote</a></code> are always considered subsections
   of their nearest ancestor sectioning element, regardless of what implied
   sections other headings may have created. However, <code><a
   href="#blockquote">blockquote</a></code> elements <em>are</em> associated
   with implied sections. Effectively, <code><a
   href="#blockquote">blockquote</a></code> elements act like sections on the
   inside, and act opaquely on the outside.

  <div class=example>
   <p>For the following fragment:</p>

   <pre>&lt;body&gt;
 &lt;h1&gt;Foo&lt;/h1&gt;
 &lt;h2&gt;Bar&lt;/h2&gt;
 &lt;blockquote&gt;
  &lt;h3&gt;Bla&lt;/h3&gt;
 &lt;/blockquote&gt;
 &lt;p&gt;Baz&lt;/p&gt;
 &lt;h2&gt;Quux&lt;/h2&gt;
 &lt;section&gt;
  &lt;h3&gt;Thud&lt;/h3&gt;
 &lt;/section&gt;
 &lt;p&gt;Grunt&lt;/p&gt;
&lt;/body&gt;</pre>

   <p>...the structure would be:</p>

   <ol>
    <li> Foo (heading of explicit <code><a href="#body0">body</a></code>
     section)
     <ol>
      <li> Bar (heading starting implied section)
       <ol>
        <li> Bla (heading of explicit <code><a
         href="#blockquote">blockquote</a></code> section)
       </ol>
       Baz (paragraph)

      <li> Quux (heading starting implied section)

      <li> Thud (heading of explicit <code><a
       href="#section">section</a></code> section)
     </ol>
     Grunt (paragraph)
   </ol>

   <p>Notice how the <code><a href="#blockquote">blockquote</a></code> nests
    inside an implicit section while the <code><a
    href="#section">section</a></code> does not (and in fact, ends the
    earlier implicit section so that a later paragraph is back at the top
    level).</p>
  </div>

  <p>Sections may contain headers of any <a href="#rank">rank</a>, but
   authors are strongly encouraged to either use only <code><a
   href="#h1">h1</a></code> elements, or to use elements of the appropriate
   <a href="#rank">rank</a> for the section's nesting level.

  <p>Authors are also encouraged to explictly wrap sections in sectioning
   elements, instead of relying on the implicit sections generated by having
   multiple heading in one sectioning element.

  <div class=example>
   <p>For example, the following is correct:</p>

   <pre>&lt;body&gt;
 &lt;h4&gt;Apples&lt;/h4&gt;
 &lt;p&gt;Apples are fruit.&lt;/p&gt;
 &lt;section&gt;
  &lt;h2&gt;Taste&lt;/h2&gt;
  &lt;p&gt;They taste lovely.&lt;/p&gt;
  &lt;h6&gt;Sweet&lt;/h6&gt;
  &lt;p&gt;Red apples are sweeter than green ones.&lt;/p&gt;
  &lt;h1&gt;Color&lt;/h1&gt;
  &lt;p&gt;Apples come in various colors.&lt;/p&gt;
 &lt;/section&gt;
&lt;/body&gt;</pre>

   <p>However, the same document would be more clearly expressed as:</p>

   <pre>&lt;body&gt;
 &lt;h1&gt;Apples&lt;/h1&gt;
 &lt;p&gt;Apples are fruit.&lt;/p&gt;
 &lt;section&gt;
  &lt;h2&gt;Taste&lt;/h2&gt;
  &lt;p&gt;They taste lovely.&lt;/p&gt;
  &lt;section&gt;
   &lt;h3&gt;Sweet&lt;/h3&gt;
   &lt;p&gt;Red apples are sweeter than green ones.&lt;/p&gt;
  &lt;/section&gt;
 &lt;/section&gt;
 &lt;section&gt;
  &lt;h2&gt;Color&lt;/h2&gt;
  &lt;p&gt;Apples come in various colors.&lt;/p&gt;
 &lt;/section&gt;
&lt;/body&gt;</pre>

   <p>Both of the documents above are semantically identical and would
    produce the same outline in compliant user agents.</p>
  </div>

  <h5 id=outlines><span class=secno>3.8.11.1. </span>Creating an outline</h5>

  <p>Documents can be viewed as a tree of sections, which defines how each
   element in the tree is semantically related to the others, in terms of the
   overall section structure. This tree is related to the document tree, but
   there is not a one-to-one relationship between elements in the DOM and the
   document's sections.

  <p>The tree of sections should be used when generating document outlines,
   for example when generating tables of contents.

  <p>To derive the tree of sections from the document tree, a hypothetical
   tree is used, consisting of a view of the document tree containing only
   the <code><a href="#h1">h1</a></code>-<code><a href="#h6">h6</a></code>
   and <code><a href="#header">header</a></code> elements, and the sectioning
   elements other than <code><a href="#blockquote">blockquote</a></code>.
   Descendants of <code><a href="#h1">h1</a></code>-<code><a
   href="#h6">h6</a></code>, <code><a href="#header">header</a></code>, and
   <code><a href="#blockquote">blockquote</a></code> elements must be removed
   from this view.

  <p>The hypothetical tree must be rooted at the <a href="#root-element">root
   element</a> or at a sectioning element. In particular, while the sections
   inside <code><a href="#blockquote">blockquote</a></code>s do not
   contribute to the document's tree of sections, <code><a
   href="#blockquote">blockquote</a></code>s can have outlines of their own.

  <p>UAs must take this hypothetical tree (which will become the outline) and
   mutate it by walking it depth first in <a href="#tree-order">tree
   order</a> and, for each <code><a href="#h1">h1</a></code>-<code><a
   href="#h6">h6</a></code> or <code><a href="#header">header</a></code>
   element that is not the first element of its parent sectioning element,
   inserting a new sectioning element, as follows:

  <dl class=switch>
   <dt>If the element is a <code><a href="#header">header</a></code> element,
    or if it is an <code><a href="#h1">h1</a></code>-<code><a
    href="#h6">h6</a></code> node of <a href="#rank">rank</a> equal to or
    higher than the first element in the parent sectioning element (assuming
    that is also an <code><a href="#h1">h1</a></code>-<code><a
    href="#h6">h6</a></code> node), or if the first element of the parent
    sectioning element is a sectioning element:

   <dd>Insert the new sectioning element as the immediately following sibling
    of the parent sectioning element, and move all the elements from the
    current heading element up to the end of the parent sectioning element
    into the new sectioning element.

   <dt>Otherwise:

   <dd>Move the current heading element, and all subsequent siblings up to
    but excluding the next sectioning element, <code><a
    href="#header">header</a></code> element, or <code><a
    href="#h1">h1</a></code>-<code><a href="#h6">h6</a></code> of equal or
    higher <a href="#rank">rank</a>, whichever comes first, into the new
    sectioning element, then insert the new sectioning element where the
    current header was.
  </dl>

  <p>The outline is then the resulting hypothetical tree. The <a href="#rank"
   title=rank>ranks</a> of the headers become irrelevant at this point: each
   sectioning element in the hypothetical tree contains either no or one
   heading element child. If there is one, then it gives the section's
   heading, of there isn't, the section has no heading.

  <p>Sections are nested as in the hypothetical tree. If a sectioning element
   is a child of another, that means it is a subsection of that other
   section.

  <p>When creating an interactive table of contents, entries should jump the
   user to the relevant section element, if it was a real element in the
   original document, or to the heading, if the section element was one of
   those created during the above process.

  <p class=example>Selecting the first section of the document therefore
   always takes the user to the top of the document, regardless of where the
   first header in the <code><a href="#body0">body</a></code> is to be found.</p>
  <!-- XXX assuming there is a body, anyway -->

  <div class=note>
   <p>The hypothetical tree (before mutations) could be generated by creating
    a <code>TreeWalker</code> with the following <a
    href="http://www.w3.org/TR/DOM-Level-2-Traversal-Range/traversal.html#Traversal-NodeFilter"><code>NodeFilter</code></a>
    (described here as an anonymous ECMAScript function). <a
    href="#refsDOMTR">[DOMTR]</a> <a href="#refsECMA262">[ECMA262]</a></p>

   <pre>function (n) {
  // This implementation only knows about HTML elements.
  // An implementation that supports other languages might be
  // different.

  // Reject anything that isn't an element.
  if (n.nodeType != Node.ELEMENT_NODE)
    return NodeFilter.FILTER_REJECT;

  // Skip any descendants of headings.
  if ((n.parentNode &amp;&amp; n.parentNode.namespaceURI == 'http://www.w3.org/1999/xhtml') &amp;&amp;
      (n.parentNode.localName == 'h1' || n.parentNode.localName == 'h2' ||
       n.parentNode.localName == 'h3' || n.parentNode.localName == 'h4' ||
       n.parentNode.localName == 'h5' || n.parentNode.localName == 'h6' ||
       n.parentNode.localName == 'header'))
    return NodeFilter.FILTER_REJECT;

  // Skip any blockquotes.
  if ((n.namespaceURI == 'http://www.w3.org/1999/xhtml') &amp;&amp;
      (n.localName == 'blockquote'))
    return NodeFilter.FILTER_REJECT;

  // Accept HTML elements in the list given in the prose above.
  if ((n.namespaceURI == 'http://www.w3.org/1999/xhtml') &amp;&amp;
      (n.localName == 'body' || /*n.localName == 'blockquote' ||*/
       n.localName == 'section' || n.localName == 'nav' ||
       n.localName == 'article' || n.localName == 'aside' ||
       n.localName == 'h1' || n.localName == 'h2' ||
       n.localName == 'h3' || n.localName == 'h4' ||
       n.localName == 'h5' || n.localName == 'h6' ||
       n.localName == 'header'))
    return NodeFilter.FILTER_ACCEPT;

  // Skip the rest.
  return NodeFilter.FILTER_SKIP;
}</pre>
  </div>

  <h5 id=associatedSection><span class=secno>3.8.11.2. </span>Determining
   which heading and section applies to a particular node</h5>

  <p>Given a particular node, user agents must use the following algorithm,
   <em>in the given order</em>, to determine which heading and section the
   node is most closely associated with. The processing of this algorithm
   must stop as soon as the associated section and heading are established
   (even if they are established to be nothing).

  <ol>
   <li>If the node has an ancestor that is a <code><a
    href="#header">header</a></code> element, then the associated heading is
    the most distant such ancestor. The associated section is that <code><a
    href="#header">header</a></code>'s associated section (i.e. repeat this
    algorithm for that <code><a href="#header">header</a></code>).

   <li>If the node has an ancestor that is an <code><a
    href="#h1">h1</a></code>-<code><a href="#h6">h6</a></code> element, then
    the associated heading is the most distant such ancestor. The associated
    section is that heading's section (i.e. repeat this algorithm for that
    heading element).

   <li>If the node is an <code><a href="#h1">h1</a></code>-<code><a
    href="#h6">h6</a></code> element or a <code><a
    href="#header">header</a></code> element, then the associated heading is
    the element itself. The UA must then generate the <a
    href="#outlines">hypothetical section tree</a> described in the previous
    section, rooted at the nearest section ancestor (or the <a
    href="#root-element">root element</a> if there is no such ancestor). If
    the parent of the heading in that hypothetical tree is an element in the
    real document tree, then that element is the associated section.
    Otherwise, there is no associated section element.

   <li>If the node is a sectioning element, then the associated section is
    itself. The UA must then generate the <a href="#outlines">hypothetical
    section tree</a> described in the previous section, rooted at the section
    itself. If the section element, in that hypothetical tree, has a child
    element that is an <code><a href="#h1">h1</a></code>-<code><a
    href="#h6">h6</a></code> element or a <code><a
    href="#header">header</a></code> element, then that element is the
    associated heading. Otherwise, there is no associated heading element.

   <li>If the node is a <code><a href="#footer">footer</a></code> or <code><a
    href="#address">address</a></code> element, then the associated section
    is the nearest ancestor sectioning element, if there is one. The node's
    associated heading is the same as that sectioning element's associated
    heading (i.e. repeat this algorithm for that sectioning element). If
    there is no ancestor sectioning element, the element has no associated
    section nor an associated heading.

   <li>Otherwise, the node is just a normal node, and the document has to be
    examined more closely to determine its section and heading. Create a view
    rooted at the nearest ancestor sectioning element (or the <a
    href="#root-element">root element</a> if there is none) that has just
    <code><a href="#h1">h1</a></code>-<code><a href="#h6">h6</a></code>
    elements, <code><a href="#header">header</a></code> elements, the node
    itself, and sectioning elements other than <code><a
    href="#blockquote">blockquote</a></code> elements. (Descendants of any of
    the nodes in this view can be ignored, as can any node later in the tree
    than the node in question, as the algorithm below merely walks backwards
    up this view.)

   <li>Let <var title="">n</var> be an iterator for this view, initialised at
    the node in question.

   <li>Let <var title="">c</var> be the current best candidate heading,
    initially null, and initially not used. It is used when top-level heading
    candidates are to be searched for (see below).

   <li>Repeat these steps (which effectively goes backwards through the
    node's previous siblings) until an answer is found:
    <ol>
     <li>If <var title="">n</var> points to a node with no previous sibling,
      and <var title="">c</var> is null, then return the node's parent node
      as the answer. If the node has no parent node, return null as the
      answer.

     <li>Otherwise, if <var title="">n</var> points to a node with no
      previous sibling, return <var title="">c</var> as the answer.

     <li>Adjust <var title="">n</var> so that it points to the previous
      sibling of the current position.

     <li>If <var title="">n</var> is pointing at an <code><a
      href="#h1">h1</a></code> or <code><a href="#header">header</a></code>
      element, then return that element as the answer.

     <li>If <var title="">n</var> is pointing at an <code><a
      href="#h2">h2</a></code>-<code><a href="#h6">h6</a></code> element, and
      heading candidates are not being searched for, then return that element
      as the answer.

     <li>Otherwise, if <var title="">n</var> is pointing at an <code><a
      href="#h2">h2</a></code>-<code><a href="#h6">h6</a></code> element, and
      either <var title="">c</var> is still null, or <var title="">c</var> is
      a heading of lower <a href="#rank">rank</a> than this one, then set
      <var title="">c</var> to be this element, and continue going backwards
      through the previous siblings.

     <li>If <var title="">n</var> is pointing at a sectioning element, then
      from this point on top-level heading candidates are being searched for.
      (Specifically, we are looking for the nearest top-level header for the
      current section.) Continue going backwards through the previous
      siblings.
    </ol>

   <li>If the answer from the previous step (the loop) is null, which can
    only happen if the node has no preceeding headings and is not contained
    in a sectioning element, then there is no associated heading and no
    associated section.

   <li>Otherwise, if the answer from the earlier loop step is a sectioning
    element, then the associated section is that element and the associated
    heading is that sectioning element's associated heading (i.e. repeat this
    algorithm for that section).

   <li>Otherwise, if the answer from that same earlier step is an <code><a
    href="#h1">h1</a></code>-<code><a href="#h6">h6</a></code> element or a
    <code><a href="#header">header</a></code> element, then the associated
    heading is that element and the associated section is that heading
    element's associated section (i.e. repeat this algorithm for that
    heading).
  </ol>

  <p class=note>Not all nodes have an associated header or section. For
   example, if a section is implied, as when multiple headers are found in
   one sectioning element, then a node in that section has an anonymous
   associated section (its section is not represented by a real element), and
   the algorithm above does not associate that node with any particular
   sectioning element.

  <div class=example>
   <p>For the following fragment:</p>

   <pre>&lt;body&gt;
 &lt;h1&gt;X&lt;/h1&gt;
 &lt;h2&gt;X&lt;/h2&gt;
 &lt;blockquote&gt;
  &lt;h3&gt;X&lt;/h3&gt;
 &lt;/blockquote&gt;
 &lt;p id="a"&gt;X&lt;/p&gt;
 &lt;h4&gt;Text Node A&lt;/h4&gt;
 &lt;section&gt;
  &lt;h5&gt;X&lt;/h5&gt;
 &lt;/section&gt;
 &lt;p&gt;Text Node B&lt;/p&gt;
&lt;/body&gt;</pre>

   <p>The associations are as follows (not all associations are shown):</p>

   <table>
    <thead>
     <tr>
      <th>Node

      <th>Associated heading

      <th>Associated section

    <tbody>
     <tr>
      <td><code>&lt;body&gt;</code>

      <td><code>&lt;h1&gt;</code>

      <td><code>&lt;body&gt;</code>

     <tr>
      <td><code>&lt;h1&gt;</code>

      <td><code>&lt;h1&gt;</code>

      <td><code>&lt;body&gt;</code>

     <tr>
      <td><code>&lt;h2&gt;</code>

      <td><code>&lt;h2&gt;</code>

      <td>None.

     <tr>
      <td><code>&lt;blockquote&gt;</code>

      <td><code>&lt;h2&gt;</code>

      <td>None.

     <tr>
      <td><code>&lt;h3&gt;</code>

      <td><code>&lt;h3&gt;</code>

      <td><code>&lt;blockquote&gt;</code>

     <tr>
      <td><code>&lt;p id="a"&gt;</code>

      <td><code>&lt;h2&gt;</code>

      <td>None.

     <tr>
      <td><code>Text Node A</code>

      <td><code>&lt;h4&gt;</code>

      <td>None.

     <tr>
      <td><code>Text Node B</code>

      <td><code>&lt;h1&gt;</code>

      <td><code>&lt;body&gt;</code>
   </table>
  </div>

  <h5 id=distinguishing><span class=secno>3.8.11.3. </span>Distinguishing
   site-wide headers from page headers</h5>

  <p>Given the <a href="#outlines">hypothetical section tree</a>, but
   ignoring any sections created for <code><a href="#nav">nav</a></code> and
   <code><a href="#aside">aside</a></code> elements, and any of their
   descendants, if the root of the tree is <a href="#the-body0">the
   <code>body</code> element</a>'s section, and it has only a single
   subsection which is created by an <code><a
   href="#article">article</a></code> element, then the header of <a
   href="#the-body0">the <code>body</code> element</a> should be assumed to
   be a site-wide header, and the header of the <code><a
   href="#article">article</a></code> element should be assumed to be the
   page's header.

  <p>If a page starts with a heading that is common to the whole site, the
   document must be authored such that, in the document's <a
   href="#outlines">hypothetical section tree</a>, ignoring any sections
   created for <code><a href="#nav">nav</a></code> and <code><a
   href="#aside">aside</a></code> elements and any of their descendants, the
   root of the tree is <a href="#the-body0">the <code>body</code>
   element</a>'s section, its heading is the site-wide heading, <a
   href="#the-body0">the <code>body</code> element</a> has just one
   subsection, that subsection is created by an <code><a
   href="#article">article</a></code> element, and that <code><a
   href="#article">article</a></code>'s header is the page heading.

  <p>If a page does not contain a site-wide heading, then the page must be
   authored such that, in the document's <a href="#outlines">hypothetical
   section tree</a>, ignoring any sections created for <code><a
   href="#nav">nav</a></code> and <code><a href="#aside">aside</a></code>
   elements and any of their descendants, either <a href="#the-body0">the
   <code>body</code> element</a> has no subsections, or it has more than one
   subsection, or it has a single subsection but that subsection is not
   created by an <code><a href="#article">article</a></code> element.

  <p class=note>Conceptually, a site is thus a document with many articles
   &mdash; when those articles are split into many pages, the heading of the
   original single page becomes the heading of the site, repeated on every
   page.

  <h3 id=prose><span class=secno>3.9. </span>Prose</h3>

  <h4 id=the-p><span class=secno>3.9.1. </span>The <dfn
   id=p><code>p</code></dfn> element</h4>

  <p><a href="#block-level0" title="block-level elements">Block-level
   element</a>.

  <dl class=element>
   <dt>Contexts in which this element may be used:

   <dd>Where <a href="#block-level0">block-level elements</a> are expected.

   <dt>Content model:

   <dd><a href="#significant" title="significant inline
    content">Significant</a> <a href="#inline-level0">inline-level
    content</a>.

   <dt>Element-specific attributes:

   <dd>None.

   <dt>DOM interface:

   <dd>No difference from <code><a
    href="#htmlelement">HTMLElement</a></code>.
  </dl>

  <p>The <code><a href="#p">p</a></code> element represents a <a
   href="#paragraph">paragraph</a>.

  <p><code><a href="#p">p</a></code> elements can contain a mixture of <a
   href="#strictly">strictly inline-level content</a>, such as text, images,
   hyperlinks, etc, and <a href="#structured">structured inline-level
   elements</a>, such as lists, tables, and block quotes. <code><a
   href="#p">p</a></code> elements must not be <a href="#significant"
   title="significant inline content">empty</a>.

  <div class=example>
   <p>The following examples are conforming HTML fragments:</p>

   <pre>&lt;p&gt;The little kitten gently seated himself on a piece of
carpet. Later in his life, this would be referred to as the time the
cat sat on the mat.&lt;/p&gt;</pre>

   <pre>&lt;fieldset&gt;
 &lt;legend&gt;Personal information&lt;/legend&gt;
 &lt;p&gt;
   &lt;label&gt;Name: &lt;input name="n"&gt;&lt;/label&gt;
   &lt;label&gt;&lt;input name="anon" type="checkbox"&gt; Hide from other users&lt;/label&gt;
 &lt;/p&gt;
 &lt;p&gt;&lt;label&gt;Address: &lt;textarea name="a"&gt;&lt;/textarea&gt;&lt;/label&gt;&lt;/p&gt;
&lt;/fieldset&gt;</pre>

   <pre>&lt;p&gt;There was once an example from Femley,&lt;br&gt;
Whose markup was of dubious quality.&lt;br&gt;
The validator complained,&lt;br&gt;
So the author was pained,&lt;br&gt;
To move the error from the markup to the rhyming.&lt;/p&gt;</pre>
  </div>

  <p>The <code><a href="#p">p</a></code> element should not be used when a
   more specific element is more appropriate.

  <div class=example>
   <p>The following example is technically correct:</p>

   <pre>&lt;section&gt;
 &lt;!-- ... --&gt;
 &lt;p&gt;Last modified: 2001-04-23&lt;/p&gt;
 &lt;p&gt;Author: fred@example.com&lt;/p&gt;
&lt;/section&gt;</pre>

   <p>However, it would be better marked-up as:</p>

   <pre>&lt;section&gt;
 &lt;!-- ... --&gt;
 &lt;footer&gt;Last modified: 2001-04-23&lt;/footer&gt;
 &lt;address&gt;Author: fred@example.com&lt;/address&gt;
&lt;/section&gt;</pre>

   <p>Or:</p>

   <pre>&lt;section&gt;
 &lt;!-- ... --&gt;
 &lt;footer&gt;
  &lt;p&gt;Last modified: 2001-04-23&lt;/p&gt;
  &lt;address&gt;Author: fred@example.com&lt;/address&gt;
 &lt;/footer&gt;
&lt;/section&gt;</pre>
  </div>

  <h4 id=the-hr><span class=secno>3.9.2. </span>The <dfn
   id=hr><code>hr</code></dfn> element</h4>

  <p><a href="#block-level0" title="block-level elements">Block-level
   element</a>.

  <dl class=element>
   <dt>Contexts in which this element may be used:

   <dd>Where <a href="#block-level0">block-level elements</a> are expected.

   <dt>Content model:

   <dd>Empty.

   <dt>Element-specific attributes:

   <dd>None.

   <dt>DOM interface:

   <dd>No difference from <code><a
    href="#htmlelement">HTMLElement</a></code>.
  </dl>

  <p>The <code><a href="#hr">hr</a></code> element represents a <a
   href="#paragraph">paragraph</a>-level thematic break, e.g. a scene change
   in a story, or a transition to another topic within a section of a
   reference book.

  <h4 id=the-br><span class=secno>3.9.3. </span>The <dfn
   id=br><code>br</code></dfn> element</h4>

  <p><a href="#strictly">Strictly inline-level content</a>.

  <dl class=element>
   <dt>Contexts in which this element may be used:

   <dd>Where <a href="#strictly">strictly inline-level content</a> is
    allowed.

   <dt>Content model:

   <dd>Empty.

   <dt>Element-specific attributes:

   <dd>None.

   <dt>DOM interface:

   <dd>No difference from <code><a
    href="#htmlelement">HTMLElement</a></code>.
  </dl>

  <p>The <code><a href="#br">br</a></code> element represents a line break.

  <p><code><a href="#br">br</a></code> elements must be empty. Any content
   inside <code><a href="#br">br</a></code> elements must not be considered
   part of the surrounding text.

  <p><code><a href="#br">br</a></code> elements must only be used for line
   breaks that are actually part of the content, as in poems or addresses.

  <div class=example>
   <p>The following example is correct usage of the <code><a
    href="#br">br</a></code> element:</p>

   <pre>&lt;p&gt;P. Sherman&lt;br&gt;
42 Wallaby Way&lt;br&gt;
Sydney&lt;/p&gt;</pre>
  </div>

  <p><code><a href="#br">br</a></code> elements must not be used for
   separating thematic groups in a paragraph.

  <div class=example>
   <p>The following examples are non-conforming, as they abuse the <code><a
    href="#br">br</a></code> element:</p>

   <pre>&lt;p&gt;&lt;a ...&gt;34 comments.&lt;/a&gt;&lt;br&gt;
&lt;a ...&gt;Add a comment.&lt;a&gt;&lt;/p&gt;</pre>

   <pre>&lt;p&gt;Name: &lt;input name="name"&gt;&lt;br&gt;
Address: &lt;input name="address"&gt;&lt;/p&gt;</pre>

   <p>Here are alternatives to the above, which are correct:</p>

   <pre>&lt;p&gt;&lt;a ...&gt;34 comments.&lt;/a&gt;&lt;/p&gt;
&lt;p&gt;&lt;a ...&gt;Add a comment.&lt;a&gt;&lt;/p&gt;</pre>

   <pre>&lt;p&gt;Name: &lt;input name="name"&gt;&lt;/p&gt;
&lt;p&gt;Address: &lt;input name="address"&gt;&lt;/p&gt;</pre>
   <!-- XXX should have labels in the examples above --></div>

  <h4 id=the-dialog><span class=secno>3.9.4. </span>The <dfn
   id=dialog><code>dialog</code></dfn> element</h4>

  <p><a href="#block-level0" title="block-level elements">Block-level
   element</a>.

  <dl class=element>
   <dt>Contexts in which this element may be used:

   <dd>Where <a href="#block-level0">block-level elements</a> are expected.

   <dt>Content model:

   <dd>Zero or more pairs of <code><a href="#dt">dt</a></code> and <code><a
    href="#dd">dd</a></code> elements.

   <dt>Element-specific attributes:

   <dd>None.

   <dt>DOM interface:

   <dd>No difference from <code><a
    href="#htmlelement">HTMLElement</a></code>.
  </dl>

  <p>The <code><a href="#dialog">dialog</a></code> element represents a
   conversation.

  <p>Each part of the conversation must have an explicit talker (or speaker)
   given by a <code><a href="#dt">dt</a></code> element, and a discourse (or
   quote) given by a <code><a href="#dd">dd</a></code> element.

  <div class=example>
   <p>This example demonstrates this using an extract from Abbot and
    Costello's famous sketch, <cite>Who's on first</cite>:</p>

   <pre>&lt;dialog>
 &lt;dt>Costello
 &lt;dd> Look, you gotta first baseman?
 &lt;dt> Abbott
 &lt;dd> Certainly.
 &lt;dt> Costello
 &lt;dd> Who's playing first?
 &lt;dt> Abbott
 &lt;dd> That's right.
 &lt;dt> Costello
 &lt;dd> When you pay off the first baseman every month, who gets the money?
 &lt;dt> Abbott
 &lt;dd> Every dollar of it. 
&lt;/dialog></pre>
  </div>

  <p class=note>Text in a <code><a href="#dt">dt</a></code> element in a
   <code><a href="#dialog">dialog</a></code> element is implicitly the source
   of the text given in the following <code><a href="#dd">dd</a></code>
   element, and the contents of the <code><a href="#dd">dd</a></code> element
   are implicitly a quote from that speaker. There is thus no need to include
   <code><a href="#cite2">cite</a></code>, <code><a href="#q">q</a></code>,
   or <code><a href="#blockquote">blockquote</a></code> elements in this
   markup. Indeed, a <code><a href="#q">q</a></code> element inside a
   <code><a href="#dd">dd</a></code> element in a conversation would actually
   imply the person talking were themselves quoting someone else. See the
   <code><a href="#cite2">cite</a></code>, <code><a href="#q">q</a></code>,
   and <code><a href="#blockquote">blockquote</a></code> elements for other
   ways to cite or quote.

  <h3 id=preformatted><span class=secno>3.10. </span>Preformatted text</h3>

  <h4 id=the-pre><span class=secno>3.10.1. </span>The <dfn
   id=pre><code>pre</code></dfn> element</h4>

  <p><a href="#block-level0" title="block-level elements">Block-level
   element</a>, and <a href="#structured" title="structured inline-level
   elements">structured inline-level element</a>.

  <dl class=element>
   <dt>Contexts in which this element may be used:

   <dd>Where <a href="#block-level0">block-level elements</a> are expected.

   <dd>Where <a href="#structured">structured inline-level elements</a> are
    allowed.

   <dt>Content model:

   <dd><a href="#strictly">Strictly inline-level content</a>.

   <dt>Element-specific attributes:

   <dd>None.

   <dt>DOM interface:

   <dd>No difference from <code><a
    href="#htmlelement">HTMLElement</a></code>.
  </dl>

  <p>The <code><a href="#pre">pre</a></code> element represents a block of
   preformatted text, in which structure is represented by typographic
   conventions rather than by elements.

  <p>Some examples of cases where the <code><a href="#pre">pre</a></code>
   element could be used:

  <ul>
   <li>Including an e-mail, with paragraphs indicated by blank lines, lists
    indicated by lines prefixed with a bullet, and so on.

   <li>Including fragments of computer code, with structure indicated
    according to the conventions of that language.

   <li>Displaying ASCII art.</li>
   <!-- XXX need a note about non-visual UAs -->
  </ul>

  <p>If, ignoring <a href="#text-node" title="text node">text nodes</a>
   consisting only of <a href="#inter-element" title="inter-element
   whitespace">whitespace</a>, the only child of a <code><a
   href="#pre">pre</a></code> is a <code><a href="#code">code</a></code>
   element, then the <code><a href="#pre">pre</a></code> element represents a
   block of computer code.

  <p>If, ignoring <a href="#text-node" title="text node">text nodes</a>
   consisting only of <a href="#inter-element" title="inter-element
   whitespace">whitespace</a>, the only child of a <code><a
   href="#pre">pre</a></code> is a <code><a href="#samp">samp</a></code>
   element, then the <code><a href="#pre">pre</a></code> element represents a
   block of computer output.</p>
  <!-- XXX examples -->

  <h3 id=lists0><span class=secno>3.11. </span>Lists</h3>

  <h4 id=the-ol><span class=secno>3.11.1. </span>The <dfn
   id=ol><code>ol</code></dfn> element</h4>

  <p><a href="#block-level0" title="block-level elements">Block-level
   element</a>, and <a href="#structured" title="structured inline-level
   elements">structured inline-level element</a>.

  <dl class=element>
   <dt>Contexts in which this element may be used:

   <dd>Where <a href="#block-level0">block-level elements</a> are expected.

   <dd>Where <a href="#structured">structured inline-level elements</a> are
    allowed.

   <dt>Content model:

   <dd>Zero or more <code><a href="#li">li</a></code> elements.

   <dt>Element-specific attributes:

   <dd><code title=attr-ol-start><a href="#start0">start</a></code>

   <dt>DOM interface:

   <dd>
    <pre
     class=idl>interface <dfn id=htmlolistelement>HTMLOListElement</dfn> : <a href="#htmlelement">HTMLElement</a> {
           attribute long <a href="#start1" title=dom-ol-start>start</a>;
};</pre>
  </dl>

  <p>The <code><a href="#ol">ol</a></code> element represents an ordered list
   of items (which are represented by <code><a href="#li">li</a></code>
   elements).

  <p>The <dfn id=start0 title=attr-ol-start><code>start</code></dfn>
   attribute, if present, must be a <a href="#valid0">valid integer</a>
   giving the ordinal value of the first list item.

  <p>If the <code title=attr-ol-start><a href="#start0">start</a></code>
   attribute is present, user agents must <a href="#rules0" title="rules for
   parsing integers">parse it as an integer</a>, in order to determine the
   attribute's value. The default value, used if the attribute is missing or
   if the value cannot be converted to a number according to the referenced
   algorithm, is 1.

  <p>The items of the list are the <code><a href="#li">li</a></code> element
   child nodes of the <code><a href="#ol">ol</a></code> element, in <a
   href="#tree-order">tree order</a>.

  <p>The first item in the list has the ordinal value given by the <code><a
   href="#ol">ol</a></code> element's <code title=attr-ol-start><a
   href="#start0">start</a></code> attribute, unless that <code><a
   href="#li">li</a></code> element has a <code title=attr-li-value><a
   href="#value">value</a></code> attribute with a value that can be
   successfully parsed, in which case it has the ordinal value given by that
   <code title=attr-li-value><a href="#value">value</a></code> attribute.

  <p>Each subsequent item in the list has the ordinal value given by its
   <code title=attr-li-value><a href="#value">value</a></code> attribute, if
   it has one, or, if it doesn't, the ordinal value of the previous item,
   plus one.

  <p>The <dfn id=start1 title=dom-ol-start><code>start</code></dfn> DOM
   attribute must <a href="#reflect">reflect</a> the value of the <code
   title=attr-ol-start><a href="#start0">start</a></code> content attribute.</p>
  <!-- XXX resuming numbering of lists from previous lists? -->
  <!-- XXX counting up and down? -->
  <!-- XXX reverse-counted lists? -->

  <h4 id=the-ul><span class=secno>3.11.2. </span>The <dfn
   id=ul><code>ul</code></dfn> element</h4>

  <p><a href="#block-level0" title="block-level elements">Block-level
   element</a>, and <a href="#structured" title="structured inline-level
   elements">structured inline-level element</a>.

  <dl class=element>
   <dt>Contexts in which this element may be used:

   <dd>Where <a href="#block-level0">block-level elements</a> are expected.

   <dd>Where <a href="#structured">structured inline-level elements</a> are
    allowed.

   <dt>Content model:

   <dd>Zero or more <code><a href="#li">li</a></code> elements.

   <dt>Element-specific attributes:

   <dd>None.

   <dt>DOM interface:

   <dd>No difference from <code><a
    href="#htmlelement">HTMLElement</a></code>.
  </dl>

  <p>The <code><a href="#ul">ul</a></code> element represents an unordered
   list of items (which are represented by <code><a href="#li">li</a></code>
   elements).

  <p>The items of the list are the <code><a href="#li">li</a></code> element
   child nodes of the <code><a href="#ul">ul</a></code> element.

  <h4 id=the-li><span class=secno>3.11.3. </span>The <dfn
   id=li><code>li</code></dfn> element</h4>

  <dl class=element>
   <dt>Contexts in which this element may be used:

   <dd>Inside <code><a href="#ol">ol</a></code> elements.

   <dd>Inside <code><a href="#ul">ul</a></code> elements.

   <dd>Inside <code><a href="#menu">menu</a></code> elements.

   <dt>Content model:

   <dd>When the element is a child of an <code><a href="#ol">ol</a></code> or
    <code><a href="#ul">ul</a></code> element and the grandchild of an
    element that is <a href="#determining0" title="Determining if a
    particular element contains block-level elements or inline-level
    content">being used as an inline-level content container</a>, or, when
    the element is a child of a <code><a href="#menu">menu</a></code>
    element: <a href="#inline-level0">inline-level content</a>.

   <dd>Otherwise: zero or more <a href="#block-level0">block-level
    elements</a>, or <a href="#inline-level0">inline-level content</a> (but
    not both).

   <dt>Element-specific attributes:

   <dd>If the element is a child of an <code><a href="#ol">ol</a></code>
    element: <code title=attr-li-value><a href="#value">value</a></code>

   <dd>If the element is not the child of an <code><a
    href="#ol">ol</a></code> element: None.

   <dt>DOM interface:

   <dd>
    <pre
     class=idl>interface <dfn id=htmllielement>HTMLLIElement</dfn> : <a href="#htmlelement">HTMLElement</a> {
           attribute long <a href="#value0" title=dom-li-value>value</a>;
};</pre>
  </dl>

  <p>The <code><a href="#li">li</a></code> element represents a list item. If
   its parent element is an <code><a href="#ol">ol</a></code>, <code><a
   href="#ul">ul</a></code>, or <code><a href="#menu">menu</a></code>
   element, then the element is an item of the parent element's list, as
   defined for those elements. Otherwise, the list item has no defined
   list-related relationship to any other <code><a href="#li">li</a></code>
   element.

  <p>When the list item is the child of an <code><a href="#ol">ol</a></code>
   or <code><a href="#ul">ul</a></code> element, the content model of the
   item depends on the way that parent element was used. If it was used as
   structured inline content (i.e. if <em>that</em> element's parent was <a
   href="#determining0" title="Determining if a particular element contains
   block-level elements or inline-level content">used as an inline-level
   content</a> container), then the <code><a href="#li">li</a></code> element
   must only contain <a href="#inline-level0">inline-level content</a>.
   Otherwise, the element may be used either for <a href="#inline-level0"
   title="inline-level content">inline content</a> or <a
   href="#block-level0">block-level elements</a>.

  <p>When the list item is the child of a <code><a
   href="#menu">menu</a></code> element, the <code><a
   href="#li">li</a></code> element must contain only <a
   href="#inline-level0">inline-level content</a>.

  <p>When the list item is not the child of an <code><a
   href="#ol">ol</a></code>, <code><a href="#ul">ul</a></code>, or <code><a
   href="#menu">menu</a></code> element, e.g. because it is an orphaned node
   not in the document, it may contain either for <a href="#inline-level0"
   title="inline-level content">inline content</a> or <a
   href="#block-level0">block-level elements</a>.

  <p>When <a href="#determining0" title="Determining if a particular element
   contains block-level elements or inline-level content">used as an
   inline-level content</a> container, the list item represents a single <a
   href="#paragraph">paragraph</a>.

  <p>The <dfn id=value title=attr-li-value><code>value</code></dfn>
   attribute, if present, must be a <a href="#valid0">valid integer</a>
   giving the ordinal value of the first list item.

  <p>If the <code title=attr-li-value><a href="#value">value</a></code>
   attribute is present, user agents must <a href="#rules0" title="rules for
   parsing integers">parse it as an integer</a>, in order to determine the
   attribute's value. If the attribute's value cannot be converted to a
   number, it must be treated as if the attribute was absent. The attribute
   has no default value.

  <p>The <code title=attr-li-value><a href="#value">value</a></code>
   attribute is processed relative to the element's parent <code><a
   href="#ol">ol</a></code> element (q.v.), if there is one. If there is not,
   the attribute has no effect.

  <p>The <dfn id=value0 title=dom-li-value><code>value</code></dfn> DOM
   attribute must <a href="#reflect">reflect</a> the value of the <code
   title=dom-li-value><a href="#value0">value</a></code> content attribute.

  <h4 id=the-dl><span class=secno>3.11.4. </span>The <dfn
   id=dl><code>dl</code></dfn> element</h4>

  <p><a href="#block-level0" title="block-level elements">Block-level
   element</a>, and <a href="#structured" title="structured inline-level
   elements">structured inline-level element</a>.

  <dl class=element>
   <dt>Contexts in which this element may be used:

   <dd>Where <a href="#block-level0">block-level elements</a> are expected.

   <dd>Where <a href="#structured">structured inline-level elements</a> are
    allowed.

   <dt>Content model:

   <dd>Zero or more groups each consisting of one or more <code><a
    href="#dt">dt</a></code> elements followed by one or mode <code><a
    href="#dd">dd</a></code> elements.

   <dt>Element-specific attributes:

   <dd>None.

   <dt>DOM interface:

   <dd>No difference from <code><a
    href="#htmlelement">HTMLElement</a></code>.
  </dl>

  <p>The <code><a href="#dl">dl</a></code> element introduces an unordered
   association list consisting of zero or more name-value groups (a
   description list). Each group must consist of one or more names (<code><a
   href="#dt">dt</a></code> elements) followed by one or more values
   (<code><a href="#dd">dd</a></code> elements).

  <p>Name-value groups may be terms and definitions, metadata topics and
   values, or any other groups of name-value data.

  <div class=example>
   <p>The following are all conforming HTML fragments.</p>

   <p>In the following example, one entry ("Authors") is linked to two values
    ("John" and "Luke").</p>

   <pre>&lt;dl&gt;
 &lt;dt&gt; Authors
 &lt;dd&gt; John
 &lt;dd&gt; Luke
 &lt;dt&gt; Editor
 &lt;dd&gt; Frank
&lt;/dl&gt;</pre>

   <p>In the following example, one definition is linked to two terms.</p>

   <pre>&lt;dl&gt;
 &lt;dt lang="en-US"&gt; &lt;dfn>color&lt;/dfn> &lt;/dt&gt;
 &lt;dt lang="en-GB"&gt; &lt;dfn>colour&lt;/dfn> &lt;/dt&gt;
 &lt;dd&gt; A sensation which (in humans) derives from the ability of
 the fine structure of the eye to distinguish three differently
 filtered analyses of a view. &lt;/dd&gt;
&lt;/dl&gt;</pre>

   <p>The following example illustrates the use of the <code><a
    href="#dl">dl</a></code> element to mark up metadata of sorts. At the end
    of the example, one group has two metadata labels ("Authors" and
    "Editors") and two values ("Robert Rothman" and "Daniel Jackson").</p>

   <pre>&lt;dl&gt;
 &lt;dt&gt; Last modified time &lt;/dt&gt;
 &lt;dd&gt; 2004-12-23T23:33Z &lt;/dd&gt;
 &lt;dt&gt; Recommended update interval &lt;/dt&gt;
 &lt;dd&gt; 60s &lt;/dd&gt;
 &lt;dt&gt; Authors &lt;/dt&gt;
 &lt;dt&gt; Editors &lt;/dt&gt;
 &lt;dd&gt; Robert Rothman &lt;/dd&gt;
 &lt;dd&gt; Daniel Jackson &lt;/dd&gt;
&lt;/dl&gt;</pre>
  </div>

  <p>If a <code><a href="#dl">dl</a></code> element is empty, it contains no
   groups.

  <p>If a <code><a href="#dl">dl</a></code> element contains non-<a
   href="#inter-element" title="inter-element whitespace">whitespace</a> <a
   href="#text-node" title="text node">text nodes</a>, or elements other than
   <code><a href="#dt">dt</a></code> and <code><a href="#dd">dd</a></code>,
   then those elements or <a href="#text-node" title="text node">text
   nodes</a> do not form part of any groups in that <code><a
   href="#dl">dl</a></code>, and the document is non-conforming.

  <p>If a <code><a href="#dl">dl</a></code> element contains only <code><a
   href="#dt">dt</a></code> elements, then it consists of one group with
   names but no values, and the document is non-conforming.

  <p>If a <code><a href="#dl">dl</a></code> element contains only <code><a
   href="#dd">dd</a></code> elements, then it consists of one group with
   values but no names, and the document is non-conforming.

  <p class=note>The <code><a href="#dl">dl</a></code> element is
   inappropriate for marking up dialogue, since dialogue is ordered (each
   speaker/line pair comes after the next). For an example of how to mark up
   dialogue, see the <code><a href="#dialog">dialog</a></code> element.

  <h4 id=the-dt><span class=secno>3.11.5. </span>The <dfn
   id=dt><code>dt</code></dfn> element</h4>

  <dl class=element>
   <dt>Contexts in which this element may be used:

   <dd>Before <code><a href="#dd">dd</a></code> or <code><a
    href="#dt">dt</a></code> elements inside <code><a
    href="#dl">dl</a></code> elements.

   <dd>Before a <code><a href="#dd">dd</a></code> element inside a <code><a
    href="#dialog">dialog</a></code> element.

   <dt>Content model:

   <dd><a href="#strictly">Strictly inline-level content</a>.

   <dt>Element-specific attributes:

   <dd>None.

   <dt>DOM interface:

   <dd>No difference from <code><a
    href="#htmlelement">HTMLElement</a></code>.
  </dl>

  <p>The <code><a href="#dt">dt</a></code> element represents the term, or
   name, part of a term-description group in a description list (<code><a
   href="#dl">dl</a></code> element), and the talker, or speaker, part of a
   talker-discourse pair in a conversation (<code><a
   href="#dialog">dialog</a></code> element).

  <p class=note>The <code><a href="#dt">dt</a></code> element itself, when
   used in a <code><a href="#dl">dl</a></code> element, does not indicate
   that its contents are a term being defined, but this can be indicated
   using the <code><a href="#dfn">dfn</a></code> element.

  <h4 id=the-dd><span class=secno>3.11.6. </span>The <dfn
   id=dd><code>dd</code></dfn> element</h4>

  <dl class=element>
   <dt>Contexts in which this element may be used:

   <dd>After <code><a href="#dt">dt</a></code> or <code><a
    href="#dd">dd</a></code> elements inside <code><a
    href="#dl">dl</a></code> elements.

   <dd>After a <code><a href="#dt">dt</a></code> element inside a <code><a
    href="#dialog">dialog</a></code> element.

   <dt>Content model:

   <dd>When the element is a child of a <code><a href="#dl">dl</a></code>
    element and the grandchild of an element that is <a href="#determining0"
    title="Determining if a particular element contains block-level elements
    or inline-level content">being used as an inline-level content
    container</a>: <a href="#inline-level0">inline-level content</a>.

   <dd>Otherwise: zero or more <a href="#block-level0">block-level
    elements</a>, or <a href="#inline-level0">inline-level content</a> (but
    not both).

   <dt>Element-specific attributes:

   <dd>None.

   <dt>DOM interface:

   <dd>No difference from <code><a
    href="#htmlelement">HTMLElement</a></code>.
  </dl>

  <p>The <code><a href="#dd">dd</a></code> element represents the
   description, definition, or value, part of a term-description group in a
   description list (<code><a href="#dl">dl</a></code> element), and the
   discourse, or quote, part in a conversation (<code><a
   href="#dialog">dialog</a></code> element).

  <p>The content model of a <code><a href="#dd">dd</a></code> element depends
   on the way its parent element is being used. If the parent element is a
   <code><a href="#dl">dl</a></code> element that is being used as structured
   inline content (i.e. if the <code><a href="#dl">dl</a></code> element's
   parent element is being <a href="#determining0" title="Determining if a
   particular element contains block-level elements or inline-level
   content">used as an inline-level content</a> container), then the <code><a
   href="#dd">dd</a></code> element must only contain <a
   href="#inline-level0">inline-level content</a>.

  <p>Otherwise, the element may be used either for <a href="#inline-level0"
   title="inline-level content">inline content</a> or <a
   href="#block-level0">block-level elements</a>.

  <h3 id=phrase><span class=secno>3.12. </span>Phrase elements</h3>
  <!-- XXX ruby (delayed until someone can define it with error handling rules) -->

  <h4 id=the-a><span class=secno>3.12.1. </span>The <dfn
   id=a><code>a</code></dfn> element</h4>

  <p><a href="#interactive1" title="interactive elements">Interactive</a>, <a
   href="#strictly">strictly inline-level content</a>.

  <dl class=element>
   <dt>Contexts in which this element may be used:

   <dd>Where <a href="#strictly">strictly inline-level content</a> is
    allowed, if there are no ancestor <a href="#interactive1">interactive
    elements</a>.

   <dt>Content model:

   <dd>When used in an element whose content model is only <a
    href="#strictly">strictly inline-level content</a>: only <a
    href="#significant" title="significant inline content">significant</a> <a
    href="#strictly">strictly inline-level content</a>, but there must be no
    <a href="#interactive1" title="interactive elements">interactive</a>
    descendants.

   <dd>Otherwise: any <a href="#significant" title="significant inline
    content">significant</a> <a href="#inline-level0">inline-level
    content</a>, but there must be no <a href="#interactive1"
    title="interactive elements">interactive</a> descendants.

   <dt>Element-specific attributes:

   <dd><code title=attr-hyperlink-href><a href="#href6">href</a></code>

   <dd><code title=attr-hyperlink-target><a href="#target3">target</a></code>

   <dd><code title=attr-hyperlink-ping><a href="#ping">ping</a></code>

   <dd><code title=attr-hyperlink-rel><a href="#rel3">rel</a></code>

   <dd><code title=attr-hyperlink-media><a href="#media12">media</a></code>

   <dd><code title=attr-hyperlink-hreflang><a
    href="#hreflang3">hreflang</a></code>

   <dd><code title=attr-hyperlink-type><a href="#type17">type</a></code>

   <dt>DOM interface:

   <dd>
    <pre
     class=idl>interface <dfn id=htmlanchorelement>HTMLAnchorElement</dfn> : <a href="#htmlelement">HTMLElement</a> {
           attribute DOMString <a href="#href3" title=dom-a-href>href</a>;
           attribute DOMString <a href="#target1" title=dom-a-target>target</a>;
           attribute DOMString <a href="#ping0" title=dom-a-ping>ping</a>;
           attribute DOMString <a href="#rel1" title=dom-a-rel>rel</a>;
  readonly attribute DOMTokenList <a href="#rellist0" title=dom-a-relList>relList</a>;
           attribute DOMString <a href="#media4" title=dom-a-media>media</a>;
           attribute DOMString <a href="#hreflang1" title=dom-a-hreflang>hreflang</a>;
           attribute DOMString <a href="#type3" title=dom-a-type>type</a>;
};</pre>

    <p>The <code title=command-ro><a href="#command2">Command</a></code>
     interface must also be implemented by this element.</p>
  </dl>

  <p>If the <code><a href="#a">a</a></code> element has an <code
   title=attr-hyperlink-href><a href="#href6">href</a></code> attribute, then
   it represents a <a href="#hyperlinks">hyperlink</a>.

  <p>If the <code><a href="#a">a</a></code> element has no <code
   title=attr-hyperlink-href><a href="#href6">href</a></code> attribute, then
   the element is a placeholder for where a link might otherwise have been
   placed, if it had been relevant.

  <p>The <code title=attr-hyperlink-target><a
   href="#target3">target</a></code>, <code title=attr-hyperlink-ping><a
   href="#ping">ping</a></code>, <code title=attr-hyperlink-rel><a
   href="#rel3">rel</a></code>, <code title=attr-hyperlink-media><a
   href="#media12">media</a></code>, <code title=attr-hyperlink-hreflang><a
   href="#hreflang3">hreflang</a></code>, and <code
   title=attr-hyperlink-type><a href="#type17">type</a></code> attributes
   must be omitted if the <code title=attr-hyperlink-href><a
   href="#href6">href</a></code> attribute is not present.</p>
  <!-- XXX really? that makes it harder to use as a
  placeholder. -->

  <div class=example>
   <p>If a site uses a consistent navigation toolbar on every page, then the
    link that would normally link to the page itself could be marked up using
    an <code><a href="#a">a</a></code> element:</p>

   <pre>&lt;nav>
 &lt;ul>
  &lt;li> &lt;a href="/">Home&lt;/a> &lt;/li>
  &lt;li> &lt;a href="/news">News&lt;/a> &lt;/li>
  &lt;li> &lt;a>Examples&lt;/a> &lt;/li>
  &lt;li> &lt;a href="/legal">Legal&lt;/a> &lt;/li>
 &lt;/ul>
&lt;/nav></pre>
  </div>

  <p>Interactive user agents should allow users to <a href="#following0"
   title="following hyperlinks">follow hyperlinks</a> created using the
   <code><a href="#a">a</a></code> element. The <code
   title=attr-hyperlink-href><a href="#href6">href</a></code>, <code
   title=attr-hyperlink-target><a href="#target3">target</a></code> and <code
   title=attr-hyperlink-ping><a href="#ping">ping</a></code> attributes
   decide how the link is followed. The <code title=attr-hyperlink-rel><a
   href="#rel3">rel</a></code>, <code title=attr-hyperlink-media><a
   href="#media12">media</a></code>, <code title=attr-hyperlink-hreflang><a
   href="#hreflang3">hreflang</a></code>, and <code
   title=attr-hyperlink-type><a href="#type17">type</a></code> attributes may
   be used to indicate to the user the likely nature of the target resource
   before the user follows the link.

  <p>The <a href="#activation0">activation behavior</a> of <code><a
   href="#a">a</a></code> elements that represent <span>hyperlinks</span> is
   to run the following steps:

  <ol>
   <li>
    <p>If the <code title=event-DOMActivate>DOMActivate</code> event in
     question is not <span title=concept-events-trusted>trusted</span> (i.e.
     a <code title=dom-click><a href="#click">click()</a></code> method call
     was the reason for the event being dispatched), and the <code><a
     href="#a">a</a></code> element's <code title=attr-hyperlink-target><a
     href="#target3">target</a></code> attribute is <span
     class=big-issue>...</span> then raise an <code>INVALID_ACCESS_ERR</code>
     exception and abort these steps.

   <li>
    <p>If the target of the <code title=event-DOMActivate>DOMActivate</code>
     event is an <code><a href="#img">img</a></code> element with an <code
     title=attr-img-ismap><a href="#ismap">ismap</a></code> attribute
     specified, then server-side image map processing must be performed, as
     follows:</p>

    <ol><!-- http://software.hixie.ch/utilities/js/live-dom-viewer/?%3C%21DOCTYPE%20html%3E%0A...%3Ca%20href%3D%22%23%22%3E%3Cimg%20ismap%20usemap%3D%22%23a%22%20src%3D/resources/images/smallcats%3E%3C/a%3E%0A%3Cmap%20name%3Da%3E%3Carea%20shape%3Drect%20coords%3D0%2C0%2C50%2C50%20href%3Db%3E%3C/map%3E -->

     <li>If the <code title=event-DOMActivate>DOMActivate</code> event was
      dispatched as the result of a real pointing-device-triggered <code
      title=event-click>click</code> event on the <code><a
      href="#img">img</a></code> element, then let <var title="">x</var> be
      the distance in CSS pixels from the left edge of the image to the
      location of the click, and let <var title="">y</var> be the distance in
      CSS pixels from the top edge of the image to the location of the click.
      Otherwise, let <var title="">x</var> and <var title="">y</var> be zero.

     <li>Let the <dfn id=hyperlink2><var>hyperlink suffix</var></dfn> be a
      U+003F QUESTION MARK character, the value of <var title="">x</var>
      expressed as a base-ten integer using ASCII digits (U+0030 DIGIT ZERO
      to U+0039 DIGIT NINE), a U+002C COMMA character, and the value of <var
      title="">y</var> expressed as a base-ten integer using ASCII digits.
    </ol>

   <li>
    <p>Finally, the user agent must <a href="#following0" title="following
     hyperlinks">follow the hyperlink</a> defined by the <code><a
     href="#a">a</a></code> element. If the steps above defined a <var><a
     href="#hyperlink2">hyperlink suffix</a></var>, then take that into
     account when following the hyperlink.
  </ol>

  <p class=note>One way that a user agent can enable users to follow
   hyperlinks is by allowing <code><a href="#a">a</a></code> elements to be
   clicked, or focussed and activated by the keyboard. This <a
   href="#interactive1" title="interactive elements">will cause</a> the
   aforementioned <a href="#activation0">activation behavior</a> to be
   invoked.

  <p>The <code><a href="#a">a</a></code> element must not be <a
   href="#significant" title="significant inline content">empty</a>.

  <p>The DOM attributes <dfn id=href3
   title=dom-a-href><code>href</code></dfn>, <dfn id=ping0
   title=dom-a-ping><code>ping</code></dfn>, <dfn id=target1
   title=dom-a-target><code>target</code></dfn>, <dfn id=rel1
   title=dom-a-rel><code>rel</code></dfn>, <dfn id=media4
   title=dom-a-media><code>media</code></dfn>, <dfn id=hreflang1
   title=dom-a-hreflang><code>hreflang</code></dfn>, and <dfn id=type3
   title=dom-a-type><code>type</code></dfn>, must each <a
   href="#reflect">reflect</a> the respective content attributes of the same
   name.

  <p>The DOM attribute <dfn id=rellist0
   title=dom-a-rellist><code>relList</code></dfn> must <a
   href="#reflect">reflect</a> the <code title=attr-hyperlink-rel><a
   href="#rel3">rel</a></code> content attribute.

  <h4 id=the-q><span class=secno>3.12.2. </span>The <dfn
   id=q><code>q</code></dfn> element</h4>

  <p><a href="#strictly">Strictly inline-level content</a>.

  <dl class=element>
   <dt>Contexts in which this element may be used:

   <dd>Where <a href="#strictly">strictly inline-level content</a> is
    allowed.

   <dt>Content model:

   <dd>When used in an element whose content model is only <a
    href="#strictly">strictly inline-level content</a>: only <a
    href="#strictly">strictly inline-level content</a>.

   <dd>Otherwise: any <a href="#inline-level0">inline-level content</a>.

   <dt>Element-specific attributes:

   <dd><code title=attr-q-cite><a href="#cite1">cite</a></code>

   <dt>DOM interface:

   <dd> The <code><a href="#q">q</a></code> element uses the <code><a
    href="#htmlquoteelement">HTMLQuoteElement</a></code> interface.
  </dl>

  <p>The <code><a href="#q">q</a></code> element represents a part of a
   paragraph quoted from another source.

  <p>Content inside a <code><a href="#q">q</a></code> element must be quoted
   from another source, whose URI, if it has one, should be cited in the <dfn
   id=cite1 title=attr-q-cite><code>cite</code></dfn> attribute.

  <p>If the <code title=attr-q-cite><a href="#cite1">cite</a></code>
   attribute is present, it must be a URI (or IRI). User agents should allow
   users to follow such citation links.

  <p>If a <code><a href="#q">q</a></code> element is contained (directly or
   indirectly) in a <a href="#paragraph">paragraph</a> that contains a single
   <code><a href="#cite2">cite</a></code> element and has no other <code><a
   href="#q">q</a></code> element descendants, then, the citation given by
   that <code><a href="#cite2">cite</a></code> element gives the source of
   the quotation contained in the <code><a href="#q">q</a></code> element.</p>
  <!-- XXX need examples -->

  <h4 id=the-cite><span class=secno>3.12.3. </span>The <dfn
   id=cite2><code>cite</code></dfn> element</h4>

  <p><a href="#strictly">Strictly inline-level content</a>.

  <dl class=element>
   <dt>Contexts in which this element may be used:

   <dd>Where <a href="#strictly">strictly inline-level content</a> is
    allowed.

   <dt>Content model:

   <dd><a href="#strictly">Strictly inline-level content</a>.

   <dt>Element-specific attributes:

   <dd>None.

   <dt>DOM interface:

   <dd>No difference from <code><a
    href="#htmlelement">HTMLElement</a></code>.</dd>
   <!-- XXX should the cite element have a cite attribute? -->
  </dl>

  <p>The <code><a href="#cite2">cite</a></code> element represents a
   citation: the source, or reference, for a quote or statement made in the
   document.

  <p class=note>A <em>citation</em> is not a <em>quote</em> (for which the
   <code><a href="#q">q</a></code> element is appropriate).

  <div class=example>
   <p>This is incorrect usage:</p>

   <pre>&lt;p>&lt;cite>This is wrong!&lt;/cite>, said Ian.&lt;/p></pre>

   <p>This is the correct way to do it:</p>

   <pre>&lt;p>&lt;q>This is correct!&lt;/q>, said &lt;cite>Ian&lt;/cite>.&lt;/p></pre>

   <p>This is also wrong, because the title and the name are not references
    or citations:</p>

   <pre>&lt;p>My favourite book is &lt;cite>The Reality Dysfunction&lt;/cite>
by &lt;cite>Peter F. Hamilton&lt;/cite>.&lt;/p></pre>

   <p>This is correct, because even though the source is not quoted, it is
    cited:</p>

   <pre>&lt;p>According to &lt;cite>the Wikipedia article on
HTML&lt;/cite>, HTML is defined in formal specifications that were
developed and published throughout the 1990s.&lt;/p></pre>
  </div>

  <p class=note>The <code><a href="#cite2">cite</a></code> element can apply
   to <code><a href="#blockquote">blockquote</a></code> and <code><a
   href="#q">q</a></code> elements in certain cases described in the
   definitions of those elements.

  <h4 id=the-em><span class=secno>3.12.4. </span>The <dfn
   id=em><code>em</code></dfn> element</h4>

  <p><a href="#strictly">Strictly inline-level content</a>.

  <dl class=element>
   <dt>Contexts in which this element may be used:

   <dd>Where <a href="#strictly">strictly inline-level content</a> is
    allowed.

   <dt>Content model:

   <dd>When used in an element whose content model is only <a
    href="#strictly">strictly inline-level content</a>: only <a
    href="#strictly">strictly inline-level content</a>.

   <dd>Otherwise: any <a href="#inline-level0">inline-level content</a>.

   <dt>Element-specific attributes:

   <dd>None.

   <dt>DOM interface:

   <dd>No difference from <code><a
    href="#htmlelement">HTMLElement</a></code>.
  </dl>

  <p>The <code><a href="#em">em</a></code> element represents stress emphasis
   of its contents.

  <p>The level of emphasis that a particlar piece of content has is given by
   its number of ancestor <code><a href="#em">em</a></code> elements.

  <p>The placement of emphasis changes the meaning of the sentence. The
   element thus forms an integral part of the content. The precise way in
   which emphasis is used in this way depends on the language.

  <div class=example>
   <p>These examples show how changing the emphasis changes the meaning.
    First, a general statement of fact, with no emphasis:</p>

   <pre>&lt;p>Cats are cute animals.&lt;/p></pre>

   <p>By emphasising the first word, the statement implies that the kind of
    animal under discussion is in question (maybe someone is asserting that
    dogs are cute):</p>

   <pre>&lt;p>&lt;em>Cats&lt;/em> are cute animals.&lt;/p></pre>

   <p>Moving the emphasis to the verb, one highlights that the truth of the
    entire sentence is in question (maybe someone is saying cats are not
    cute):</p>

   <pre>&lt;p>Cats &lt;em>are&lt;/em> cute animals.&lt;/p></pre>

   <p>By moving it to the adjective, the exact nature of the cats is
    reasserted (maybe someone suggested cats were <em>mean</em> animals):</p>

   <pre>&lt;p>Cats are &lt;em>cute&lt;/em> animals.&lt;/p></pre>

   <p>Similarly, if someone asserted that cats were vegetables, someone
    correcting this might emphasise the last word:</p>

   <pre>&lt;p>Cats are cute &lt;em>animals&lt;/em>.&lt;/p></pre>

   <p>By emphasising the entire sentence, it becomes clear that the speaker
    is fighting hard to get the point across. This kind of emphasis also
    typically affects the punctuation, hence the exclamation mark here.</p>

   <pre>&lt;p>&lt;em>Cats are cute animals!&lt;/em>&lt;/p></pre>

   <p>Anger mixed with emphasising the cuteness could lead to markup such as:</p>

   <pre>&lt;p>&lt;em>Cats are &lt;em>cute&lt;/em> animals!&lt;/em>&lt;/p></pre>
  </div>
  <!-- XXX should say it is wrong to use as in:

   <p><em>Note</em>: ...</p>

  -->

  <h4 id=the-strong><span class=secno>3.12.5. </span>The <dfn
   id=strong><code>strong</code></dfn> element</h4>

  <p><a href="#strictly">Strictly inline-level content</a>.

  <dl class=element>
   <dt>Contexts in which this element may be used:

   <dd>Where <a href="#strictly">strictly inline-level content</a> is
    allowed.

   <dt>Content model:

   <dd>When used in an element whose content model is only <a
    href="#strictly">strictly inline-level content</a>: only <a
    href="#strictly">strictly inline-level content</a>.

   <dd>Otherwise: any <a href="#inline-level0">inline-level content</a>.

   <dt>Element-specific attributes:

   <dd>None.

   <dt>DOM interface:

   <dd>No difference from <code><a
    href="#htmlelement">HTMLElement</a></code>.
  </dl>

  <p>The <code><a href="#strong">strong</a></code> element represents strong
   importance for its contents.

  <p>The relative level of importance of a piece of content is given by its
   number of ancestor <code><a href="#strong">strong</a></code> elements;
   each <code><a href="#strong">strong</a></code> element increases the
   importance of its contents.

  <p>Changing the importance of a piece of text with the <code><a
   href="#strong">strong</a></code> element does not change the meaning of
   the sentence.

  <div class=example>
   <p>Here is an example of a warning notice in a game, with the various
    parts marked up according to how important they are:</p>
   <!-- DO NOT REFLOW THIS EXAMPLE it has been carefully balanced -->
   <pre>&lt;p>&lt;strong>Warning.&lt;/strong> This dungeon is dangerous.
&lt;strong>Avoid the ducks.&lt;/strong> Take any gold you find.
&lt;strong>&lt;strong>Do not take any of the diamonds&lt;/strong>,
they are explosive and &lt;strong>will destroy anything within
ten meters.&lt;/strong>&lt;/strong> You have been warned.&lt;/p></pre>
  </div>

  <h4 id=the-small><span class=secno>3.12.6. </span>The <dfn
   id=small><code>small</code></dfn> element</h4>

  <p><a href="#strictly">Strictly inline-level content</a>.

  <dl class=element>
   <dt>Contexts in which this element may be used:

   <dd>Where <a href="#strictly">strictly inline-level content</a> is
    allowed.

   <dt>Content model:

   <dd>When used in an element whose content model is only <a
    href="#strictly">strictly inline-level content</a>: only <a
    href="#strictly">strictly inline-level content</a>.

   <dd>Otherwise: any <a href="#inline-level0">inline-level content</a>.

   <dt>Element-specific attributes:

   <dd>None.

   <dt>DOM interface:

   <dd>No difference from <code><a
    href="#htmlelement">HTMLElement</a></code>.
  </dl>

  <p>The <code><a href="#small">small</a></code> element represents small
   print (part of a document often describing legal restrictions, such as
   copyrights or other disadvantages), or other side comments.

  <p class=note>The <code><a href="#small">small</a></code> element does not
   "de-emphasise" or lower the importance of text emphasised by the <code><a
   href="#em">em</a></code> element or marked as important with the <code><a
   href="#strong">strong</a></code> element.

  <div class=example>
   <p>In this example the footer contains contact information and a
    copyright.</p>

   <pre>&lt;footer>
 &lt;address>
  For more details, contact
  &lt;a href="mailto:js@example.com">John Smith&lt;/a>.
 &lt;/address>
 &lt;p>&lt;small>&copy; copyright 2038 Example Corp.&lt;/small>&lt;/p>
&lt;/footer></pre>

   <p>In this second example, the <code><a href="#small">small</a></code>
    element is used for a side comment.</p>

   <pre>&lt;p>Example Corp today announced record profits for the
second quarter &lt;small>(Full Disclosure: Foo News is a subsidiary of
Example Corp)&lt;/small>, leading to speculation about a third quarter
merger with Demo Group.&lt;/p></pre>

   <p>In this last example, the <code><a href="#small">small</a></code>
    element is marked as being <em>important</em> small print.</p>

   <pre>&lt;p>&lt;strong>&lt;small>Continued use of this service will result in a kiss.&lt;/small>&lt;/strong>&lt;/p></pre>
  </div>

  <h4 id=the-m><span class=secno>3.12.7. </span>The <dfn
   id=m><code>m</code></dfn> element</h4>

  <p><a href="#strictly">Strictly inline-level content</a>.

  <dl class=element>
   <dt>Contexts in which this element may be used:

   <dd>Where <a href="#strictly">strictly inline-level content</a> is
    allowed.

   <dt>Content model:

   <dd>When used in an element whose content model is only <a
    href="#strictly">strictly inline-level content</a>: only <a
    href="#strictly">strictly inline-level content</a>.

   <dd>Otherwise: any <a href="#inline-level0">inline-level content</a>.

   <dt>Element-specific attributes:

   <dd>None.

   <dt>DOM interface:

   <dd>No difference from <code><a
    href="#htmlelement">HTMLElement</a></code>.
  </dl>

  <p>The <code><a href="#m">m</a></code> element represents a run of text
   marked or highlighted.

  <div class=example>
   <p>In the following snippet, a paragraph of text refers to a specific part
    of a code fragment.</p>

   <pre>&lt;p>The highlighted part below is where the error lies:&lt;/p>
&lt;pre>&lt;code>var i: Integer;
begin
   i := &lt;m>1.1&lt;/m>;
end.&lt;/code>&lt;/pre></pre>

   <p>Another example of the <code><a href="#m">m</a></code> element is
    highlighting parts of a document that are matching some search string. If
    someone looked at a document, and the server knew that the user was
    searching for the word "kitten", then the server might return the
    document with one paragraph modified as follows:</p>

   <pre>&lt;p>I also have some &lt;m>kitten&lt;/m>s who are visiting me
these days. They're really cute. I think they like my garden!&lt;/p></pre>
  </div>

  <h4 id=the-dfn><span class=secno>3.12.8. </span>The <dfn
   id=dfn><code>dfn</code></dfn> element</h4>

  <p><a href="#strictly">Strictly inline-level content</a>.

  <dl class=element>
   <dt>Contexts in which this element may be used:

   <dd>Where <a href="#strictly">strictly inline-level content</a> is
    allowed, if there are no ancestor <code><a href="#dfn">dfn</a></code>
    elements.

   <dt>Content model:

   <dd><a href="#strictly">Strictly inline-level content</a>, but there must
    be no descendant <code><a href="#dfn">dfn</a></code> elements.

   <dt>Element-specific attributes:

   <dd>None, but the <code title=attr-dfn-title><a
    href="#title4">title</a></code> attribute has special semantics on this
    element.

   <dt>DOM interface:

   <dd>No difference from <code><a
    href="#htmlelement">HTMLElement</a></code>.
  </dl>

  <p>The <code><a href="#dfn">dfn</a></code> element represents the defining
   instance of a term. The <a href="#paragraph">paragraph</a>, <a href="#dl"
   title=dl>description list group</a>, or <a href="#sectioning"
   title="sectioning elements">section</a> that contains the <code><a
   href="#dfn">dfn</a></code> element contains the definition for the term
   given by the contents of the <code><a href="#dfn">dfn</a></code> element.

  <p><code><a href="#dfn">dfn</a></code> elements must not be nested.

  <p><dfn id=defining>Defining term</dfn>: If the <code><a
   href="#dfn">dfn</a></code> element has a <dfn id=title4
   title=attr-dfn-title><code>title</code></dfn> attribute, then the exact
   value of that attribute is the term being defined. Otherwise, if it
   contains exactly one element child node and no child <a href="#text-node"
   title="text node">text nodes</a>, and that child element is an <code><a
   href="#abbr">abbr</a></code> element with a <code title=attr-abbr-title><a
   href="#title5">title</a></code> attribute, then the exact value of
   <em>that</em> attribute is the term being defined. Otherwise, it is the
   exact <code><a href="#textcontent">textContent</a></code> of the <code><a
   href="#dfn">dfn</a></code> element that gives the term being defined.</p>
  <!-- XXX that means <dfn>x \n x</dfn> won't match <span>x x</span> -->

  <p>If the <code title=attr-dfn-title><a href="#title4">title</a></code>
   attribute of the <code><a href="#dfn">dfn</a></code> element is present,
   then it must only contain the term being defined.

  <p>There must only be one <code><a href="#dfn">dfn</a></code> element per
   document for each term defined (i.e. there must not be any duplicate <a
   href="#defining" title="defining term">terms</a>).

  <p class=note>The <code title=attr-title><a href="#title">title</a></code>
   attribute of ancestor elements does not affect <code><a
   href="#dfn">dfn</a></code> elements.

  <p>The <code><a href="#dfn">dfn</a></code> element enables automatic
   cross-references. Specifically, any <code><a href="#span">span</a></code>,
   <code><a href="#abbr">abbr</a></code>, <code><a
   href="#code">code</a></code>, <code><a href="#var">var</a></code>,
   <code><a href="#samp">samp</a></code>, or <code><a href="#i">i</a></code>
   element that has a non-empty <code title=attr-title><a
   href="#title">title</a></code> attribute whose value exactly equals the <a
   href="#defining" title="defining term">term</a> of a <code><a
   href="#dfn">dfn</a></code> element in the same document, or which has no
   <code title=attr-title><a href="#title">title</a></code> attribute but
   whose <code><a href="#textcontent">textContent</a></code> exactly equals
   the <a href="#defining" title="defining term">term</a> of a <code><a
   href="#dfn">dfn</a></code> element in the document, and that has no <a
   href="#interactive1">interactive elements</a> or <code><a
   href="#dfn">dfn</a></code> elements either as ancestors or descendants,
   and has no other elements as ancestors that are themselves matching these
   conditions, should be presented in such a way that the user can jump from
   the element to the first <code><a href="#dfn">dfn</a></code> element
   giving the defining instance of that term.</p>
  <!-- XXX that means <dfn>x x</dfn> won't match <span>x \n x</span> -->
  <!-- need to mention that <span> is useful for cross-refs that don't
  actually use the term itself -->

  <div class=example>
   <p>In the following fragment, the term "GDO" is first defined in the first
    paragraph, then used in the second. A compliant UA could provide a link
    from the <code><a href="#abbr">abbr</a></code> element in the second
    paragraph to the <code><a href="#dfn">dfn</a></code> element in the
    first.</p>

   <pre>&lt;p>The &lt;dfn>&lt;abbr title="Garage Door Opener">GDO&lt;/abbr>&lt;/dfn>
is a device that allows off-world teams to open the iris.&lt;/p>
&lt;!-- ... later in the document: -->
&lt;p>Teal'c activated his &lt;abbr title="Garage Door Opener">GDO&lt;/abbr>
and so Hammond ordered the iris to be opened.&lt;/p></pre>
   <!-- XXX need some examples of nesting where the top element makes
   a crossref but the inner ones don't despite also matching the
   algorithm above -->
   <!-- XXX need some examples of duplicates being bad, of title
   attributes being bad, etc -->
   </div>

  <h4 id=the-abbr><span class=secno>3.12.9. </span>The <dfn
   id=abbr><code>abbr</code></dfn> element</h4>

  <p><a href="#strictly">Strictly inline-level content</a>.

  <dl class=element>
   <dt>Contexts in which this element may be used:

   <dd>Where <a href="#strictly">strictly inline-level content</a> is
    allowed.

   <dt>Content model:

   <dd><a href="#strictly">Strictly inline-level content</a>.

   <dt>Element-specific attributes:

   <dd>None, but the <code title=attr-abbr-title><a
    href="#title5">title</a></code> attribute has special semantics on this
    element.

   <dt>DOM interface:

   <dd>No difference from <code><a
    href="#htmlelement">HTMLElement</a></code>.
  </dl>

  <p>The <code><a href="#abbr">abbr</a></code> element represents an
   abbreviation or acronym. The <dfn id=title5
   title=attr-abbr-title><code>title</code></dfn> attribute should be used to
   provide an expansion of the abbreviation. If present, the attribute must
   only contain an expansion of the abbreviation.

  <div class=example>
   <p>The paragraph below contains an abbreviation marked up with the
    <code><a href="#abbr">abbr</a></code> element.</p>

   <pre>&lt;p>The &lt;abbr title="Web Hypertext Application Technology
Working Group">WHATWG&lt;/abbr> is a loose unofficial collaboration of
Web browser manufacturers and interested parties who wish to develop
new technologies designed to allow authors to write and deploy
Applications over the World Wide Web.&lt;/p></pre>
  </div>

  <p>The <code title=attr-abbr-title><a href="#title5">title</a></code>
   attribute may be omitted if there is a <code><a href="#dfn">dfn</a></code>
   element in the document whose <a href="#defining">defining term</a> is the
   abbreviation (the <code><a href="#textcontent">textContent</a></code> of
   the <code><a href="#abbr">abbr</a></code> element).

  <div class=example>
   <p>In the example below, the word "Zat" is used as an abbreviation in the
    second paragraph. The abbreviation is defined in the first, so the
    explanatory <code title=attr-abbr-title><a
    href="#title5">title</a></code> attribute has been omitted. Because of
    the way <code><a href="#dfn">dfn</a></code> elements are defined, the
    second <code><a href="#abbr">abbr</a></code> element in this example
    would be connected (in some UA-specific way) to the first.</p>

   <pre>&lt;p>The &lt;dfn>&lt;abbr>Zat&lt;/abbr>&lt;/dfn>, short for Zat'ni'catel, is a weapon.&lt;/p>
&lt;p>Jack used a &lt;abbr>Zat&lt;/abbr> to make the boxes of evidence disappear.&lt;/p></pre>
  </div>

  <h4 id=the-time><span class=secno>3.12.10. </span>The <dfn
   id=time><code>time</code></dfn> element</h4>

  <p><a href="#strictly">Strictly inline-level content</a>.

  <dl class=element>
   <dt>Contexts in which this element may be used:

   <dd>Where <a href="#strictly">strictly inline-level content</a> is
    allowed.

   <dt>Content model:

   <dd><a href="#strictly">Strictly inline-level content</a>.

   <dt>Element-specific attributes:

   <dd><code title=attr-time-datetime><a href="#datetime">datetime</a></code>

   <dt>DOM interface:

   <dd>
    <pre
     class=idl>interface <dfn id=htmltimeelement>HTMLTimeElement</dfn> : <a href="#htmlelement">HTMLElement</a> {
           attribute DOMString <a href="#datetime0" title=dom-time-datetime>dateTime</a>;
  readonly attribute DOMTimeStamp <a href="#date0" title=dom-time-date>date</a>;
  readonly attribute DOMTimeStamp <a href="#time1" title=dom-time-time>time</a>;
  readonly attribute DOMTimeStamp <a href="#timezone0" title=dom-time-timezone>timezone</a>;
};</pre>
  </dl>

  <p>The <code><a href="#time">time</a></code> element represents a date
   and/or a time.

  <p>The <dfn id=datetime
   title=attr-time-datetime><code>datetime</code></dfn> attribute, if
   present, must contain a <a href="#date-or">date or time string</a> that
   identifies the date or time being specified.

  <p>If the <code title=attr-time-datetime><a
   href="#datetime">datetime</a></code> attribute is not present, then the
   date or time must be specified in the content of the element, such that
   parsing the element's <code><a href="#textcontent">textContent</a></code>
   according to the rules for parsing <a href="#date-or0" title="date or time
   string in content">date or time strings in content</a> successfully
   extracts a date or time.

  <p>The <dfn id=datetime0
   title=dom-time-datetime><code>dateTime</code></dfn> DOM attribute must <a
   href="#reflect">reflect</a> the <code title=attr-time-datetime><a
   href="#datetime">datetime</a></code> content attribute.

  <p>User agents, to obtain the <dfn id=date
   title=concept-time-date>date</dfn>, <dfn id=time0
   title=concept-time-time>time</dfn>, and <dfn id=timezone
   title=concept-time-timezone>timezone</dfn> represented by a <code><a
   href="#time">time</a></code> element, must follow the following steps:

  <ol>
   <li>If the <code title=attr-time-datetime><a
    href="#datetime">datetime</a></code> attribute is present, then parse it
    according to the rules for parsing <a href="#date-or1" title="date or
    time string in attributes">date or time strings in content</a>, and let
    the result be <var title="">result</var>.

   <li>Otherwise, parse the element's <code><a
    href="#textcontent">textContent</a></code> according to the rules for
    parsing <a href="#date-or1" title="date or time string in
    attributes">date or time strings in content</a>, and let the result be
    <var title="">result</var>.

   <li>If <var title="">result</var> is empty (because the parsing failed),
    then the <a href="#date" title=concept-time-date>date</a> is unknown, the
    <a href="#time0" title=concept-time-time>time</a> is unknown, and the <a
    href="#timezone" title=concept-time-timezone>timezone</a> is unknown.

   <li>Otherwise: if <var title="">result</var> contains a date, then that is
    the <a href="#date" title=concept-time-date>date</a>; if <var
    title="">result</var> contains a time, then that is the <a href="#time0"
    title=concept-time-time>time</a>; and if <var title="">result</var>
    contains a timezone, then the timezone is the element's <a
    href="#timezone" title=concept-time-timezone>timezone</a>. (A timezone
    can only be present if both a date and a time are also present.)
  </ol>

  <p>The <dfn id=date0 title=dom-time-date><code>date</code></dfn> DOM
   attribute must return null if the <a href="#date"
   title=concept-time-date>date</a> is unknown, and otherwise must return the
   time corresponding to midnight UTC (i.e. the first second) of the given <a
   href="#date" title=concept-time-date>date</a>.

  <p>The <dfn id=time1 title=dom-time-time><code>time</code></dfn> DOM
   attribute must return null if the <a href="#time0"
   title=concept-time-time>time</a> is unknown, and otherwise must return the
   time corresponding to the given <a href="#time0"
   title=concept-time-time>time</a> of 1970-01-01, with the timezone UTC.

  <p>The <dfn id=timezone0
   title=dom-time-timezone><code>timezone</code></dfn> DOM attribute must
   return null if the <a href="#timezone"
   title=concept-time-timezone>timezone</a> is unknown, and otherwise must
   return the time corresponding to 1970-01-01 00:00 UTC in the given <a
   href="#timezone" title=concept-time-timezone>timezone</a>, with the
   timezone set to UTC (i.e. the time corresponding to 1970-01-01 at 00:00
   UTC plus the offset corresponding to the timezone).

  <div class=example>
   <p>In the following snippet:</p>

   <pre>&lt;p>Our first date was &lt;time datetime="2006-09-23">a saturday&lt;/time>.&lt;/p></pre>

   <p>...the <code><a href="#time">time</a></code> element's <code
    title=dom-time-date><a href="#date0">date</a></code> attribute would have
    the value 1,158,969,600,000ms, and the <code title=dom-time-time><a
    href="#time1">time</a></code> and <code title=dom-time-timezone><a
    href="#timezone0">timezone</a></code> attributes would return null.</p>

   <p>In the following snippet:</p>

   <pre>&lt;p>We stopped talking at &lt;time datetime="2006-09-24 05:00 -7">5am the next morning&lt;/time>.&lt;/p></pre>

   <p>...the <code><a href="#time">time</a></code> element's <code
    title=dom-time-date><a href="#date0">date</a></code> attribute would have
    the value 1,159,056,000,000ms, the <code title=dom-time-time><a
    href="#time1">time</a></code> attribute would have the value
    18,000,000ms, and the <code title=dom-time-timezone><a
    href="#timezone0">timezone</a></code> attribute would return
    -25,200,000ms. To obtain the actual time, the three attributes can be
    added together, obtaining 1,159,048,800,000, which is the specified date
    and time in UTC.</p>

   <p>Finally, in the following snippet:</p>

   <pre>&lt;p>Many people get up at &lt;time>08:00&lt;/time>.&lt;/p></pre>

   <p>...the <code><a href="#time">time</a></code> element's <code
    title=dom-time-date><a href="#date0">date</a></code> attribute would have
    the value null, the <code title=dom-time-time><a
    href="#time1">time</a></code> attribute would have the value
    28,800,000ms, and the <code title=dom-time-timezone><a
    href="#timezone0">timezone</a></code> attribute would return null.</p>
  </div>

  <p class=big-issue>These APIs may be suboptimal. Comments on making them
   more useful to JS authors are welcome. The primary use cases for these
   elements are for marking up publication dates e.g. in blog entries, and
   for marking event dates in hCalendar markup. Thus the DOM APIs are likely
   to be used as ways to generate interactive calendar widgets or some such.

  <h4 id=the-meter><span class=secno>3.12.11. </span>The <dfn
   id=meter><code>meter</code></dfn> element</h4>

  <p><a href="#strictly">Strictly inline-level content</a>.

  <dl class=element>
   <dt>Contexts in which this element may be used:

   <dd>Where <a href="#strictly">strictly inline-level content</a> is
    allowed.

   <dt>Content model:

   <dd><a href="#strictly">Strictly inline-level content</a>.

   <dt>Element-specific attributes:

   <dd><code title=attr-meter-value><a href="#value1">value</a></code>

   <dd><code title=attr-meter-min><a href="#min">min</a></code>

   <dd><code title=attr-meter-low><a href="#low">low</a></code>

   <dd><code title=attr-meter-high><a href="#high">high</a></code>

   <dd><code title=attr-meter-max><a href="#max">max</a></code>

   <dd><code title=attr-meter-optimum><a href="#optimum">optimum</a></code>

   <dt>DOM interface:

   <dd>
    <pre
     class=idl>interface <dfn id=htmlmeterelement>HTMLMeterElement</dfn> : <a href="#htmlelement">HTMLElement</a> {
           attribute long <a href="#value2" title=dom-meter-value>value</a>;
           attribute long <a href="#min0" title=dom-meter-min>min</a>;
           attribute long <a href="#max0" title=dom-meter-max>max</a>;
           attribute long <a href="#low0" title=dom-meter-low>low</a>;
           attribute long <a href="#high0" title=dom-meter-high>high</a>;
           attribute long <a href="#optimum0" title=dom-meter-optimum>optimum</a>;
};</pre>
  </dl>

  <p>The <code><a href="#meter">meter</a></code> element represents a scalar
   measurement within a known range, or a fractional value; for example disk
   usage, the relevance of a query result, or the fraction of a voting
   population to have selected a particular candidate.

  <p>This is also known as a gauge.

  <p class=note>The <code><a href="#meter">meter</a></code> element should
   not be used to indicate progress (as in a progress bar). For that role,
   HTML provides a separate <code><a href="#progress">progress</a></code>
   element.

  <p>There are six attributes that determine the semantics of the gauge
   represented by the element.

  <p>The <dfn id=min title=attr-meter-min><code>min</code></dfn> attribute
   specifies the lower bound of the range, and the <dfn id=max
   title=attr-meter-max><code>max</code></dfn> attribute specifies the upper
   bound. The <dfn id=value1 title=attr-meter-value><code>value</code></dfn>
   attribute specifies the value to have the gauge indicate as the "measured"
   value.

  <p>The other three attributes can be used to segment the gauge's range into
   "low", "medium", and "high" parts, and to indicate which part of the gauge
   is the "optimum" part. The <dfn id=low
   title=attr-meter-low><code>low</code></dfn> attribute specifies the range
   that is considered to be the "low" part, and the <dfn id=high
   title=attr-meter-high><code>high</code></dfn> attribute specifies the
   range that is considered to be the "high" part. The <dfn id=optimum
   title=attr-meter-optimum><code>optimum</code></dfn> attribute gives the
   position that is "optimum"; if that is higher than the "high" value then
   this indicates that the higher the value, the better; if it's lower than
   the "low" mark then it indicates that lower values are better, and
   naturally if it is in between then it indicates that neither high nor low
   values are good.

  <p><strong>Authoring requirements</strong>: The recommended way of giving
   the value is to include it as contents of the element, either as two
   numbers (the higher number represents the maximum, the other number the
   current value), or as a percentage or similar (using one of the characters
   such as "%"), or as a fraction.

  <p>The <code title=attr-meter-value><a href="#value1">value</a></code>,
   <code title=attr-meter-min><a href="#min">min</a></code>, <code
   title=attr-meter-low><a href="#low">low</a></code>, <code
   title=attr-meter-high><a href="#high">high</a></code>, <code
   title=attr-meter-max><a href="#max">max</a></code>, and <code
   title=attr-meter-optimum><a href="#optimum">optimum</a></code> attributes
   are all optional. When present, they must have values that are <a
   href="#valid1" title="valid floating point number">valid floating point
   numbers</a>.

  <div class=example>
   <p>The following examples all represent a measurement of three quarters
    (of the maximum of whatever is being measured):</p>

   <pre>&lt;meter>75%&lt;/meter>
&lt;meter>750&#x2030;&lt;/meter>
&lt;meter>3/4&lt;/meter>
&lt;meter>6 blocks used (out of 8 total)&lt;/meter>
&lt;meter>max: 100; current: 75&lt;/meter>
&lt;meter>&lt;object data="graph75.png">0.75&lt;/object>&lt;/meter>
&lt;meter min="0" max="100" value="75">&lt;/meter></pre>
  </div>

  <p><strong>User agent requirements</strong>: User agents must parse the
   <code title=attr-meter-min><a href="#min">min</a></code>, <code
   title=attr-meter-max><a href="#max">max</a></code>, <code
   title=attr-meter-value><a href="#value1">value</a></code>, <code
   title=attr-meter-low><a href="#low">low</a></code>, <code
   title=attr-meter-high><a href="#high">high</a></code>, and <code
   title=attr-meter-optimum><a href="#optimum">optimum</a></code> attributes
   using the <a href="#rules1">rules for parsing floating point number
   values</a>.

  <p>If the <code title=attr-meter-value><a href="#value1">value</a></code>
   attribute has been omitted, the user agent must also process the <code><a
   href="#textcontent">textContent</a></code> of the element according to the
   <a href="#steps">steps for finding one or two numbers of a ratio in a
   string</a>. These steps will return nothing, one number, one number with a
   denominator punctuation character, or two numbers.

  <p>User agents must then use all these numbers to obtain values for six
   points on the gauge, as follows. (The order in which these are evaluated
   is important, as some of the values refer to earlier ones.)

  <dl>
   <dt>The minimum value

   <dd>
    <p>If the <code title=attr-meter-min><a href="#min">min</a></code>
     attribute is specified and a value could be parsed out of it, then the
     minimum value is that value. Otherwise, the minimum value is zero.</p>

   <dt>The maximum value

   <dd>
    <p>If the <code title=attr-meter-max><a href="#max">max</a></code>
     attribute is specified and a value could be parsed out of it, the
     maximum value is that value.</p>

    <p>Otherwise, if the <code title=attr-meter-max><a
     href="#max">max</a></code> attribute is specified but no value could be
     parsed out of it, or if it was not specified, but either or both of the
     <code title=attr-meter-min><a href="#min">min</a></code> or <code
     title=attr-meter-value><a href="#value1">value</a></code> attributes
     <em>were</em> specified, then the maximum value is 1.</p>

    <p>Otherwise, none of the <code title=attr-meter-max><a
     href="#max">max</a></code>, <code title=attr-meter-min><a
     href="#min">min</a></code>, and <code title=attr-meter-value><a
     href="#value1">value</a></code> attributes were specified. If the result
     of processing the <code><a href="#textcontent">textContent</a></code> of
     the element was either nothing or just one number with no denominator
     punctuation character, then the maximum value is 1; if the result was
     one number but it had an associated denominator punctuation character,
     then the maximum value is the <a href="#a-value" title="values
     associated with denominator punctuation characters">value associated
     with that denominator punctuation character</a>; and finally, if there
     were two numbers parsed out of the <code><a
     href="#textcontent">textContent</a></code>, then the maximum is the
     higher of those two numbers.</p>

    <p>If the above machinations result in a maximum value less than the
     minimum value, then the maximum value is actually the same as the
     minimum value.</p>

   <dt>The actual value

   <dd>
    <p>If the <code title=attr-meter-value><a href="#value1">value</a></code>
     attribute is specified and a value could be parsed out of it, then that
     value is the actual value.</p>

    <p>If the <code title=attr-meter-value><a href="#value1">value</a></code>
     attribute is not specified but the <code title=attr-meter-max><a
     href="#max">max</a></code> attribute <em>is</em> specified and the
     result of processing the <code><a
     href="#textcontent">textContent</a></code> of the element was one number
     with no associated denominator punctuation character, then that number
     is the actual value.</p>

    <p>If neither of the <code title=attr-meter-value><a
     href="#value1">value</a></code> and <code title=attr-meter-max><a
     href="#max">max</a></code> attributes are specified, then, if the result
     of processing the <code><a href="#textcontent">textContent</a></code> of
     the element was one number (with or without an associated denominator
     punctuation character), then that is the actual value, and if the result
     of processing the <code><a href="#textcontent">textContent</a></code> of
     the element was two numbers, then the actual value is the lower of the
     two numbers found.</p>

    <p>Otherwise, if none of the above apply, the actual value is zero.</p>

    <p>If the above procedure results in an actual value less than the
     minimum value, then the actual value is actually the same as the minimum
     value.</p>

    <p>If, on the other hand, the result is an actual value greater than the
     maximum value, then the actual value is the maximum value.</p>

   <dt>The low boundary

   <dd>
    <p>If the <code title=attr-meter-low><a href="#low">low</a></code>
     attribute is specified and a value could be parsed out of it, then the
     low boundary is that value. Otherwise, the low boundary is the same as
     the minimum value.</p>

    <p>If the above results in a low boundary that is less than the minimum
     value, the low boundary is the minimum value.</p>

   <dt>The high boundary

   <dd>
    <p>If the <code title=attr-meter-high><a href="#high">high</a></code>
     attribute is specified and a value could be parsed out of it, then the
     high boundary is that value. Otherwise, the high boundary is the same as
     the maximum value.</p>

    <p>If the above results in a high boundary that is higher than the
     maximum value, the high boundary is the maximum value.</p>

   <dt>The optimum point

   <dd>
    <p>If the <code title=attr-meter-optimum><a
     href="#optimum">optimum</a></code> attribute is specified and a value
     could be parsed out of it, then the optimum point is that value.
     Otherwise, the optimum point is the midpoint between the minimum value
     and the maximum value.</p>

    <p>If the optimum point is then less than the minimum value, then the
     optimum point is actually the same as the minimum value. Similarly, if
     the optimum point is greater than the maximum value, then it is actually
     the maximum value instead.</p>
  </dl>

  <p>All of which should result in the following inequalities all being true:

  <ul class=brief>
   <li>minimum value &le; actual value &le; maximum value

   <li>minimum value &le; low boundary &le; high boundary &le; maximum value

   <li>minimum value &le; optimum point &le; maximum value
  </ul>

  <p><strong>UA requirements for regions of the gauge</strong>: If the
   optimum point is equal to the low boundary or the high boundary, or
   anywhere in between them, then the region between the low and high
   boundaries of the gauge must be treated as the optimum region, and the low
   and high parts, if any, must be treated as suboptimal. Otherwise, if the
   optimum point is less than the low boundary, then the region between the
   minimum value and the low boundary must be treated as the optimum region,
   the region between the low boundary and the high boundary must be treated
   as a suboptimal region, and the region between the high boundary and the
   maximum value must be treated as an even less good region. Finally, if the
   optimum point is higher than the high boundary, then the situation is
   reversed; the region between the high boundary and the maximum value must
   be treated as the optimum region, the region between the high boundary and
   the low boundary must be treated as a suboptimal region, and the remaining
   region between the low boundary and the minimum value must be treated as
   an even less good region.

  <p><strong>UA requirements for showing the gauge</strong>: When
   representing a <code><a href="#meter">meter</a></code> element to the
   user, the UA should indicate the relative position of the actual value to
   the minimum and maximum values, and the relationship between the actual
   value and the three regions of the gauge.

  <div class=example>
   <p>The following markup:</p>

   <pre>
&lt;h3>Suggested groups&lt;/h3>
&lt;menu type="toolbar">
 &lt;a href="?cmd=hsg" onclick="hideSuggestedGroups()">Hide suggested groups&lt;/a>
&lt;/menu>
&lt;ul>
 &lt;li>
  &lt;p>&lt;a href="/group/comp.infosystems.www.authoring.stylesheets/view">comp.infosystems.www.authoring.stylesheets&lt;/a> -
     &lt;a href="/group/comp.infosystems.www.authoring.stylesheets/subscribe">join&lt;/a>&lt;/p>
  &lt;p>Group description: &lt;strong>Layout/presentation on the WWW.&lt;/strong>&lt;/p>
  &lt;p><strong>&lt;meter value="0.5">Moderate activity,&lt;/meter></strong> Usenet, 618 subscribers&lt;/p>
 &lt;/li>
 &lt;li>
  &lt;p>&lt;a href="/group/netscape.public.mozilla.xpinstall/view">netscape.public.mozilla.xpinstall&lt;/a> -
     &lt;a href="/group/netscape.public.mozilla.xpinstall/subscribe">join&lt;/a>&lt;/p>
  &lt;p>Group description: &lt;strong>Mozilla XPInstall discussion.&lt;/strong>&lt;/p>
  &lt;p><strong>&lt;meter value="0.25">Low activity,&lt;/meter></strong> Usenet, 22 subscribers&lt;/p>
 &lt;/li>
 &lt;li>
  &lt;p>&lt;a href="/group/mozilla.dev.general/view">mozilla.dev.general&lt;/a> -
     &lt;a href="/group/mozilla.dev.general/subscribe">join&lt;/a>&lt;/p>
  &lt;p><strong>&lt;meter value="0.25">Low activity,&lt;/meter></strong> Usenet, 66 subscribers&lt;/p>
 &lt;/li>
&lt;/ul>
</pre>

   <p>Might be rendered as follows:</p>

   <p><img alt="With the &lt;meter> elements rendered as inline green bars of
    varying lengths." src="images/sample-meter.png"></p>
  </div>

  <p>The <dfn id=min0 title=dom-meter-min><code>min</code></dfn>, <dfn
   id=max0 title=dom-meter-max><code>max</code></dfn>, <dfn id=value2
   title=dom-meter-value><code>value</code></dfn>, <dfn id=low0
   title=dom-meter-low><code>low</code></dfn>, <dfn id=high0
   title=dom-meter-high><code>high</code></dfn>, and <dfn id=optimum0
   title=dom-meter-optimum><code>optimum</code></dfn> DOM attributes must
   reflect the elements' content attributes of the same name. When the
   relevant content attributes are absent, the DOM attributes must return
   zero. The value parsed from the <code><a
   href="#textcontent">textContent</a></code> never affects the DOM values.

  <p class=big-issue>Would be cool to have the <code title=dom-meter-value><a
   href="#value2">value</a></code> DOM attribute update the <code><a
   href="#textcontent">textContent</a></code> in-line...</p>
  <!-- XXX
should we also look inside the title="" attribute?
   Disk usage: <meter title="985MB of 986MB total" high="980">Full!</meter>
should we make the contents accessible in some way, e.g. as a tooltip?
-->

  <h4 id=the-progress><span class=secno>3.12.12. </span>The <dfn
   id=progress><code>progress</code></dfn> element</h4>

  <p><a href="#strictly">Strictly inline-level content</a>.

  <dl class=element>
   <dt>Contexts in which this element may be used:

   <dd>Where <a href="#strictly">strictly inline-level content</a> is
    allowed.

   <dt>Content model:

   <dd><a href="#strictly">Strictly inline-level content</a>.

   <dt>Element-specific attributes:

   <dd><code title=attr-progress-value><a href="#value3">value</a></code>

   <dd><code title=attr-progress-max><a href="#max1">max</a></code>

   <dt>DOM interface:

   <dd>
    <pre
     class=idl>interface <dfn id=htmlprogresselement>HTMLProgressElement</dfn> : <a href="#htmlelement">HTMLElement</a> {
           attribute float <a href="#value4" title=dom-progress-value>value</a>;
           attribute float <a href="#max2" title=dom-progress-max>max</a>;
  readonly attribute float <a href="#position" title=dom-progress-position>position</a>;
};</pre>
  </dl>

  <p>The <code><a href="#progress">progress</a></code> element represents the
   completion progress of a task. The progress is either indeterminate,
   indicating that progress is being made but that it is not clear how much
   more work remains to be done before the task is complete (e.g. because the
   task is waiting for a remote host to respond), or the progress is a number
   in the range zero to a maximum, giving the fraction of work that has so
   far been completed.

  <p>There are two attributes that determine the current task completion
   represented by the element.

  <p>The <dfn id=value3 title=attr-progress-value><code>value</code></dfn>
   attribute specifies how much of the task has been completed, and the <dfn
   id=max1 title=attr-progress-max><code>max</code></dfn> attribute specifies
   how much work the task requires in total. The units are arbitrary and not
   specified.

  <p>Instead of using the attributes, authors are recommended to simply
   include the current value and the maximum value inline as text inside the
   element.

  <div class=example>
   <p>Here is a snippet of a Web application that shows the progress of some
    automated task:</p>

   <pre>&lt;section>
 &lt;h2>Task Progress&lt;/h2>
 &lt;p>&lt;label>Progress: &lt;progress>&lt;span id="p">0&lt;/span>%&lt;/progress>&lt;/p>
 &lt;script>
  var progressBar = document.getElementById('p');
  function updateProgress(newValue) {
    progressBar.textContent = newValue;
  }
 &lt;/script>
&lt;/section></pre>

   <p>(The <code>updateProgress()</code> method in this example would be
    called by some other code on the page to update the actual progress bar
    as the task progressed.)</p>
  </div>

  <p><strong>Author requirements</strong>: The <code
   title=attr-progress-max><a href="#max1">max</a></code> and <code
   title=attr-progress-value><a href="#value3">value</a></code> attributes,
   when present, must have values that are <a href="#valid1" title="valid
   floating point number">valid floating point numbers</a>. The <code
   title=attr-progress-max><a href="#max1">max</a></code> attribute, if
   present, must have a value greater than zero. The <code
   title=attr-progress-value><a href="#value3">value</a></code> attribute, if
   present, must have a value equal to or greater than zero, and less than or
   equal to the value of the <code title=attr-progress-max><a
   href="#max1">max</a></code> attribute, if present.

  <p><strong>User agent requirements</strong>: User agents must parse the
   <code title=attr-progress-max><a href="#max1">max</a></code> and <code
   title=attr-progress-value><a href="#value3">value</a></code> attributes'
   values according to the <a href="#rules1">rules for parsing floating point
   number values</a>.

  <p>If the <code title=attr-progress-value><a
   href="#value3">value</a></code> attribute is omitted, then user agents
   must also parse the <code><a href="#textcontent">textContent</a></code> of
   the <code><a href="#progress">progress</a></code> element in question
   using the <a href="#steps">steps for finding one or two numbers of a ratio
   in a string</a>. These steps will return nothing, one number, one number
   with a denominator punctuation character, or two numbers.

  <p>Using the results of this processing, user agents must determine whether
   the progress bar is an indeterminate progress bar, or whether it is a
   determinate progress bar, and in the latter case, what its current and
   maximum values are, all as follows:

  <ol>
   <li>If the <code title=attr-progress-max><a href="#max1">max</a></code>
    attribute is omitted, and the <code title=attr-progress-value><a
    href="#value3">value</a></code> is omitted, and the results of parsing
    the <code><a href="#textcontent">textContent</a></code> was nothing, then
    the progress bar is an indeterminate progress bar. Abort these steps.

   <li>Otherwise, it is a determinate progress bar.

   <li>If the <code title=attr-progress-max><a href="#max1">max</a></code>
    attribute is included, then, if a value could be parsed out of it, then
    the maximum value is that value.

   <li>Otherwise, if the <code title=attr-progress-max><a
    href="#max1">max</a></code> attribute is absent but the <code
    title=attr-progress-value><a href="#value3">value</a></code> attribute is
    present, or, if the <code title=attr-progress-max><a
    href="#max1">max</a></code> attribute is present but no value could be
    parsed from it, then the maximum is 1.

   <li>Otherwise, if neither attribute is included, then, if the <code><a
    href="#textcontent">textContent</a></code> contained one number with an
    associated denominator punctuation character, then the maximum value is
    the <span>value associated with that denominator punctuation
    character</span>; otherwise, if the <code><a
    href="#textcontent">textContent</a></code> contained two numbers, the
    maximum value is the higher of the two values; otherwise, the maximum
    value is 1.

   <li>If the <code title=attr-progress-value><a
    href="#value3">value</a></code> attribute is present on the element and a
    value could be parsed out of it, that value is the current value of the
    progress bar. Otherwise, if the attribute is present but no value could
    be parsed from it, the current value is zero.

   <li>Otherwise if the <code title=attr-progress-value><a
    href="#value3">value</a></code> attribute is absent and the <code
    title=attr-progress-max><a href="#max1">max</a></code> attribute is
    present, then, if the <code><a href="#textcontent">textContent</a></code>
    was parsed and found to contain just one number, with no associated
    denominator punctuation character, then the current value is that number.
    Otherwise, if the <code title=attr-progress-value><a
    href="#value3">value</a></code> attribute is absent and the <code
    title=attr-progress-max><a href="#max1">max</a></code> attribute is
    present then the current value is zero.

   <li>Otherwise, if neither attribute is present, then the current value is
    the lower of the one or two numbers that were found in the <code><a
    href="#textcontent">textContent</a></code> of the element.

   <li>If the maximum value is less than or equal to zero, then it is reset
    to 1.

   <li>If the current value is less than zero, then it is reset to zero.

   <li>Finally, if the current value is greater than the maximum value, then
    the current value is reset to the maximum value.
  </ol>

  <p><strong>UA requirements for showing the progress bar</strong>: When
   representing a <code><a href="#progress">progress</a></code> element to
   the user, the UA should indicate whether it is a determinate or
   indeterminate progress bar, and in the former case, should indicate the
   relative position of the current value relative to the maximum value.

  <p>The <dfn id=max2 title=dom-progress-max><code>max</code></dfn> and <dfn
   id=value4 title=dom-progress-value><code>value</code></dfn> DOM attributes
   must reflect the elements' content attributes of the same name. When the
   relevant content attributes are absent, the DOM attributes must return
   zero. The value parsed from the <code><a
   href="#textcontent">textContent</a></code> never affects the DOM values.

  <p class=big-issue>Would be cool to have the <code
   title=dom-progress-value><a href="#value4">value</a></code> DOM attribute
   update the <code><a href="#textcontent">textContent</a></code> in-line...

  <p>If the progress bar is an indeterminate progress bar, then the <dfn
   id=position title=dom-progress-position><code>position</code></dfn> DOM
   attribute must return -1. Otherwise, it must return the result of dividing
   the current value by the maximum value.

  <h4 id=the-code><span class=secno>3.12.13. </span>The <dfn
   id=code><code>code</code></dfn> element</h4>

  <p><a href="#strictly">Strictly inline-level content</a>.

  <dl class=element>
   <dt>Contexts in which this element may be used:

   <dd>Where <a href="#strictly">strictly inline-level content</a> is
    allowed.

   <dt>Content model:

   <dd>When used in an element whose content model is only <a
    href="#strictly">strictly inline-level content</a>: only <a
    href="#strictly">strictly inline-level content</a>.

   <dd>Otherwise: any <a href="#inline-level0">inline-level content</a>.

   <dt>Element-specific attributes:

   <dd>None, but the <code title=attr-title><a href="#title">title</a></code>
    attribute has special semantics on this element when used with the
    <code><a href="#dfn">dfn</a></code> element.

   <dt>DOM interface:

   <dd>No difference from <code><a
    href="#htmlelement">HTMLElement</a></code>.
  </dl>

  <p>The <code><a href="#code">code</a></code> element represents a fragment
   of computer code. This could be an XML element name, a filename, a
   computer program, or any other string that a computer would recognise.

  <p class=note>See the <code><a href="#pre">pre</a></code> element for more
   detais.

  <div class=example>
   <p>The following example shows how a block of code could be marked up
    using the <code><a href="#pre">pre</a></code> and <code><a
    href="#code">code</a></code> elements.</p>

   <pre>&lt;pre>&lt;code>var i: Integer;
begin
   i := 1;
end.&lt;/code>&lt;/pre></pre>
  </div>

  <h4 id=the-var><span class=secno>3.12.14. </span>The <dfn
   id=var><code>var</code></dfn> element</h4>

  <p><a href="#strictly">Strictly inline-level content</a>.

  <dl class=element>
   <dt>Contexts in which this element may be used:

   <dd>Where <a href="#strictly">strictly inline-level content</a> is
    allowed.

   <dt>Content model:

   <dd><a href="#strictly">Strictly inline-level content</a>.

   <dt>Element-specific attributes:

   <dd>None, but the <code title=attr-title><a href="#title">title</a></code>
    attribute has special semantics on this element when used with the
    <code><a href="#dfn">dfn</a></code> element.

   <dt>DOM interface:

   <dd>No difference from <code><a
    href="#htmlelement">HTMLElement</a></code>.
  </dl>

  <p>The <code><a href="#var">var</a></code> element represents a variable.
   This could be an actual variable in a mathematical expression or
   programming context, or it could just be a term used as a placeholder in
   prose.

  <div class=example>
   <p>In the paragraph below, the letter "n" is being used as a variable in
    prose:</p>

   <pre>&lt;p>If there are &lt;var>n&lt;/var> pipes leading to the ice
cream factory then I expect at &lt;em>least&lt;/em> &lt;var>n&lt;/var>
flavours of ice cream to be available for purchase!&lt;/p></pre>
  </div>

  <h4 id=the-samp><span class=secno>3.12.15. </span>The <dfn
   id=samp><code>samp</code></dfn> element</h4>

  <p><a href="#strictly">Strictly inline-level content</a>.

  <dl class=element>
   <dt>Contexts in which this element may be used:

   <dd>Where <a href="#strictly">strictly inline-level content</a> is
    allowed.

   <dt>Content model:

   <dd>When used in an element whose content model is only <a
    href="#strictly">strictly inline-level content</a>: only <a
    href="#strictly">strictly inline-level content</a>.

   <dd>Otherwise: any <a href="#inline-level0">inline-level content</a>.

   <dt>Element-specific attributes:

   <dd>None, but the <code title=attr-title><a href="#title">title</a></code>
    attribute has special semantics on this element when used with the
    <code><a href="#dfn">dfn</a></code> element.

   <dt>DOM interface:

   <dd>No difference from <code><a
    href="#htmlelement">HTMLElement</a></code>.
  </dl>

  <p>The <code><a href="#samp">samp</a></code> element represents (sample)
   output from a program or computing system.

  <p class=note>See the <code><a href="#pre">pre</a></code> and <code><a
   href="#kbd">kbd</a></code> elements for more detais.

  <div class=example>
   <p>This example shows the <code><a href="#samp">samp</a></code> element
    being used inline:</p>

   <pre>&lt;p>The computer said &lt;samp>Too much cheese in tray
two&lt;/samp> but I didn't know what that meant.&lt;/p></pre>

   <p>This second example shows a block of sample output. Nested <code><a
    href="#samp">samp</a></code> and <code><a href="#kbd">kbd</a></code>
    elements allow for the styling of specific elements of the sample output
    using a style sheet.</p>
   <!-- XXX should those nested SAMPs be SPANs? -->
   <pre>&lt;pre>&lt;samp>&lt;samp class="prompt">jdoe@mowmow:~$&lt;/samp> &lt;kbd>ssh demo.example.com&lt;/kbd>
Last login: Tue Apr 12 09:10:17 2005 from mowmow.example.com on pts/1
Linux demo 2.6.10-grsec+gg3+e+fhs6b+nfs+gr0501+++p3+c4a+gr2b-reslog-v6.189 #1 SMP Tue Feb 1 11:22:36 PST 2005 i686 unknown

&lt;samp class="prompt">jdoe@demo:~$&lt;/samp> &lt;samp class="cursor">_&lt;/samp>&lt;/samp>&lt;/pre></pre>
  </div>

  <h4 id=the-kbd><span class=secno>3.12.16. </span>The <dfn
   id=kbd><code>kbd</code></dfn> element</h4>

  <p><a href="#strictly">Strictly inline-level content</a>.

  <dl class=element>
   <dt>Contexts in which this element may be used:

   <dd>Where <a href="#strictly">strictly inline-level content</a> is
    allowed.

   <dt>Content model:

   <dd><a href="#strictly">Strictly inline-level content</a>.

   <dt>Element-specific attributes:

   <dd>None.

   <dt>DOM interface:

   <dd>No difference from <code><a
    href="#htmlelement">HTMLElement</a></code>.
  </dl>

  <p>The <code><a href="#kbd">kbd</a></code> element represents user input
   (typically keyboard input, although it may also be used to represent other
   input, such as voice commands).

  <p>When the <code><a href="#kbd">kbd</a></code> element is nested inside a
   <code><a href="#samp">samp</a></code> element, it represents the input as
   it was echoed by the system.

  <p>When the <code><a href="#kbd">kbd</a></code> element <em>contains</em> a
   <code><a href="#samp">samp</a></code> element, it represents input based
   on system output, for example invoking a menu item.

  <p>When the <code><a href="#kbd">kbd</a></code> element is nested inside
   another <code><a href="#kbd">kbd</a></code> element, it represents an
   actual key or other single unit of input as appropriate for the input
   mechanism.

  <div class=example>
   <p>Here the <code><a href="#kbd">kbd</a></code> element is used to
    indicate keys to press:</p>

   <pre>&lt;p>To make George eat an apple, press &lt;kbd>&lt;kbd>Shift&lt;/kbd>+&lt;kbd>F3&lt;/kbd>&lt;/kbd>&lt;/p></pre>

   <p>In this second example, the user is told to pick a particular menu
    item. The outer <code><a href="#kbd">kbd</a></code> element marks up a
    block of input, with the inner <code><a href="#kbd">kbd</a></code>
    elements representing each individual step of the input, and the <code><a
    href="#samp">samp</a></code> elements inside them indicating that the
    steps are input based on something being displayed by the system, in this
    case menu labels:</p>

   <pre>&lt;p>To make George eat an apple, select
    &lt;kbd>&lt;kbd>&lt;samp>File&lt;/samp>&lt;/kbd>|&lt;kbd>&lt;samp>Eat Apple...&lt;/samp>&lt;/kbd>&lt;/kbd>
&lt;/p></pre>
  </div>

  <h4 id=the-sup><span class=secno>3.12.17. </span>The <dfn
   id=sup><code>sup</code></dfn> and <dfn id=sub><code>sub</code></dfn>
   elements</h4>

  <p><a href="#strictly">Strictly inline-level content</a>.

  <dl class=element>
   <dt>Contexts in which these elements may be used:

   <dd>Where <a href="#strictly">strictly inline-level content</a> is
    allowed.

   <dt>Content model:

   <dd><a href="#strictly">Strictly inline-level content</a>.

   <dt>Element-specific attributes:

   <dd>None.

   <dt>DOM interface:

   <dd>No difference from <code><a
    href="#htmlelement">HTMLElement</a></code>.
  </dl>

  <p>The <code><a href="#sup">sup</a></code> element represents a superscript
   and the <code><a href="#sub">sub</a></code> element represents a
   subscript.

  <p>These elements must only be used to mark up typographical conventions
   with specific meanings, not for typographical presentation for
   presentation's sake. For example, it would be inappropriate for the
   <code><a href="#sup">sup</a></code> and <code><a
   href="#sub">sub</a></code> elements to be used in the name of the LaTeX
   document preparation system. In general, authors should not use these
   elements if the <em>absence</em> of those elements would not change the
   meaning of the content.

  <p>When the <code><a href="#sub">sub</a></code> element is used inside a
   <code><a href="#var">var</a></code> element, it represents the subscript
   that identifies the variable in a family of variables.

  <div class=example>
   <pre>&lt;p>The coordinate of the &lt;var>i&lt;/var>th point is
(&lt;var>x&lt;sub>&lt;var>i&lt;/var>&lt;/sub>&lt;/var>, &lt;var>y&lt;sub>&lt;var>i&lt;/var>&lt;/sub>&lt;/var>).
For example, the 10th point has coordinate
(&lt;var>x&lt;sub>10&lt;/sub>&lt;/var>, &lt;var>y&lt;sub>10&lt;/sub>&lt;/var>).&lt;/p></pre>
  </div>

  <p>In certain languages, superscripts are part of the typographical
   conventions for some abbreviations.

  <div class=example>
   <pre>&lt;p>The most beautiful women are
&lt;span lang="fr">&lt;abbr>M&lt;sup>lle&lt;/sup>&lt;/abbr> Gwendoline&lt;/span> and 
&lt;span lang="fr">&lt;abbr>M&lt;sup>me&lt;/sup>&lt;/abbr> Denise&lt;/span>.&lt;/p></pre>
  </div>

  <p>Mathematical expressions often use subscripts and superscripts.
   <!--Authors are encouraged to use MathML for marking up mathematics,
  but authors may opt to use <code>sub</code> and <code>sup</code> if
  detailed mathematical markup is not desired. <a
  href="#refsMathML">[MathML]</a>--></p>
  <!-- XXX -->

  <div class=example>
   <pre>&lt;var>E&lt;/var>=&lt;var>m&lt;/var>&lt;var>c&lt;/var>&lt;sup>2&lt;/sup></pre>

   <pre>f(&lt;var>x&lt;/var>, &lt;var>n&lt;/var>) = log&lt;sub>4&lt;/sub>&lt;var>x&lt;/var>&lt;sup>&lt;var>n&lt;/var>&lt;/sup></pre>
  </div>

  <h4 id=the-span><span class=secno>3.12.18. </span>The <dfn
   id=span><code>span</code></dfn> element</h4>

  <p><a href="#strictly">Strictly inline-level content</a>.

  <dl class=element>
   <dt>Contexts in which this element may be used:

   <dd>Where <a href="#strictly">strictly inline-level content</a> is
    allowed.

   <dt>Content model:

   <dd>When used in an element whose content model is only <a
    href="#strictly">strictly inline-level content</a>: only <a
    href="#strictly">strictly inline-level content</a>.

   <dd>Otherwise: any <a href="#inline-level0">inline-level content</a>.

   <dt>Element-specific attributes:

   <dd>None, but the <code title=attr-title><a href="#title">title</a></code>
    attribute has special semantics on this element when used with the
    <code><a href="#dfn">dfn</a></code> element.

   <dt>DOM interface:

   <dd>No difference from <code><a
    href="#htmlelement">HTMLElement</a></code>.
  </dl>

  <p>The <code><a href="#span">span</a></code> element doesn't mean anything
   on its own, but can be useful when used together with other attributes,
   e.g. <code title=attr-class><a href="#class">class</a></code>, <code
   title=attr-lang><a href="#lang">lang</a></code>, or <code
   title=attr-dir><a href="#dir">dir</a></code>, or when used in conjunction
   with the <code><a href="#dfn">dfn</a></code> element.</p>
  <!-- XXX need examples -->

  <h4 id=the-i><span class=secno>3.12.19. </span>The <dfn
   id=i><code>i</code></dfn> element</h4>

  <p><a href="#strictly">Strictly inline-level content</a>.

  <dl class=element>
   <dt>Contexts in which this element may be used:

   <dd>Where <a href="#strictly">strictly inline-level content</a> is
    allowed.

   <dt>Content model:

   <dd><a href="#strictly">Strictly inline-level content</a>.

   <dt>Element-specific attributes:

   <dd>None, but the <code title=attr-title><a href="#title">title</a></code>
    attribute has special semantics on this element when used with the
    <code><a href="#dfn">dfn</a></code> element.

   <dt>DOM interface:

   <dd>No difference from <code><a
    href="#htmlelement">HTMLElement</a></code>.
  </dl>

  <p>The <code><a href="#i">i</a></code> element represents a span of text in
   an alternate voice or mood, or otherwise offset from the normal prose,
   such as a taxonomic designation, a technical term, an idiomatic phrase
   from another language, a thought, a ship name, or some other prose whose
   typical typographic presentation is italicized.

  <p>Terms in languages different from the main text should be annotated with
   <code title=attr-lang><a href="#lang">lang</a></code> attributes (<code
   title=attr-xml-lang><a href="#xmllang">xml:lang</a></code> in XML).

  <div class=example>
   <p>The examples below show uses of the <code><a href="#i">i</a></code>
    element:</p>

   <pre>&lt;p>The &lt;i>felis silvestris catus&lt;/i> is cute.&lt;/p>
&lt;p>The &lt;i>block-level elements&lt;/i> are defined above.&lt;/p>
&lt;p>There is a certain &lt;i lang="fr">je ne sais quoi&lt;/i> in the air.&lt;/p></pre>

   <p>In the following example, a dream sequence is marked up using <code><a
    href="#i">i</a></code> elements.</p>

   <pre>&lt;p>Raymond tried to sleep.&lt;/p>
&lt;p>&lt;i>The ship sailed away on Thursday&lt;/i>, he
dreamt. &lt;i>The ship had many people aboard, including a beautiful
princess called Carey. He watched her, day-in, day-out, hoping she
would notice him, but she never did.&lt;/i>&lt;/p>
&lt;p>&lt;i>Finally one night he picked up the courage to speak with
her&mdash;&lt;/i>&lt;/p>
&lt;p>Raymond woke with a start as the fire alarm rang out.&lt;/p></pre>
  </div>

  <p>The <code><a href="#i">i</a></code> element should be used as a last
   resort when no other element is more appropriate. In particular, citations
   should use the <code><a href="#cite2">cite</a></code> element, defining
   instances of terms should use the <code><a href="#dfn">dfn</a></code>
   element, stress emphasis should use the <code><a href="#em">em</a></code>
   element, importance should be denoted with the <code><a
   href="#strong">strong</a></code> element, quotes should be marked up with
   the <code><a href="#q">q</a></code> element, and small print should use
   the <code><a href="#small">small</a></code> element.

  <p class=note>Style sheets can be used to format <code><a
   href="#i">i</a></code> elements, just like any other element can be
   restyled. Thus, it is not the case that content in <code><a
   href="#i">i</a></code> elements will necessarily be italicised.

  <h4 id=the-b><span class=secno>3.12.20. </span>The <dfn
   id=b><code>b</code></dfn> element</h4>

  <p><a href="#strictly">Strictly inline-level content</a>.

  <dl class=element>
   <dt>Contexts in which this element may be used:

   <dd>Where <a href="#strictly">strictly inline-level content</a> is
    allowed.

   <dt>Content model:

   <dd><a href="#strictly">Strictly inline-level content</a>.

   <dt>Element-specific attributes:

   <dd>None.

   <dt>DOM interface:

   <dd>No difference from <code><a
    href="#htmlelement">HTMLElement</a></code>.
  </dl>

  <p>The <code><a href="#b">b</a></code> element represents a span of text to
   be stylistically offset from the normal prose without conveying any extra
   importance, such as key words in a document abstract, product names in a
   review, or other spans of text whose typical typographic presentation is
   boldened.

  <div class=example>
   <p>The following example shows a use of the <code><a
    href="#b">b</a></code> element to highlight key words without marking
    them up as important:</p>

   <pre>&lt;p>The &lt;b>frobonitor&lt;/b> and &lt;b>barbinator&lt;/b> components are fried.&lt;/p></pre>

   <p>The following would be <em>incorrect</em> usage:</p>

   <pre>&lt;p>&lt;b>WARNING!&lt;/b> Do not frob the barbinator!&lt;/p></pre>

   <p>In the previous example, the correct element to use would have been
    <code><a href="#strong">strong</a></code>, not <code><a
    href="#b">b</a></code>.</p>

   <p>In the following example, objects in a text adventure are highlighted
    as being special by use of the <code><a href="#b">b</a></code> element.</p>

   <pre>&lt;p>You enter a small room. Your &lt;b>sword&lt;/b> glows
brighter. A &lt;b>rat&lt;/b> scurries past the corner wall.&lt;/p></pre>
  </div>

  <p>The <code><a href="#b">b</a></code> element should be used as a last
   resort when no other element is more appropriate. In particular, headers
   should use the <code><a href="#h1">h1</a></code> to <code><a
   href="#h6">h6</a></code> elements, stress emphasis should use the <code><a
   href="#em">em</a></code> element, importance should be denoted with the
   <code><a href="#strong">strong</a></code> element, and text marked or
   highlighted should use the <code><a href="#m">m</a></code> element.

  <p class=note>Style sheets can be used to format <code><a
   href="#b">b</a></code> elements, just like any other element can be
   restyled. Thus, it is not the case that content in <code><a
   href="#b">b</a></code> elements will necessarily be boldened.

  <h4 id=the-bdo><span class=secno>3.12.21. </span>The <dfn
   id=bdo><code>bdo</code></dfn> element</h4>

  <p><a href="#strictly">Strictly inline-level content</a>.

  <dl class=element>
   <dt>Contexts in which this element may be used:

   <dd>Where <a href="#strictly">strictly inline-level content</a> is
    allowed.

   <dt>Content model:

   <dd><a href="#strictly">Strictly inline-level content</a>.

   <dt>Element-specific attributes:

   <dd>None, but the <code title=attr-dir><a href="#dir">dir</a></code>
    global attribute is required on this element.

   <dt>DOM interface:

   <dd>No difference from <code><a
    href="#htmlelement">HTMLElement</a></code>.
  </dl>

  <p>The <code><a href="#bdo">bdo</a></code> element allows authors to
   override the Unicode bidi algorithm by explicitly specifying a direction
   override. <a href="#refsBIDI">[BIDI]</a>

  <p>Authors must specify the <code title=attr-dir><a
   href="#dir">dir</a></code> attribute on this element, with the value
   <code>ltr</code> to specify a left-to-right override and with the value
   <code>rtl</code> to specify a right-to-left override.

  <p>If the element has the <code title=attr-dir><a
   href="#dir">dir</a></code> attribute set to the exact value
   <code>ltr</code>, then for the purposes of the bidi algorithm, the user
   agent must act as if there was a U+202D LEFT-TO-RIGHT OVERRIDE character
   at the start of the element, and a U+202C POP DIRECTIONAL FORMATTING at
   the end of the element.

  <p>If the element has the <code title=attr-dir><a
   href="#dir">dir</a></code> attribute set to the exact value
   <code>rtl</code>, then for the purposes of the bidi algorithm, the user
   agent must act as if there was a U+202E RIGHT-TO-LEFT OVERRIDE character
   at the start of the element, and a U+202C POP DIRECTIONAL FORMATTING at
   the end of the element.

  <p>The requirements on handling the <code><a href="#bdo">bdo</a></code>
   element for the bidi algorithm may be implemented indirectly through the
   style layer. For example, an HTML+CSS user agent should implement these
   requirements by implementing the CSS <code>unicode-bidi</code> property.
   <a href="#refsCSS21">[CSS21]</a></p>
  <!-- XXX need examples -->

  <h3 id=edits><span class=secno>3.13. </span>Edits</h3>

  <p>The <code><a href="#ins">ins</a></code> and <code><a
   href="#del">del</a></code> elements represent edits to the document.

  <h4 id=the-ins><span class=secno>3.13.1. </span>The <dfn
   id=ins><code>ins</code></dfn> element</h4>

  <p><a href="#transparent0">Transparent</a> <a href="#block-level0"
   title="block-level elements">block-level element</a>, and <a
   href="#transparent0">transparent</a> <a href="#strictly">strictly
   inline-level content</a>.

  <dl class=element>
   <dt>Contexts in which this element may be used:

   <dd>Where <a href="#block-level0">block-level elements</a> is expected.

   <dd>Where <a href="#strictly">strictly inline-level content</a> is
    allowed.

   <dt>Content model:

   <dd><a href="#transparent0">Transparent</a>.

   <dt>Element-specific attributes:

   <dd><code title=attr-mod-cite><a href="#cite3">cite</a></code>

   <dd><code title=attr-mod-datetime><a href="#datetime1">datetime</a></code>

   <dt>DOM interface:

   <dd>Uses the <code><a href="#htmlmodelement">HTMLModElement</a></code>
    interface.
  </dl>

  <p>The <code><a href="#ins">ins</a></code> element represents an addition
   to the document.

  <p>The <code><a href="#ins">ins</a></code> element must be used only where
   <a href="#block-level0">block-level elements</a> or <a
   href="#strictly">strictly inline-level content</a> can be used.

  <p>An <code><a href="#ins">ins</a></code> element can only contain content
   that would still be conformant if all elements with <a
   href="#transparent0">transparent</a> content models were replaced by their
   contents.

  <div class=example>
   <p>The following would be syntactically legal:</p>

   <pre>&lt;aside>
 &lt;ins>
  &lt;p>...&lt;/p>
 &lt;/ins>
&lt;/aside></pre>

   <p>As would this:</p>

   <pre>&lt;aside>
 &lt;ins>
  &lt;em>...&lt;/em>
 &lt;/ins>
&lt;/aside></pre>

   <p>However, this last example would be illegal, as <code><a
    href="#em">em</a></code> and <code><a href="#p">p</a></code> cannot both
    be used inside an <code><a href="#aside">aside</a></code> element at the
    same time:</p>

   <pre>&lt;aside>
 &lt;ins>
  &lt;p>...&lt;/p>
 &lt;/ins>
 &lt;ins>
  &lt;em>...&lt;/em>
 &lt;/ins>
&lt;/aside></pre>
  </div>

  <h4 id=the-del><span class=secno>3.13.2. </span>The <dfn
   id=del><code>del</code></dfn> element</h4>

  <p><a href="#block-level0" title="block-level elements">Block-level
   element</a>, and <a href="#strictly">strictly inline-level content</a>.

  <dl class=element>
   <dt>Contexts in which this element may be used:

   <dd>Where <a href="#block-level0">block-level elements</a> is expected.

   <dd>Where <a href="#strictly">strictly inline-level content</a> is
    allowed.

   <dt>Content model:

   <dd>When the element has a parent: same content model as the parent
    element (without taking into account the other children of the parent
    element).

   <dd>Otherwise: zero or more <a href="#block-level0">block-level
    elements</a>, or <a href="#inline-level0">inline-level content</a> (but
    not both).

   <dt>Element-specific attributes:

   <dd><code title=attr-mod-cite><a href="#cite3">cite</a></code>

   <dd><code title=attr-mod-datetime><a href="#datetime1">datetime</a></code>

   <dt>DOM interface:

   <dd>Uses the <code><a href="#htmlmodelement">HTMLModElement</a></code>
    interface.
  </dl>

  <p>The <code><a href="#del">del</a></code> element represents a removal
   from the document.

  <p>The <code><a href="#del">del</a></code> element must only contain
   content that would be allowed inside the parent element (regardless of
   what the parent element actually contains).

  <div class=example>
   <p>The following would be syntactically legal:</p>

   <pre>&lt;aside>
 &lt;del>
  &lt;p>...&lt;/p>
 &lt;/del>
 &lt;ins>
  &lt;em>...&lt;/em>
 &lt;/ins>
&lt;/aside></pre>

   <p>...even though the <code><a href="#p">p</a></code> and <code><a
    href="#em">em</a></code> elements would never be allowed side by side in
    the <code><a href="#aside">aside</a></code> element. This is allowed
    because the <code><a href="#del">del</a></code> element represents
    content that was removed, and it is quite possible that an edit could
    cause an element to go from being an inline-level container to a
    block-level container, or vice-versa.</p>
  </div>

  <h4 id=attributes><span class=secno>3.13.3. </span>Attributes common to
   <code><a href="#ins">ins</a></code> and <code><a
   href="#del">del</a></code> elements</h4>

  <p>The <dfn id=cite3 title=attr-mod-cite><code>cite</code></dfn> attribute
   may be used to specify a URI that explains the change. When that document
   is long, for instance the minutes of a meeting, authors are encouraged to
   include a fragment identifier pointing to the specific part of that
   document that discusses the change.

  <p>If the <code title=attr-mod-cite><a href="#cite3">cite</a></code>
   attribute is present, it must be a URI (or IRI) that explains the change.
   User agents should allow users to follow such citation links.

  <p>The <dfn id=datetime1
   title=attr-mod-datetime><code>datetime</code></dfn> attribute may be used
   to specify the time and date of the change.

  <p>If present, the <code title=attr-mod-datetime><a
   href="#datetime1">datetime</a></code> attribute must be a <a
   href="#valid5">valid datetime</a> value.

  <p>User agents must parse the <code title=attr-mod-datetime><a
   href="#datetime1">datetime</a></code> attribute according to the <a
   href="#datetime-parser">parse a string as a datetime value</a> algorithm.
   If that doesn't return a time, then the modification has no associated
   timestamp (the value is non-conforming; it is not a <a
   href="#valid5">valid datetime</a>). Otherwise, the modification is marked
   as having been made at the given datetime. User agents should use the
   associated timezone information to determine which timezone to present the
   given datetime in.

  <p>The <code><a href="#ins">ins</a></code> and <code><a
   href="#del">del</a></code> elements must implement the <code><a
   href="#htmlmodelement">HTMLModElement</a></code> interface:

  <pre
   class=idl>interface <dfn id=htmlmodelement>HTMLModElement</dfn> : <a href="#htmlelement">HTMLElement</a> {
           attribute DOMString <a href="#cite4" title=dom-mod-cite>cite</a>;
           attribute DOMString <a href="#datetime2" title=dom-mod-datetime>dateTime</a>;
};</pre>

  <p>The <dfn id=cite4 title=dom-mod-cite><code>cite</code></dfn> DOM
   attribute must reflect the element's ><code title=attr-mod-cite><a
   href="#cite3">cite</a></code> content attribute. The <dfn id=datetime2
   title=dom-mod-datetime><code>dateTime</code></dfn> DOM attribute must
   reflect the element's <code title="">datetime</code> content attribute.

  <h3 id=embedded><span class=secno>3.14. </span>Embedded content</h3>

  <h4 id=the-figure><span class=secno>3.14.1. </span>The <dfn
   id=figure><code>figure</code></dfn> element</h4>

  <p><a href="#block-level0" title="block-level elements">Block-level
   element</a>.

  <dl class=element>
   <dt>Contexts in which this element may be used:

   <dd>Where <a href="#block-level0">block-level elements</a> are expected.

   <dt>Content model:

   <dd>In any order, exactly one <code><a href="#legend">legend</a></code>
    element, and exactly one <a href="#embedded0">embedded content</a>
    element.

   <dt>Element-specific attributes:

   <dd>None.

   <dt>DOM interface:

   <dd>No difference from <code><a
    href="#htmlelement">HTMLElement</a></code>.
  </dl>

  <p>The <code><a href="#figure">figure</a></code> element represents a <a
   href="#paragraph">paragraph</a> consisting of embedded content and a
   caption.

  <p>The first <a href="#embedded0">embedded content</a> element child of the
   <code><a href="#figure">figure</a></code> element, if any, is the
   paragraph's content.

  <p>The first <code><a href="#legend">legend</a></code> element child of the
   element, if any, represents the caption of the embedded content. If there
   is no child <code><a href="#legend">legend</a></code> element, then there
   is no caption.

  <p>If the embedded content cannot be used, then, for the purposes of
   establishing what the <code><a href="#figure">figure</a></code> element
   represents:

  <dl class=switch>
   <dt>If the embedded content's <a href="#fallback">fallback content</a> is
    a single <a href="#embedded0">embedded content</a> element

   <dd>The <code><a href="#figure">figure</a></code> element must be treated
    as if that <a href="#embedded0">embedded content</a> element was the
    <code><a href="#figure">figure</a></code> element's embedded content. (If
    that embedded content can't be used either, then this processing must be
    done again, with the new embedded content's <a href="#fallback">fallback
    content</a>.)

   <dt>If the embedded content's fallback is nothing

   <dd>The entire <code><a href="#figure">figure</a></code> element
    (including the caption, if any) must be ignored.

   <dt>If the embedded content's fallback is <a
    href="#inline-level0">inline-level content</a>

   <dd>The entire <code><a href="#figure">figure</a></code> element
    (including the caption, if any) must be treated as being a single <a
    href="#paragraph">paragraph</a> with that <a
    href="#inline-level0">inline-level content</a> as its content.

   <dt>Otherwise

   <dd>The entire <code><a href="#figure">figure</a></code> element
    (including the caption, if any) must be treated as being replaced by that
    fallback content.
  </dl>

  <h4 id=the-img><span class=secno>3.14.2. </span>The <dfn
   id=img><code>img</code></dfn> element</h4>

  <p><a href="#strictly" title="Strictly inline-level content">Strictly
   inline-level</a> <a href="#embedded0">embedded content</a>.

  <dl class=element>
   <dt>Contexts in which this element may be used:

   <dd>As the only <a href="#embedded0">embedded content</a> child of a
    <code><a href="#figure">figure</a></code> element.

   <dd>Where <a href="#strictly">strictly inline-level content</a> is
    allowed.

   <dt>Content model:

   <dd>Empty.

   <dt>Element-specific attributes:

   <dd><code title=attr-img-alt><a href="#alt">alt</a></code> (required)

   <dd><code title=attr-img-src><a href="#src">src</a></code> (required)

   <dd><code title=attr-hyperlink-usemap><a href="#usemap1">usemap</a></code>

   <dd><code title=attr-img-ismap><a href="#ismap">ismap</a></code> (but only
    if one of the ancestor elements is an <code><a href="#a">a</a></code>
    element)

   <dd><code title=attr-img-height><a href="#height">height</a></code>

   <dd><code title=attr-img-width><a href="#width">width</a></code>

   <dt>DOM interface:

   <dd>
    <pre
     class=idl>interface <dfn id=htmlimageelement>HTMLImageElement</dfn> : <a href="#htmlelement">HTMLElement</a> {
           attribute DOMString <a href="#alt0" title=dom-img-alt>alt</a>;
           attribute DOMString <a href="#src0" title=dom-img-src>src</a>;
           attribute DOMString <a href="#usemap" title=dom-img-useMap>useMap</a>;
           attribute boolean <a href="#ismap0" title=dom-img-isMap>isMap</a>;
           attribute long <a href="#height0" title=dom-img-height>height</a>;
           attribute long <a href="#width0" title=dom-img-width>width</a>;
  readonly attribute boolean <a href="#complete" title=dom-img-complete>complete</a>;
};</pre>

    <p class=note>An instance of <code><a
     href="#htmlimageelement">HTMLImageElement</a></code> can be obtained
     using the <code title=dom-image><a href="#image0">Image</a></code>
     constructor.</p>
  </dl>

  <p>The <code><a href="#img">img</a></code> element represents a piece of
   text with an alternate graphical representation. The text is given by the
   <dfn id=alt title=attr-img-alt><code>alt</code></dfn> attribute, which
   must be present, and the URI to the graphical representation of that text
   is given in the <dfn id=src title=attr-img-src><code>src</code></dfn>
   attribute, which must also be present.

  <p>The image given by the <code title=attr-img-src><a
   href="#src">src</a></code> attribute is the embedded content, and the
   value of the <code title=attr-img-alt><a href="#alt">alt</a></code>
   attribute is the <code><a href="#img">img</a></code> element's <a
   href="#fallback">fallback content</a>.

  <p>When the <code title=attr-img-alt><a href="#alt">alt</a></code>
   attribute's value is the empty string, the image supplements the
   surrounding content. In such cases, the image could be omitted without
   affecting the meaning of the document.

  <p>If the <code title=attr-img-alt><a href="#alt">alt</a></code> attribute
   is omitted, user agents must treat the element as if it had an <code
   title=attr-img-alt><a href="#alt">alt</a></code> attribute set to the
   empty string.

  <p>The <code title=attr-img-alt><a href="#alt">alt</a></code> attribute
   does not represent advisory information. User agents must not present the
   contents of the <code title=attr-img-alt><a href="#alt">alt</a></code>
   attribute in the same way as content of the <code title=attr-title><a
   href="#title">title</a></code> attribute.

  <p class=big-issue>Guidelines on writing "alt" text here.</p>
  <!-- http://www.cs.tut.fi/~jkorpela/html/alt.html -->

  <p>The <code title=attr-img-src><a href="#src">src</a></code> attribute
   must contain a URI (or IRI). If the <code title=attr-img-src><a
   href="#src">src</a></code> attribute is omitted, there is no alternative
   image representation.

  <p>When the <code title=attr-img-src><a href="#src">src</a></code>
   attribute is set, the user agent must immediately begin to download the
   specified
   resource<!-- XXX xref what fetching means, how to resolve URIs in
  attributes (including those not in the DOM) -->,
   unless the user agent cannot support images, or its support for images has
   been disabled.

  <p>The download of the image must <a href="#delays">delay the <code
   title=event-load>load</code> event</a>.

  <p>Once the download has completed, if the image is a valid image, the user
   agent must <a href="#firing4">fire a <code title=event-load>load</code>
   event</a> on the <code><a href="#img">img</a></code> element. If the
   download fails or it completes but the image is not a valid or supported
   image, the user agent must <a href="#firing5">fire an <code
   title=event-error>error</code> event</a> on the <code><a
   href="#img">img</a></code> element.

  <p>The remote server's response metadata (e.g. an HTTP 404 status code, or
   <a href="#content-type8" title=Content-Type>associated Content-Type
   headers</a>) must be ignored when determining whether the resource
   obtained is a valid image or not.

  <p class=note>This allows servers to return images with error responses.

  <p>User agents must not support non-image resources with the <code><a
   href="#img">img</a></code> element.

  <p>The <code title=attr-hyperlink-usemap><a
   href="#usemap1">usemap</a></code> attribute, if present, can indicate that
   the image has an associated <a href="#image">image map</a>.

  <p>The <dfn id=ismap title=attr-img-ismap><code>ismap</code></dfn>
   attribute, when used on an element that is a descendant of an <code><a
   href="#a">a</a></code> element with an <code title=attr-hyperlink-href><a
   href="#href6">href</a></code> attribute, indicates by its presence that
   the element provides access to a server-side image map. This affects how
   events are handled on the corresponding <code><a href="#a">a</a></code>
   element.

  <p>The <code title=attr-img-ismap><a href="#ismap">ismap</a></code>
   attribute is a <a href="#boolean0">boolean attribute</a>. The attribute
   must not be specified on an element that does not have an ancestor
   <code><a href="#a">a</a></code> element.

  <p>The <dfn id=height title=attr-img-height><code>height</code></dfn> and
   <dfn id=width title=attr-img-width><code>width</code></dfn> attributes
   give the preferred rendered dimensions of the image if the image is to be
   shown in a visual medium.

  <p class=big-issue>Should we require the dimensions to be correct? Should
   we disallow percentages?

  <p>The values of the <code title=attr-img-height><a
   href="#height">height</a></code> and <code title=attr-img-width><a
   href="#width">width</a></code> attributes must be either <a href="#valid"
   title="valid non-negative integer">valid non-negative integers</a> or <a
   href="#valid3" title="valid non-negative percentage">valid non-negative
   percentages</a>.

  <p>To parse the attributes, user agents must use the <a
   href="#rules2">rules for parsing dimension values</a>. This will return
   either an integer length, a percentage value, or nothing. When one of
   these attributes has no value, it must be
   <span>ignored</span><!-- XXX xref -->.

  <p>The user agent requirements for processing the values obtained from
   parsing these attributes are described <a href="#sizing" title="sizing of
   embedded content">in the rendering section</a><!-- XXX xref
  -->.

  <p>The <code><a href="#img">img</a></code> element must be empty.</p>
  <!-- contents
  should be ignored for rendering but not for semantics,
  e.g. <script>, <input>, etc. -->

  <p>The DOM attributes <dfn id=alt0
   title=dom-img-alt><code>alt</code></dfn>, <dfn id=src0
   title=dom-img-src><code>src</code></dfn>, <dfn id=usemap
   title=dom-img-useMap><code>useMap</code></dfn>, and <dfn id=ismap0
   title=dom-img-isMap><code>isMap</code></dfn> each must <a
   href="#reflect">reflect</a> the respective content attributes of the same
   name.

  <p>The DOM attributes <dfn id=height0
   title=dom-img-height><code>height</code></dfn> and <dfn id=width0
   title=dom-img-width><code>width</code></dfn> must return the rendered
   height and width of the image, in CSS pixels, if the image is being
   rendered, and is being rendered to a visual medium, or 0 otherwise. <a
   href="#refsCSS21">[CSS21]</a>

  <p>The DOM attribute <dfn id=complete
   title=dom-img-complete><code>complete</code></dfn> must return true if the
   user agent has downloaded the image specified in the <code
   title=attr-img-src><a href="#src">src</a></code> attribute, and it is a
   valid image, and false otherwise.

  <h4 id=the-iframe><span class=secno>3.14.3. </span>The <dfn
   id=iframe><code>iframe</code></dfn> element</h4>

  <p><a href="#strictly" title="Strictly inline-level content">Strictly
   inline-level</a> <a href="#embedded0">embedded content</a>.

  <dl class=element>
   <dt>Contexts in which this element may be used:

   <dd>As the only <a href="#embedded0">embedded content</a> child of a
    <code><a href="#figure">figure</a></code> element.

   <dd>Where <a href="#strictly">strictly inline-level content</a> is
    allowed.

   <dt>Content model:

   <dd>Text (for details, see prose).

   <dt>Element-specific attributes:

   <dd><code title=attr-iframe-src><a href="#src1">src</a></code>

   <dt>DOM interface:

   <dd>
    <pre
     class=idl>interface <dfn id=htmliframeelement>HTMLIFrameElement</dfn> : <a href="#htmlelement">HTMLElement</a> {
           attribute DOMString <a href="#src2" title=dom-iframe-src>src</a>;<!--
  readonly attribute Document <span title="dom-iframe-contentDocument">contentDocument</span>;
  readonly attribute <span>Window</span> <span title="dom-iframe-contentWindow">contentWindow</span>;-->
};</pre>

    <p>Objects implementing the <code><a
     href="#htmliframeelement">HTMLIFrameElement</a></code> interface must
     also implement the <code>EmbeddingElement</code> interface defined in
     the Window Object specification. <a href="#refsWINDOW">[WINDOW]</a></p>
    <!-- XXX -->
  </dl>

  <p>The <code><a href="#iframe">iframe</a></code> element introduces a new
   nested <a href="#browsing0">browsing context</a>.

  <p>The <dfn id=src1 title=attr-iframe-src><code>src</code></dfn> attribute,
   if present, must be a URI (or IRI) to a page that the nested <a
   href="#browsing0">browsing context</a> is to contain. When the browsing
   context is created, if the attribute is present, the user agent must <a
   href="#navigate">navigate</a> this browsing context to the given URI, with
   <a href="#replacement">replacement enabled</a>. If the user <a
   href="#navigate" title=navigate>navigates</a> away from this page, the
   <code><a href="#iframe">iframe</a></code>'s corresponding <code><a
   href="#window">Window</a></code> object will reference new
   <code>Document</code> objects, but the <code title=attr-iframe-src><a
   href="#src1">src</a></code> attribute will not change.

  <p>Whenever the <code title=attr-iframe-src><a href="#src1">src</a></code>
   attribute is set, the nested <a href="#browsing0">browsing context</a>
   must be <a href="#navigate" title=navigate>navigated</a> to the given URI.

  <p>If the <code title=attr-iframe-src><a href="#src1">src</a></code>
   attribute is not set when the element is created, the browsing context
   will remain at the initial <code>about:blank</code> page.

  <p>When content loads in an <code><a href="#iframe">iframe</a></code>,
   after any <code title=event-load><a href="#load0">load</a></code> events
   are fired within the content itself, the user agent must <a
   href="#firing4">fire a <code title=event-load>load</code> event</a> at the
   <code><a href="#iframe">iframe</a></code> element. When content fails to
   load (e.g. due to a network error), then the user agent must <a
   href="#firing5">fire an <code title=event-error>error</code> event</a> at
   the element instead.

  <p>When there is an active parser in the <code><a
   href="#iframe">iframe</a></code>, and when anything in the <code><a
   href="#iframe">iframe</a></code> that is <a href="#delays" title="delay
   the load event">delaying the <code title=event-load>load</code> event</a>
   in the <code><a href="#iframe">iframe</a></code>'s <a
   href="#browsing0">browsing context</a>, the <code><a
   href="#iframe">iframe</a></code> must <a href="#delays">delay the <code
   title=event-load>load</code> event</a>.

  <p class=note>If, during the handling of the <code title=event-load><a
   href="#load0">load</a></code> event, the <a href="#browsing0">browsing
   context</a> in the <code><a href="#iframe">iframe</a></code> is again <a
   href="#navigate" title=navigate>navigated</a>, that will further <a
   href="#delays">delay the <code title=event-load>load</code> event</a>.

  <p>An <code><a href="#iframe">iframe</a></code> element never has <a
   href="#fallback">fallback content</a>, as it will always create a nested
   <a href="#browsing0">browsing context</a>, regardless of whether the
   specified initial contents are successfully used.

  <p><code><a href="#iframe">iframe</a></code> elements may contain any text.
   <code><a href="#iframe">iframe</a></code> elements must not contain
   element nodes. Descendants of <code><a href="#iframe">iframe</a></code>
   elements represent nothing. (In legacy user agents that do not support
   <code><a href="#iframe">iframe</a></code> elements, the contents would be
   parsed as markup that could act as fallback content.)

  <p class=big-issue>restrictions for what that text must be?

  <p class=note>The <a href="#html-0">HTML parser</a> treats markup inside
   <code><a href="#iframe">iframe</a></code> elements as text.

  <p>The DOM attribute <dfn id=src2
   title=dom-iframe-src><code>src</code></dfn> must <a
   href="#reflect">reflect</a> the content attribute of the same name.

  <h4 id=the-embed><span class=secno>3.14.4. </span>The <dfn
   id=embed><code>embed</code></dfn> element</h4>

  <p><a href="#strictly" title="Strictly inline-level content">Strictly
   inline-level</a> <a href="#embedded0">embedded content</a>.

  <dl class=element>
   <dt>Contexts in which this element may be used:

   <dd>As the only <a href="#embedded0">embedded content</a> child of a
    <code><a href="#figure">figure</a></code> element.

   <dd>Where <a href="#strictly">strictly inline-level content</a> is
    allowed.

   <dt>Content model:

   <dd>Empty.

   <dt>Element-specific attributes:

   <dd><code title=attr-embed-src><a href="#src3">src</a></code> (required)

   <dd><code title=attr-embed-type><a href="#type4">type</a></code>

   <dd><code title=attr-embed-height>height</code>

   <dd><code title=attr-embed-width>width</code>

   <dd>Any other attribute that has no namespace (see prose).

   <dt>DOM interface:

   <dd>
    <pre
     class=idl>interface <dfn id=htmlembedelement>HTMLEmbedElement</dfn> : <a href="#htmlelement">HTMLElement</a> {
           attribute DOMString <a href="#src4" title=dom-embed-src>src</a>;
           attribute DOMString <a href="#type5" title=dom-embed-type>type</a>;
           attribute long <a href="#height1" title=dom-embed-height>height</a>;
           attribute long <a href="#width1" title=dom-embed-width>width</a>;
};</pre>

    <p>Depending on the type of content instantiated by the <code><a
     href="#embed">embed</a></code> element, the node may also support other
     interfaces.</p>
  </dl>

  <p>The <code><a href="#embed">embed</a></code> element represents an
   integration point for an external (typically non-HTML) application or
   interactive content.

  <p>The <dfn id=src3 title=attr-embed-src><code>src</code></dfn> attribute
   gives the address of the resource being embedded. The attribute must be
   present and contain a URI (or IRI).

  <p>If the <code title=attr-embed-src><a href="#src3">src</a></code>
   attribute is missing, then the <code><a href="#embed">embed</a></code>
   element must be ignored.

  <p>When the <code title=attr-embed-src><a href="#src3">src</a></code>
   attribute is set, user agents are expected to find an appropriate handler
   for the specified resource, based on the <a href="#type-of"
   title=concept-embed-type>content's type</a>, and hand that handler the
   content of the resource. If the handler supports a scriptable interface,
   the <code><a href="#htmlembedelement">HTMLEmbedElement</a></code> object
   representing the element should expose that interfaces.

  <p>The download of the resource must <a href="#delays">delay the <code
   title=event-load>load</code> event</a>.

  <p>The user agent should pass the names and values of all the attributes of
   the <code><a href="#embed">embed</a></code> element that have no namespace
   to the handler used. Any (namespace-less) attribute may be specified on
   the <code><a href="#embed">embed</a></code> element.</p>
  <!-- duplicates what's in <object> section below -->

  <p class=note>This specification does not define a mechanism for
   interacting with third-party handlers, as it is expected to be
   user-agent-specific. Some UAs might opt to support a plugin mechanism such
   as the Netscape Plugin API; others may use remote content convertors or
   have built-in support for certain types. <a href="#refsNPAPI">[NPAPI]</a>

  <p>The <code><a href="#embed">embed</a></code> element has no <a
   href="#fallback">fallback content</a>. If the user agent can't display the
   specified resource, e.g. because the given type is not supported, then the
   user agent must use a default handler for the content. (This default could
   be as simple as saying "Unsupported Format", of course.)

  <p>The <dfn id=type4 title=attr-embed-type><code>type</code></dfn>
   attribute, if present, gives the MIME type of the linked resource. The
   value must be a valid MIME type, optionally with parameters. <a
   href="#refsRFC2046">[RFC2046]</a>

  <p>The <dfn id=type-of title=concept-embed-type>type of the content</dfn>
   being embedded is defined as follows:

  <ol>
   <li>If the element has a <code title=attr-embed-type><a
    href="#type4">type</a></code> attribute, then the value of the <code
    title=attr-embed-type><a href="#type4">type</a></code> attribute is the
    <span>content's type</span>.

   <li>Otherwise, if the specified resource has <a href="#content-type8"
    title=Content-Type>explicit Content-Type metadata</a>, then that is the
    <span>content's type</span>.

   <li>Otherwise, the content has no type and there can be no appropriate
    handler for it.
  </ol>

  <p class=big-issue>Should we instead say that the content-sniffing that
   we're going to define for top-level browsing contexts should apply here?

  <p class=big-issue>Should we require the type attribute to match the server
   information?

  <p class=big-issue>We should say that 404s, etc, don't affect whether the
   resource is used or not. Not sure how to say it here though.

  <p>Browsers should take extreme care when interacting with external content
   intended for third-party renderers. When third-party software is run with
   the same privileges as the user agent itself, vulnerabilities in the
   third-party software become as dangerous as those in the user agent.

  <p class=big-issue>height/width

  <p>The DOM attributes <dfn id=src4
   title=dom-embed-src><code>src</code></dfn> and <dfn id=type5
   title=dom-embed-type><code>type</code></dfn> each must <a
   href="#reflect">reflect</a> the respective content attributes of the same
   name.

  <p>The DOM attributes <dfn id=height1
   title=dom-embed-height><code>height</code></dfn> and <dfn id=width1
   title=dom-embed-width><code>width</code></dfn> must return the rendered
   height and width of the image, in CSS pixels, if the image is being
   rendered, and is being rendered to a visual medium, or 0 otherwise. <a
   href="#refsCSS21">[CSS21]</a>

  <h4 id=the-object><span class=secno>3.14.5. </span>The <dfn
   id=object><code>object</code></dfn> element</h4>

  <p><a href="#strictly" title="Strictly inline-level content">Strictly
   inline-level</a> <a href="#embedded0">embedded content</a>.

  <dl class=element>
   <dt>Contexts in which this element may be used:

   <dd>As the only <a href="#embedded0">embedded content</a> child of a
    <code><a href="#figure">figure</a></code> element.

   <dd>Where <a href="#strictly">strictly inline-level content</a> is
    allowed.

   <dt>Content model:

   <dd>When used as the child of a <code><a href="#figure">figure</a></code>
    element, or, when used as a <em><code><a href="#figure">figure</a></code>
    fallback <code><a href="#object">object</a></code></em>: Zero or more
    <code><a href="#param">param</a></code> elements, followed by either zero
    or more <a href="#block-level0">block-level elements</a> or a single
    <code><a href="#object">object</a></code> element, which is then
    considered to be a <em><code><a href="#figure">figure</a></code> fallback
    <code><a href="#object">object</a></code></em>.

   <dd>Otherwise: Zero or more <code><a href="#param">param</a></code>
    elements, followed by <a href="#inline-level0">inline-level content</a>.

   <dt>Element-specific attributes:

   <dd><code title=attr-object-data><a href="#data">data</a></code> (required
    if <code title=attr-object-type><a href="#type6">type</a></code> is not
    given)

   <dd><code title=attr-object-type><a href="#type6">type</a></code>
    (required if <code title=attr-object-data><a href="#data">data</a></code>
    is not given)

   <dd><code title=attr-hyperlink-usemap><a href="#usemap1">usemap</a></code>

   <dd><code title=attr-object-height>height</code>

   <dd><code title=attr-object-width>width</code>

   <dt>DOM interface:

   <dd>
    <pre
     class=idl>interface <dfn id=htmlobjectelement>HTMLObjectElement</dfn> : <a href="#htmlelement">HTMLElement</a> {
           attribute DOMString <a href="#data0" title=dom-object-data>data</a>;
           attribute DOMString <a href="#type7" title=dom-object-type>type</a>;
           attribute DOMString <a href="#usemap0" title=dom-object-useMap>useMap</a>;
           attribute long <a href="#height2" title=dom-object-height>height</a>;
           attribute long <a href="#width2" title=dom-object-width>width</a>;<!--
  readonly attribute Document <span title="dom-object-contentDocument">contentDocument</span>;
  readonly attribute <span>Window</span> <span title="dom-object-contentWindow">contentWindow</span>;-->
};</pre>

    <p>Objects implementing the <code><a
     href="#htmlobjectelement">HTMLObjectElement</a></code> interface must
     also implement the <code>EmbeddingElement</code> interface defined in
     the Window Object specification. <a href="#refsWINDOW">[WINDOW]</a></p>

    <p>Depending on the type of content instantiated by the <code><a
     href="#object">object</a></code> element, the node may also support
     other interfaces.</p>
  </dl>

  <p class=big-issue>Shouldn't allow inline-level content to be the content
   model when the parent's content model is strictly inline only.

  <p>The <code><a href="#object">object</a></code> element can represent an
   external resource, which, depending on the type of the resource, will
   either be treated as an image, as a nested <a href="#browsing0">browsing
   context</a>, or as an external resource to be processed by a third-party
   software package.

  <p>The <dfn id=data title=attr-object-data><code>data</code></dfn>
   attribute, if present, specifies the address of the resource. If present,
   the attribute must be a URI (or IRI).

  <p>The <dfn id=type6 title=attr-object-type><code>type</code></dfn>
   attribute, if present, specifies the type of the resource. If present, the
   attribute must be a valid MIME type, optionally with parameters. <a
   href="#refsRFC2046">[RFC2046]</a>

  <p>One or both of the <code title=attr-object-data><a
   href="#data">data</a></code> and <code title=attr-object-type><a
   href="#type6">type</a></code> attributes must be present.

  <p>Whenever the <code title=attr-object-data><a
   href="#data">data</a></code> attribute changes, or, if the <code
   title=attr-object-data><a href="#data">data</a></code> attribute is not
   present, whenever the <code title=attr-object-type><a
   href="#type6">type</a></code> attribute changes, the user agent must
   follow the following steps to determine what the <code><a
   href="#object">object</a></code> element represents:

  <ol>
   <li>
    <p>If the <code title=attr-object-data><a href="#data">data</a></code>
     attribute is present, then:</p>

    <ol>
     <li>
      <p>Begin a load for the resource.</p>
      <!-- XXX define that
      --><!-- XXX xref -->
      <p>The download of the resource must <a href="#delays">delay the <code
       title=event-load>load</code> event</a>.</p>

     <li>
      <p>If the resource is not yet available (e.g. because the resource was
       not available in the cache, so that loading the resource required
       making a request over the network), then jump to step 3 in the overall
       set of steps (fallback). When the resource becomes available, or if
       the load fails, restart this algorithm from this step. Resources can
       load incrementally; user agents may opt to consider a resource
       "available" whenever enough data has been obtained to begin processing
       the resource.

     <li>
      <p>If the load failed (e.g. DNS error), <a href="#firing5">fire an
       <code title=event-error>error</code> event</a> at the element, then
       jump to step 3 in the overall set of steps (fallback).

     <li>
      <p>Determine the <em>resource type</em>, as follows:</p>

      <p class=big-issue>This says to trust the type. Should we instead use
       the same mechanism as for browsing contexts?</p>

      <dl class=switch>
       <dt>If the resource has <a href="#content-type8"
        title=Content-Type>associated Content-Type metadata</a>

       <dd>The type is the type specified in <a href="#content-type8"
        title=Content-Type>the resource's Content-Type metadata</a>.

       <dt>Otherwise, if the <code title=attr-object-type><a
        href="#type6">type</a></code> attribute is present

       <dd>The type is the type specified in the <code
        title=attr-object-type><a href="#type6">type</a></code> attribute.

       <dt>Otherwise, there is no explicit type information

       <dd>The type is the <span title="sniffed type of a resource">sniffed
        type of the resource</span>.
      </dl>

     <li>
      <p>Handle the content as given by the first of the following cases that
       matches:</p>

      <dl class=switch>
       <dt>If the resource requires a special handler (e.g. a plugin)

       <dd>
        <p>The user agent should find an appropriate handler for the
         specified resource, based on the <em>resource type</em> found in the
         previous step, and pass the content of the resource to that handler.
         If the handler supports a scriptable interface, the <code><a
         href="#htmlobjectelement">HTMLObjectElement</a></code> object
         representing the element should expose that interface. The handler
         is not a nested <a href="#browsing0">browsing context</a>. If no
         appropriate handler can be found, then jump to step 3 in the overall
         set of steps (fallback).</p>

        <p>The user agent should pass the names and values of all the <span
         title=concept-param-parameter>parameters</span> given by <code><a
         href="#param">param</a></code> elements that are children of the
         <code><a href="#object">object</a></code> element to the handler
         used.</p>
        <!-- duplicates what's in <embed> section above -->
        <p class=note>This specification does not define a mechanism for
         interacting with third-party handlers, as it is expected to be
         user-agent-specific. Some UAs might opt to support a plugin
         mechanism such as the Netscape Plugin API; others may use remote
         content convertors or have built-in support for certain types. <a
         href="#refsNPAPI">[NPAPI]</a></p>

        <p class=big-issue>this doesn't completely duplicate the navigation
         section, since it handles &lt;param>, etc, but surely some work
         should be done to work with it</p>

       <dt>If the type of the resource is an <span>XML MIME
        type</span><!-- XXX xref -->

       <dt>If the type of the resource is HTML

       <dt>If the type of the resource does not start with
        "<code>image/</code>"

       <dd>
        <p>The <code><a href="#object">object</a></code> element must be
         associated with a nested <a href="#browsing0">browsing context</a>,
         if it does not already have one. The element's nested <a
         href="#browsing0">browsing context</a> must then be <a
         href="#navigate" title=navigate>navigated</a> to the given resource,
         with <a href="#replacement">replacement enabled</a>. (The <code
         title=attr-object-data><a href="#data">data</a></code> attribute of
         the <code><a href="#object">object</a></code> element doesn't get
         updated if the browsing context gets further navigated to other
         locations.)</p>

        <p class=big-issue>navigation might end up treating it as something
         else, because it can do sniffing. how should we handle that?</p>

       <dt>If the resource is a supported image format, and support for
        images has not been disabled

       <dd>
        <p>The <code><a href="#object">object</a></code> element represents
         the specified image. The image is not a nested <a
         href="#browsing0">browsing context</a>.</p>

        <p class=big-issue>shouldn't we use the image-sniffing stuff here?</p>

       <dt>Otherwise

       <dd>
        <p>The <code><a href="#object">object</a></code> element represents
         the specified image, but the image cannot be shown. Jump to step 3
         below in the overall set of steps (fallback).</p>
      </dl>

     <li>
      <p>The element's contents are not part of what the <code><a
       href="#object">object</a></code> element represents.</p>

     <li>
      <p>Once the resource is completely loaded, <a href="#firing4">fire a
       <code title=event-load>load</code> event</a> at the element.
     </li>
     <!-- XXX ordering of events (like with iframe)
     -->
    </ol>

   <li>
    <p>If the <code title=attr-object-data><a href="#data">data</a></code>
     attribute is absent but the <code title=attr-object-type><a
     href="#type6">type</a></code> attribute is present, and if the user
     agent can find a handler suitable according to the value of the <code
     title=attr-object-type><a href="#type6">type</a></code> attribute, then
     that handler should be used. If the handler supports a scriptable
     interface, the <code><a
     href="#htmlobjectelement">HTMLObjectElement</a></code> object
     representing the element should expose that interface. The handler is
     not a nested <a href="#browsing0">browsing context</a>. If no suitable
     handler can be found, jump to the next step (fallback).

   <li>
    <p>(Fallback.) The <code><a href="#object">object</a></code> element
     doesn't represent anything except what the element's contents represent,
     ignoring any leading <code><a href="#param">param</a></code> element
     children. This is the element's <a href="#fallback">fallback
     content</a>.
  </ol>

  <p>In the absence of other factors (such as style sheets), user agents must
   show the user what the <code><a href="#object">object</a></code> element
   represents. Thus, the contents of <code><a
   href="#object">object</a></code> elements act as <a
   href="#fallback">fallback content</a>, to be used only when referenced
   resources can't be shown (e.g. because it returned a 404 error). This
   allows multiple <code><a href="#object">object</a></code> elements to be
   nested inside each other, targeting multiple user agents with different
   capabilities, with the user agent picking the best one it supports.

  <p>The <code title=attr-hyperlink-usemap><a
   href="#usemap1">usemap</a></code> attribute, if present while the <code><a
   href="#object">object</a></code> element represents an image, can indicate
   that the object has an associated <a href="#image">image map</a>. The
   attribute must be ignored if the <code><a href="#object">object</a></code>
   element doesn't represent an image.

  <p class=big-issue>height/width

  <p>The DOM attributes <dfn id=data0
   title=dom-object-data><code>data</code></dfn>, <dfn id=type7
   title=dom-object-type><code>type</code></dfn>, <dfn id=usemap0
   title=dom-object-useMap><code>useMap</code></dfn>, <dfn id=height2
   title=dom-object-height><code>height</code></dfn>, and <dfn id=width2
   title=dom-object-width><code>width</code></dfn> each must <a
   href="#reflect">reflect</a> the respective content attributes of the same
   name.

  <h4 id=the-param><span class=secno>3.14.6. </span>The <dfn
   id=param><code>param</code></dfn> element</h4>
  <!-- no type -->

  <dl class=element>
   <dt>Contexts in which this element may be used:

   <dd>As a child of an <code><a href="#object">object</a></code> element,
    before any content other than <code><a href="#param">param</a></code>
    elements.

   <dt>Content model:

   <dd>Empty.

   <dt>Element-specific attributes:

   <dd><code title=attr-param-name><a href="#name1">name</a></code>
    (required)

   <dd><code title=attr-param-value><a href="#value5">value</a></code>
    (required)

   <dt>DOM interface:

   <dd>
    <pre
     class=idl>interface <dfn id=htmlparamelement>HTMLParamElement</dfn> : <a href="#htmlelement">HTMLElement</a> {
           attribute DOMString <a href="#name2" title=dom-param-name>name</a>;
           attribute DOMString <a href="#value6" title=dom-param-value>value</a>;
};</pre>
  </dl>

  <p>The <code><a href="#param">param</a></code> element defines parameters
   for handlers invoked by <code><a href="#object">object</a></code>
   elements.

  <p>The <dfn id=name1 title=attr-param-name><code>name</code></dfn>
   attribute gives the name of the parameter.

  <p>The <dfn id=value5 title=attr-param-value><code>value</code></dfn>
   attribute gives the value of the parameter.

  <p>Both attributes must be present. They may have any value.

  <p>If both attributes are present, and if the parent element of the
   <code><a href="#param">param</a></code> is an <code><a
   href="#object">object</a></code> element, then the element defines a <dfn
   id=parameter title=concept-param-parameters>parameter</dfn> with the given
   name/value pair.

  <p>The DOM attributes <dfn id=name2
   title=dom-param-name><code>name</code></dfn> and <dfn id=value6
   title=dom-param-value><code>value</code></dfn> must both <a
   href="#reflect">reflect</a> the respective content attributes of the same
   name.

  <h4 id=video><span class=secno>3.14.7. </span>The <dfn
   id=video1><code>video</code></dfn> element</h4>

  <p><a href="#semi-transparent">Semi-transparent</a> <a href="#strictly"
   title="Strictly inline-level content">strictly inline-level</a> <a
   href="#embedded0">embedded content</a>.

  <dl class=element>
   <dt>Contexts in which this element may be used:

   <dd>As the only <a href="#embedded0">embedded content</a> child of a
    <code><a href="#figure">figure</a></code> element.

   <dd>Where <a href="#strictly">strictly inline-level content</a> is
    allowed.

   <dt>Content model:

   <dd>If the element has a <code title=attr-media-src><a
    href="#src5">src</a></code> attribute: <a
    href="#transparent0">transparent</a>.

   <dd>If the element does not have a <code title=attr-media-src><a
    href="#src5">src</a></code> attribute: one or more <code><a
    href="#source">source</a></code> elements, then, <a
    href="#transparent0">transparent</a>.

   <dt>Element-specific attributes:

   <dd><code title=attr-media-src><a href="#src5">src</a></code>

   <dd><code title=attr-media-autoplay><a
    href="#autoplay">autoplay</a></code>

   <dd><code title=attr-media-start><a href="#start2">start</a></code>

   <dd><code title=attr-media-loopstart><a
    href="#loopstart">loopstart</a></code>

   <dd><code title=attr-media-loopend><a href="#loopend">loopend</a></code>

   <dd><code title=attr-media-end><a href="#end">end</a></code>

   <dd><code title=attr-media-loopcount><a
    href="#loopcount">loopcount</a></code>

   <dd><code title=attr-media-controls><a
    href="#controls">controls</a></code>

   <dt>DOM interface:

   <dd>
    <pre
     class=idl>interface <dfn id=htmlvideoelement>HTMLVideoElement</dfn> : <a href="#htmlmediaelement">HTMLMediaElement</a> {
  readonly attribute unsigned long <a href="#videowidth" title=dom-video-videoWidth>videoWidth</a>;
  readonly attribute unsigned long <a href="#videoheight" title=dom-video-videoHeight>videoHeight</a>;
};</pre>
  </dl>
  <!-- XXX request: changing the playback aspect ratio -->
  <!-- XXX request: applying CSS filters -->

  <p>A <code><a href="#video1">video</a></code> element represents a video or
   movie.

  <p>Content may be provided inside the <code><a
   href="#video1">video</a></code> element so that older Web browsers, which
   do not support <code><a href="#video1">video</a></code>, can display text
   to the user informing them of how to access the video contents. User
   agents should not show this fallback content to the user.

  <p>The <code><a href="#video1">video</a></code> element is a <a
   href="#media5">media element</a> whose <a href="#media7">media data</a> is
   ostensibly video data, possibly with associated audio data.

  <p>The <code title=attr-media-src><a href="#src5">src</a></code>, <code
   title=attr-media-autoplay><a href="#autoplay">autoplay</a></code>, <code
   title=attr-media-start><a href="#start2">start</a></code>, <code
   title=attr-media-loopstart><a href="#loopstart">loopstart</a></code>,
   <code title=attr-media-loopend><a href="#loopend">loopend</a></code>,
   <code title=attr-media-end><a href="#end">end</a></code>, <code
   title=attr-media-loopcount><a href="#loopcount">loopcount</a></code>, and
   <code title=attr-media-controls><a href="#controls">controls</a></code>
   attributes are <a href="#media6" title="media element attributes">the
   attributes common to all media elements</a>.

  <p>The <dfn id=videowidth
   title=dom-video-videoWidth><code>videoWidth</code></dfn> DOM attribute
   must return the native width of the video in CSS pixels. The <dfn
   id=videoheight title=dom-video-videoHeight><code>videoHeight</code></dfn>
   DOM attribute must return the native height of the video in CSS pixels. In
   the absence of resolution information, user agents may assume that one
   pixel in the video corresponds to one CSS pixel. If no video data is
   available, then the attributes must return 0.

  <p>When no video data is available (the element's <code
   title=dom-media-networkState><a
   href="#networkstate">networkState</a></code> attribute is either <code
   title=dom-media-EMPTY><a href="#empty">EMPTY</a></code>, <code
   title=dom-media-LOADING><a href="#loading0">LOADING</a></code>, or <code
   title=dom-media-LOADED_METADATA><a
   href="#loadedmetadata">LOADED_METADATA</a></code>), <code><a
   href="#video1">video</a></code> elements represent nothing.

  <p>When a <code><a href="#video1">video</a></code> element is <a
   href="#actively">actively playing</a>, it represents the frame of video at
   the continuously increasing <a href="#current" title="current playback
   position">"current" position</a>. When the <a href="#current">current
   playback position</a> changes such that the last frame rendered is no
   longer the frame corresponding to the <a href="#current">current playback
   position</a> in the video, the new frame must be rendered. Similarly, any
   audio associated with the video must, if played, be played synchronised
   with the <a href="#current">current playback position</a>, at the
   specified <a href="#volume" title=dom-media-volume>volume</a> with the
   specified <a href="#muted" title=dom-media-muted>mute state</a>.

  <p>When a <code><a href="#video1">video</a></code> element is <a
   href="#paused" title=dom-media-paused>paused</a>, the element represents
   the frame of video corresponding to the <a href="#current" title="current
   playback position">current playback position</a>, or, if that is not
   available yet (e.g. because the video is seeking or buffering), the last
   rendered frame of video.

  <p>When a <code><a href="#video1">video</a></code> element is neither <a
   href="#actively">actively playing</a> nor <a href="#paused"
   title=dom-media-paused>paused</a>, the element represents the last frame
   of the video to have been rendered.

  <p class=note>Which frame in a video stream corresponds to a particular
   playback position is defined by the video stream's format.

  <p>Video content should be rendered inside the element's playback area such
   that the video content is shown centered in the playback area at the
   largest possible size that fits completely within it, with the video
   content's aspect ratio being preserved. Thus, if the aspect ratio of the
   playback area does not match the aspect ratio of the video, the video will
   be shown letterboxed. Areas of the element's playback area that do not
   contain the video represent nothing.</p>
  <!-- XXX
   make it an interactive element
   default activation behaviour is to do the play() if paused, pause()
   otherwise
  -->

  <p>User agents should provide controls to enable or disable the display of
   closed captions associated with the video stream, though such features
   should, again, not interfere with the page's normal rendering.

  <p>User agents may allow users to view the video content in manners more
   suitable to the user (e.g. full-screen or in an independent resizable
   window). As for the other user interface features, controls to enable this
   should not interfere with the page's normal rendering unless the user
   agent is <a href="#expose" title="expose a user interface to the
   user">exposing a user interface</a>. In such an independent context,
   however, user agents may make full user interfaces visible, with, e.g.,
   play, pause, seeking, and volume controls, even if the <code
   title=attr-media-controls><a href="#controls">controls</a></code>
   attribute is absent.

  <p>User agents may allow video playback to affect system features that
   could interfere with the user's experience; for example, user agents could
   disable screensavers while video playback is in progress.</p>
  <!-- XXX rendering section should mention that resizing a video
  should in no way interrupt playback -->

  <h5 id=video0><span class=secno>3.14.7.1. </span>Video and audio codecs for
   <code><a href="#video1">video</a></code> elements</h5>

  <p>User agents may support any video and audio codecs and container
   formats.

  <p>User agents should support Ogg Theora video and Ogg Vorbis audio, as
   well as the Ogg container format. <a href="#refsOggTheora">[THEORA]</a> <a
   href="#refsOggVorbis">[VORBIS]</a> <a href="#refsOgg">[OGG]</a></p>
  <!-- (it's not a MUST because some vendors may have legal reasons
  why they can't or won't support it, and there's no point making them
  non-conforming when they have no choice in the matter) -->
  <!-- XXX mention that this spec doesn't require native support or
  plugin support, either is fine -->

  <h4 id=audio><span class=secno>3.14.8. </span>The <dfn
   id=audio1><code>audio</code></dfn> element</h4>

  <p><a href="#semi-transparent">Semi-transparent</a> <a href="#strictly"
   title="Strictly inline-level content">strictly inline-level</a> <a
   href="#embedded0">embedded content</a>.

  <dl class=element>
   <dt>Contexts in which this element may be used:

   <dd>As the only <a href="#embedded0">embedded content</a> child of a
    <code><a href="#figure">figure</a></code> element.

   <dd>Where <a href="#strictly">strictly inline-level content</a> is
    allowed.

   <dt>Content model:

   <dd>If the element has a <code title=attr-media-src><a
    href="#src5">src</a></code> attribute: <a
    href="#transparent0">transparent</a>.

   <dd>If the element does not have a <code title=attr-media-src><a
    href="#src5">src</a></code> attribute: one or more <code><a
    href="#source">source</a></code> elements, then, <a
    href="#transparent0">transparent</a>.

   <dt>Element-specific attributes:

   <dd><code title=attr-media-src><a href="#src5">src</a></code>

   <dd><code title=attr-media-autoplay><a
    href="#autoplay">autoplay</a></code>

   <dd><code title=attr-media-start><a href="#start2">start</a></code>

   <dd><code title=attr-media-loopstart><a
    href="#loopstart">loopstart</a></code>

   <dd><code title=attr-media-loopend><a href="#loopend">loopend</a></code>

   <dd><code title=attr-media-end><a href="#end">end</a></code>

   <dd><code title=attr-media-loopcount><a
    href="#loopcount">loopcount</a></code>

   <dd><code title=attr-media-controls><a
    href="#controls">controls</a></code>

   <dt>DOM interface:

   <dd>
    <pre
     class=idl>interface <dfn id=htmlaudioelement>HTMLAudioElement</dfn> : <a href="#htmlmediaelement">HTMLMediaElement</a> {
  // no members
};</pre>
  </dl>

  <p>An <code><a href="#audio1">audio</a></code> element represents a sound
   or audio stream.

  <p>Content may be provided inside the <code><a
   href="#audio1">audio</a></code> element so that older Web browsers, which
   do not support <code><a href="#audio1">audio</a></code>, can display text
   to the user informing them of how to access the audio contents. User
   agents should not show this fallback content to the user.

  <p>The <code><a href="#audio1">audio</a></code> element is a <a
   href="#media5">media element</a> whose <a href="#media7">media data</a> is
   ostensibly audio data.

  <p>The <code title=attr-media-src><a href="#src5">src</a></code>, <code
   title=attr-media-autoplay><a href="#autoplay">autoplay</a></code>, <code
   title=attr-media-start><a href="#start2">start</a></code>, <code
   title=attr-media-loopstart><a href="#loopstart">loopstart</a></code>,
   <code title=attr-media-loopend><a href="#loopend">loopend</a></code>,
   <code title=attr-media-end><a href="#end">end</a></code>, <code
   title=attr-media-loopcount><a href="#loopcount">loopcount</a></code>, and
   <code title=attr-media-controls><a href="#controls">controls</a></code>
   attributes are <a href="#media6" title="media element attributes">the
   attributes common to all media elements</a>.

  <p>When an <code><a href="#audio1">audio</a></code> element is <a
   href="#actively">actively playing</a>, it must have its audio data played
   synchronised with the <a href="#current">current playback position</a>, at
   the specified <a href="#volume" title=dom-media-volume>volume</a> with the
   specified <a href="#muted" title=dom-media-muted>mute state</a>.

  <p>When an <code><a href="#audio1">audio</a></code> element is not <a
   href="#actively">actively playing</a>, audio must not play for the
   element.

  <h5 id=audio0><span class=secno>3.14.8.1. </span>Audio codecs for <code><a
   href="#audio1">audio</a></code> elements</h5>

  <p>User agents may support any audio codecs and container formats.

  <p>User agents must support the WAVE container format with audio encoded
   using the PCM format. <!-- XXX references? #refs --></p>
  <!-- XXX mention that this spec doesn't require native support or
  plugin support, either is fine -->

  <h4 id=media><span class=secno>3.14.9. </span>Media elements</h4>

  <p><dfn id=media5 title="media element">Media elements</dfn> implement the
   following interface:

  <pre
   class=idl>interface <dfn id=htmlmediaelement>HTMLMediaElement</dfn> : <a href="#htmlelement">HTMLElement</a> {

  // error state
  readonly attribute <a href="#mediaerror">MediaError</a> <a href="#error0" title=dom-media-error>error</a>;

  // network state
           attribute DOMString <a href="#src6" title=dom-media-src>src</a>;
  readonly attribute DOMString <a href="#currentsrc" title=dom-media-currentSrc>currentSrc</a>;
  const unsigned short <a href="#empty" title=dom-media-EMPTY>EMPTY</a> = 0;
  const unsigned short <a href="#loading0" title=dom-media-LOADING>LOADING</a> = 1;
  const unsigned short <a href="#loadedmetadata" title=dom-media-LOADED_METADATA>LOADED_METADATA</a> = 2;
  const unsigned short <a href="#loadedfirstframe" title=dom-media-LOADED_FIRST_FRAME>LOADED_FIRST_FRAME</a> = 3;
  const unsigned short <a href="#loaded" title=dom-media-LOADED>LOADED</a> = 4;
  readonly attribute unsigned short <a href="#networkstate" title=dom-media-networkState>networkState</a>;
  readonly attribute float <a href="#bufferingrate" title=dom-media-bufferingRate>bufferingRate</a>;
  readonly attribute <a href="#timeranges">TimeRanges</a> <a href="#buffered" title=dom-media-buffered>buffered</a>;
  void <a href="#load" title=dom-media-load>load</a>();

  // ready state
  const unsigned short <a href="#dataunavailable" title=dom-media-DATA_UNAVAILABLE>DATA_UNAVAILABLE</a> = 0;
  const unsigned short <a href="#canshowcurrentframe" title=dom-media-CAN_SHOW_CURRENT_FRAME>CAN_SHOW_CURRENT_FRAME</a> = 1;
  const unsigned short <a href="#canplay" title=dom-media-CAN_PLAY>CAN_PLAY</a> = 2;
  const unsigned short <a href="#canplaythrough" title=dom-media-CAN_PLAY_THROUGH>CAN_PLAY_THROUGH</a> = 3;
  readonly attribute unsigned short <a href="#readystate" title=dom-media-readyState>readyState</a>;
  readonly attribute boolean <a href="#seeking0" title=dom-media-seeking>seeking</a>;

  // playback state
           attribute float <a href="#currenttime" title=dom-media-currentTime>currentTime</a>;
  readonly attribute float <a href="#duration" title=dom-media-duration>duration</a>;
  readonly attribute unsigned short <a href="#paused" title=dom-media-paused>paused</a>;
           attribute float <a href="#defaultplaybackrate" title=dom-media-defaultPlaybackRate>defaultPlaybackRate</a>;
           attribute float <a href="#playbackrate" title=dom-media-playbackRate>playbackRate</a>;
  readonly attribute <a href="#timeranges">TimeRanges</a> <a href="#played" title=dom-media-played>played</a>;
  readonly attribute <a href="#timeranges">TimeRanges</a> <a href="#seekable" title=dom-media-seekable>seekable</a>;
  readonly attribute boolean <a href="#ended0" title=dom-media-ended>ended</a>;
           attribute boolean <a href="#autoplay0" title=dom-media-autoplay>autoplay</a>;
  void <a href="#play" title=dom-media-play>play</a>();
  void <a href="#pause0" title=dom-media-pause>pause</a>();

  // looping
           attribute float <a href="#start3" title=dom-media-start>start</a>;
           attribute float <a href="#end0" title=dom-media-end>end</a>;
           attribute float <a href="#loopstart0" title=dom-media-loopStart>loopStart</a>;
           attribute float <a href="#loopend0" title=dom-media-loopEnd>loopEnd</a>;
           attribute unsigned long <a href="#loopcount0" title=dom-media-loopCount>loopCount</a>;
           attribute unsigned long <a href="#currentloop" title=dom-media-currentLoop>currentLoop</a>;

  // cue points
  void <a href="#addcuepoint" title=dom-media-addCuePoint>addCuePoint</a>(in float time, in <a href="#voidcallback">VoidCallback</a> callback, in bool pause);
  void <a href="#removecuepoint" title=dom-media-removeCuePoint>removeCuePoint</a>(in float time, in <a href="#voidcallback">VoidCallback</a> callback);

  // controls
           attribute boolean <a href="#controls0" title=dom-media-controls>controls</a>;
           attribute float <a href="#volume" title=dom-media-volume>volume</a>;
           attribute boolean <a href="#muted" title=dom-media-muted>muted</a>;
};</pre>

  <p>The <dfn id=media6>media element attributes</dfn>, <code
   title=attr-media-src><a href="#src5">src</a></code>, <code
   title=attr-media-autoplay><a href="#autoplay">autoplay</a></code>, <code
   title=attr-media-start><a href="#start2">start</a></code>, <code
   title=attr-media-loopstart><a href="#loopstart">loopstart</a></code>,
   <code title=attr-media-loopend><a href="#loopend">loopend</a></code>,
   <code title=attr-media-end><a href="#end">end</a></code>, <code
   title=attr-media-loopcount><a href="#loopcount">loopcount</a></code>, and
   <code title=attr-media-controls><a href="#controls">controls</a></code>,
   apply to all <a href="#media5" title="media element">media elements</a>.
   They are defined in this section.</p>
  <!-- XXX v3 features:
    * frame forward / backwards / step(n) while paused
    * hasAudio, hasVideo, hasCaptions, etc
    * per-frame control: get current frame; set current frame
    * queue of content
      - pause current stream and insert content at front of queue to play immediately
      - pre-download another stream
      - add stream(s) to play at end of current stream
      - pause playback upon reaching a certain time
      - playlists, with the ability to get metadata out of them (e.g. xspf)
    * control over closed captions: enable, disable, select language
    * get byte ranges as well as time ranges for buffered data
    * in-band metadata and cue points to allow:
      - Chapter markers that synchronize to playback (without having to poll
        the playhead position)
      - Annotations on video content (i.e., pop-up video)
      - General custom metadata store (ratings, etc.)
    * notification of chapter labels changing on the fly:
      - onchapterlabelupdate, which has a time and a label
    * general meta data, implemented as getters (don't expose the whole thing)
      - getMetadata(key: string, language: string) => HTMLImageElement or string
      - onmetadatachanged (no context info)
  -->

  <p><a href="#media5" title="media element">Media elements</a> are used to
   present audio data, or video and audio data, to the user. This is referred
   to as <dfn id=media7>media data</dfn> in this section, since this section
   applies equally to <a href="#media5" title="media element">media
   elements</a> for audio or for video. The term <dfn id=media8>media
   resource</dfn> is used to refer to the complete set of media data, e.g.
   the complete video file, or complete audio file.

  <h5 id=error><span class=secno>3.14.9.1. </span>Error codes</h5>

  <p>All <a href="#media5" title="media element">media elements</a> have an
   associated error status, which records the last error the element
   encountered since the <code title=dom-media-load><a
   href="#load">load()</a></code> method was last invoked. The <dfn id=error0
   title=dom-media-error><code>error</code></dfn> attribute, on getting, must
   return the <code><a href="#mediaerror">MediaError</a></code> object
   created for this last error, or null if there has not been an error.

  <pre class=idl>interface <dfn id=mediaerror>MediaError</dfn> {
  const unsigned short <a href="#mediaerraborted" title=dom-MediaError-MEDIA_ERR_ABORTED>MEDIA_ERR_ABORTED</a> = 1;
  const unsigned short <a href="#mediaerrnetwork" title=dom-MediaError-MEDIA_ERR_NETWORK>MEDIA_ERR_NETWORK</a> = 2;
  const unsigned short <a href="#mediaerrdecode" title=dom-MediaError-MEDIA_ERR_DECODE>MEDIA_ERR_DECODE</a> = 3;
  readonly attribute unsigned short <a href="#code0" title=dom-MediaError-code>code</a>;
};</pre>

  <p>The <dfn id=code0 title=dom-MediaError-code><code>code</code></dfn>
   attribute of a <code><a href="#mediaerror">MediaError</a></code> object
   must return the code for the error, which must be one of the following:

  <dl>
   <dt><dfn id=mediaerraborted
    title=dom-MediaError-MEDIA_ERR_ABORTED><code>MEDIA_ERR_ABORTED</code></dfn>
    (numeric value 1)

   <dd>The download of the <a href="#media8">media resource</a> was aborted
    by the user agent at the user's request.

   <dt><dfn id=mediaerrnetwork
    title=dom-MediaError-MEDIA_ERR_NETWORK><code>MEDIA_ERR_NETWORK</code></dfn>
    (numeric value 2)

   <dd>A network error of some description caused the user agent to stop
    downloading the <a href="#media8">media resource</a>.

   <dt><dfn id=mediaerrdecode
    title=dom-MediaError-MEDIA_ERR_DECODE><code>MEDIA_ERR_DECODE</code></dfn>
    (numeric value 3)

   <dd>An error of some description occurred while decoding the <a
    href="#media8">media resource</a>.
  </dl>

  <h5 id=location><span class=secno>3.14.9.2. </span>Location of the media
   resource</h5>

  <p>The <dfn id=src5 title=attr-media-src><code>src</code></dfn> content
   attribute on <a href="#media5" title="media element">media elements</a>
   gives the address of the video to show. The attribute, if present, must
   contain a URI (or IRI).

  <p class=note>If a <code title=attr-media-src><a
   href="#src5">src</a></code> attribute is specified, the resource it
   specifies is the <a href="#media8">media resource</a> that will be used.
   Otherwise, the resource specified by the first suitable <code><a
   href="#source">source</a></code> element child of the <a
   href="#media5">media element</a> is the one used.

  <p>The <dfn id=src6 title=dom-media-src><code>src</code></dfn> DOM
   attribute on <a href="#media5" title="media element">media elements</a>
   must <a href="#reflect">reflect</a> the content attribute of the same
   name.

  <p>To <dfn id=pick-a>pick a media resource</dfn> for a <a
   href="#media5">media element</a>, a user agent must follow the following
   steps:

  <ol>
   <li>
    <p>If the <a href="#media5">media element</a> has a <code
     title=attr-media-src><a href="#src5">src</a></code>, then the address
     given in that attribute is the address of the <a href="#media8">media
     resource</a>; jump to the last step.

   <li>
    <p>Otherwise, let <var title="">candidate</var> be the first <code><a
     href="#source">source</a></code> element child in the <a
     href="#media5">media element</a>, or null if there is no such child.

   <li>
    <p>If either:</p>

    <ul>
     <li><var title="">candidate</var> is null, or

     <li>the <var title="">candidate</var> element has no <code
      title=attr-source-src><a href="#src7">src</a></code> attribute, or

     <li>the <var title="">candidate</var> element has a <code
      title=attr-source-type><a href="#type8">type</a></code> attribute and
      that attribute's value, when parsed as a MIME type, does not represent
      a type that the user agent can render (including any codecs described
      by the <code title="">codec</code> parameter), or <a
      href="#refsRFC2046">[RFC2046]</a> <a href="#refsRFC4281">[RFC4281]</a>

     <li>the <var title="">candidate</var> element has a <code
      title=attr-source-media><a href="#media9">media</a></code> attribute
      and that attribute's value, when processed according to the rules for
      media queries, does not match the current environment, <a
      href="#refsMQ">[MQ]</a>
    </ul>

    <p>...then the <var title="">candidate</var> is not suitable; go to the
     next step.</p>

    <p>Otherwise, the address given in that <var title="">candidate</var>
     element's <code title=attr-source-src><a href="#src7">src</a></code>
     attribute is the address of the <a href="#media8">media resource</a>;
     jump to the last step.</p>

   <li>
    <p>Let <var title="">candidate</var> be the next <code><a
     href="#source">source</a></code> element child in the <a
     href="#media5">media element</a>, or null if there are no more such
     children.

   <li>
    <p>If <var title="">candidate</var> is not null, return to step 3.

   <li>
    <p>There is no <a href="#media8">media resource</a>. Abort these steps.

   <li>
    <p>Let the address of the <dfn id=chosen>chosen media resource</dfn> be
     the one that was found before jumping to this step.
  </ol>

  <p>The <dfn id=currentsrc
   title=dom-media-currentSrc><code>currentSrc</code></dfn> DOM attribute
   must return the empty string if the <a href="#media5">media element</a>'s
   <code title=dom-media-networkState><a
   href="#networkstate">networkState</a></code> has the value <a
   href="#empty" title=dom-media-EMPTY>EMPTY</a>, and the absolute URL of the
   <a href="#chosen">chosen media resource</a> otherwise.

  <h5 id=network0><span class=secno>3.14.9.3. </span>Network states</h5>

  <p>As <a href="#media5" title="media element">media elements</a> interact
   with the network, they go through several states. The <dfn id=networkstate
   title=dom-media-networkState><code>networkState</code></dfn> attribute, on
   getting, must return the current network state of the element, which must
   be one of the following values:

  <dl>
   <dt><dfn id=empty title=dom-media-EMPTY><code>EMPTY</code></dfn> (numeric
    value 0)

   <dd>The element has not yet been initialised. All attributes are in their
    initial states.

   <dt><dfn id=loading0 title=dom-media-LOADING><code>LOADING</code></dfn>
    (numeric value 1)

   <dd>The element has <a href="#pick-a" title="pick a media resource">picked
    a media resource</a> (the <a href="#chosen">chosen media resource</a> is
    available from the <code title=dom-media-currentSrc><a
    href="#currentsrc">currentSrc</a></code> attribute), but none of the
    metadata has yet been obtained and therefore all the other attributes are
    still in their initial states.

   <dt><dfn id=loadedmetadata
    title=dom-media-LOADED_METADATA><code>LOADED_METADATA</code></dfn>
    (numeric value 2)

   <dd>Enough of the resource has been obtained that the metadata attributes
    are initialized (e.g. the length is known). The API will no longer raise
    exceptions when used.

   <dt><dfn id=loadedfirstframe
    title=dom-media-LOADED_FIRST_FRAME><code>LOADED_FIRST_FRAME</code></dfn>
    (numeric value 3)

   <dd>Actual <a href="#media7">media data</a> has been obtained. In the case
    of video, this specifically means that a frame of video is available and
    can be shown.

   <dt><dfn id=loaded title=dom-media-LOADED><code>LOADED</code></dfn>
    (numeric value 4)

   <dd>The entire <a href="#media8">media resource</a> has been obtained and
    is available to the user agent locally. Network connectivity could be
    lost without affecting the media playback.
  </dl>

  <p>The algorithm for the <code title=dom-media-load><a
   href="#load">load()</a></code> method defined below describes exactly when
   the <code title=dom-media-networkState><a
   href="#networkstate">networkState</a></code> attribute changes value.

  <h5 id=loading><span class=secno>3.14.9.4. </span>Loading the media
   resource</h5>

  <p>All <a href="#media5" title="media element">media elements</a> have a
   <dfn id=begun>begun flag</dfn>, which must begin in the false state, a
   <dfn id=loaded-first-frame>loaded-first-frame flag</dfn>, which must begin
   in the false state, and an <dfn id=autoplaying>autoplaying flag</dfn>,
   which must begin in the true state.

  <p>When the <dfn id=load title=dom-media-load><code>load()</code></dfn>
   method on a <a href="#media5">media element</a> is invoked, the user agent
   must run the following steps. Note that this algorithm might get aborted,
   e.g. if the <code title=dom-media-load><a href="#load">load()</a></code>
   method itself is invoked again.

  <ol>
   <li>
    <p>Any already-running instance of this algorithm for this element must
     be aborted. If those method calls have not yet returned, they must
     finish the step they are on, and then immediately return.

   <li>
    <p>If the element's <a href="#begun">begun flag</a> is true, then the <a
     href="#begun">begun flag</a> must be set to false, the <code
     title=dom-media-error><a href="#error0">error</a></code> attribute must
     be set to a new <code><a href="#mediaerror">MediaError</a></code> object
     whose <code title=dom-MediaError-code><a href="#code0">code</a></code>
     attribute is set to <code title=dom-MediaError-MEDIA_ERR_ABORTED><a
     href="#mediaerraborted">MEDIA_ERR_ABORTED</a></code>, and the user agent
     must synchronously <a href="#firing6">fire a progress event</a> called
     <code title=event-abort><a href="#abort">abort</a></code> at the <a
     href="#media5">media element</a>.

   <li>
    <p>The <code title=dom-media-error><a href="#error0">error</a></code>
     attribute must be set to null, and the <a
     href="#loaded-first-frame">loaded-first-frame flag</a> and
     <span>loaded-enough-to-play-through flag</span> must be both set to
     false.

   <li>
    <p>The <code title=dom-media-playbackRate><a
     href="#playbackrate">playbackRate</a></code> attribute must be set to
     the value of the <code title=dom-media-defaultPlaybackRate><a
     href="#defaultplaybackrate">defaultPlaybackRate</a></code> attribute.

   <li>
    <p>If the <a href="#media5">media element</a>'s <code
     title=dom-media-networkState><a
     href="#networkstate">networkState</a></code> is not set to <a
     href="#empty" title=dom-media-EMPTY>EMPTY</a>, then the following
     substeps must be followed:

    <ol><!--<li>Let <var title="">events</var> be a list of event names,
     initially empty.</li>-->

     <li>The <code title=dom-media-networkState><a
      href="#networkstate">networkState</a></code> attribute must be set to
      <a href="#empty"
      title=dom-media-EMPTY>EMPTY</a><!--, and the user agent must
     add <code title="event-emptied">emptied</code> to the <var
     title="">events</var> list-->.

     <li>If <code title=dom-media-readyState><a
      href="#readystate">readyState</a></code> is not set to <code
      title=dom-media-DATA_UNAVAILABLE><a
      href="#dataunavailable">DATA_UNAVAILABLE</a></code>, it must be set to
      that state<!-- and the user agent must add <code
     title="event-dataunavailable">dataunavailable</code> to the
     <var title="">events</var> list-->.

     <li>If the <code title=dom-media-paused><a
      href="#paused">paused</a></code> attribute is false, it must be set to
      true<!--, and the user agent must add
     <code title="event-pause">pause</code> to the <var
     title="">events</var> list-->.

     <li>If <code title=dom-media-seeking><a
      href="#seeking0">seeking</a></code> is true, it must be set to false.

     <li>The <a href="#current">current playback position</a> must be set to
      0.

     <li>The <code title=dom-media-currentLoop><a
      href="#currentloop">currentLoop</a></code> DOM attribute must be set to
      0.</li>
     <!--<li>The user agent must synchronously <span>fire a simple
     event</span> at the <span>media element</span> for each event
     name in <var title="">events</var>, in the same order that they
     were added to that list.</li>-->

     <li>The user agent must synchronously <a href="#firing2">fire a simple
      event</a> called <code title=event-emptied><a
      href="#emptied">emptied</a></code> at the <a href="#media5">media
      element</a>.
    </ol>

   <li>
    <p>The user agent must <a href="#pick-a">pick a media resource</a> for
     the <a href="#media5">media element</a>. If that fails, the method must
     raise an <code>INVALID_STATE_ERR</code> exception, and abort these
     steps.

   <li>
    <p>The <code title=dom-media-networkState><a
     href="#networkstate">networkState</a></code> attribute must be set to <a
     href="#loading0" title=dom-media-LOADING>LOADING</a>.

   <li>
    <p class=note>The <code title=dom-media-currentSrc><a
     href="#currentsrc">currentSrc</a></code> attribute starts returning the
     new value.

   <li>
    <p>The user agent must then set the <a href="#begun">begun flag</a> to
     true and <a href="#firing6">fire a progress event</a> called
     <code>begin</code> at the <a href="#media5">media element</a>.

   <li>
    <p>The method must return, but these steps must continue.

   <li>
    <p class=note>Playback of any previously playing <a href="#media8">media
     resource</a> for this element stops.

   <li>
    <p>If a download is in progress for the <a href="#media5">media
     element</a>, the user agent should stop the download.

   <li>
    <p>The user agent must then begin to download the <a
     href="#chosen">chosen media resource</a>. The rate of the download may
     be throttled, however, in response to user preferences (including
     throttling it to zero until the user indicates that the download can
     start), or to balance the download with other connections sharing the
     same bandwidth.

   <li>
    <p>While the download is progressing, the user agent must <a
     href="#firing6">fire a progress event</a> called <code
     title=event-progress><a href="#progress0">progress</a></code> at the
     element every 350ms (&#xB1;200ms) or for every byte received, whichever
     is <em>least</em> frequent.</p>

    <p>If at any point the user agent has received no data for more than
     about three seconds, the user agent must <a href="#firing6">fire a
     progress event</a> called <code title=event-stalled><a
     href="#stalled">stalled</a></code> at the element.</p>

    <p>User agents may allow users to selectively block or slow <a
     href="#media7">media data</a> downloads. When a <a href="#media5">media
     element</a>'s download has been blocked, the user agent must act as if
     it was stalled (as opposed to acting as if the connection was closed).</p>

    <p>The user agent may use whatever means necessary to download the
     resource (within the constraints put forward by this and other
     specifications); for example, reconnecting to the server in the face of
     network errors, using HTTP partial range requests, or switching to a
     streaming protocol. The user agent must only consider a resource
     erroneous if it has given up trying to download it.</p>

    <dl class=switch>
     <dt>If the <a href="#media7">media data</a> cannot be downloaded at all,
      due to network errors, causing the user agent to give up trying to
      download the resource

     <dd>
      <p>DNS errors and HTTP 4xx and 5xx errors (and equivalents in other
       protocols) must cause the user agent to follow the following steps.
       User agents may also follow these steps in response to other network
       errors of similar severity.</p>

      <ol>
       <li>The user agent should cancel the download.

       <li>The <code title=dom-media-error><a href="#error0">error</a></code>
        attribute must be set to a new <code><a
        href="#mediaerror">MediaError</a></code> object whose <code
        title=dom-MediaError-code><a href="#code0">code</a></code> attribute
        is set to <code title=dom-MediaError-MEDIA_ERR_NETWORK><a
        href="#mediaerrnetwork">MEDIA_ERR_NETWORK</a></code>.

       <li>The <a href="#begun">begun flag</a> must be set to false and the
        user agent must <a href="#firing6">fire a progress event</a> called
        <code title=event-error><a href="#error1">error</a></code> at the <a
        href="#media5">media element</a>.

       <li>The element's <code title=dom-media-networkState><a
        href="#networkstate">networkState</a></code> attribute must be
        switched to the <a href="#empty" title=dom-media-EMPTY>EMPTY</a>
        value and the user agent must <a href="#firing2">fire a simple
        event</a> called <code title=event-emptied><a
        href="#emptied">emptied</a></code> at the element.

       <li>These steps must be aborted.
      </ol>

     <dt id=fatal-decode-error>If the <a href="#media7">media data</a> can be
      downloaded but is in an unsupported format, or can otherwise not be
      properly rendered at all

     <dd>
      <p>The server returning a file of the wrong kind (e.g. one that that
       turns out to not be pure audio when the <a href="#media5">media
       element</a> is a <code><a href="#audio1">audio</a></code> element), or
       the file using unsupported codecs for all the data, must cause the
       user agent to follow the following steps. User agents may also follow
       these steps in response to other codec-related fatal errors, such as
       the file requiring more resources to process than the user agent can
       provide in real time.</p>

      <ol>
       <li>The user agent should cancel the download.

       <li>The <code title=dom-media-error><a href="#error0">error</a></code>
        attribute must be set to a new <code><a
        href="#mediaerror">MediaError</a></code> object whose <code
        title=dom-MediaError-code><a href="#code0">code</a></code> attribute
        is set to <code title=dom-MediaError-MEDIA_ERR_DECODE><a
        href="#mediaerrdecode">MEDIA_ERR_DECODE</a></code>.

       <li>The <a href="#begun">begun flag</a> must be set to false and the
        user agent must <a href="#firing6">fire a progress event</a> called
        <code title=event-error><a href="#error1">error</a></code> at the <a
        href="#media5">media element</a>.

       <li>The element's <code title=dom-media-networkState><a
        href="#networkstate">networkState</a></code> attribute must be
        switched to the <a href="#empty" title=dom-media-EMPTY>EMPTY</a>
        value and the user agent must <a href="#firing2">fire a simple
        event</a> called <code title=event-emptied><a
        href="#emptied">emptied</a></code> at the element.

       <li>These steps must be aborted.
      </ol>

     <dt>If the <a href="#media7">media data</a> download is aborted by the
      user

     <dd>
      <p>The download is aborted by the user, e.g. because the user navigated
       the browsing context to another page, the user agent must follow the
       following steps. These steps are not followed if the <code
       title=dom-media-load><a href="#load">load()</a></code> method itself
       is reinvoked, as the steps above handle that particular kind of abort.</p>

      <ol>
       <li>The user agent should cancel the download.

       <li>The <code title=dom-media-error><a href="#error0">error</a></code>
        attribute must be set to a new <code><a
        href="#mediaerror">MediaError</a></code> object whose <code
        title=dom-MediaError-code><a href="#code0">code</a></code> attribute
        is set to <code
        title=dom-MediaError-MEDIA_ERR_ABORT>MEDIA_ERR_ABORT</code>.

       <li>The <a href="#begun">begun flag</a> must be set to false and the
        user agent must <a href="#firing6">fire a progress event</a> called
        <code title=event-abort><a href="#abort">abort</a></code> at the <a
        href="#media5">media element</a>.

       <li>If the <a href="#media5">media element</a>'s <code
        title=dom-media-networkState><a
        href="#networkstate">networkState</a></code> attribute has the value
        <code title=dom-media-LOADING><a href="#loading0">LOADING</a></code>,
        the element's <code title=dom-media-networkState><a
        href="#networkstate">networkState</a></code> attribute must be
        switched to the <a href="#empty" title=dom-media-EMPTY>EMPTY</a>
        value and the user agent must <a href="#firing2">fire a simple
        event</a> called <code title=event-emptied><a
        href="#emptied">emptied</a></code> at the element.

       <li>These steps must be aborted.
      </ol>

     <dt id=non-fatal-media-error>If the <a href="#media7">media data</a> can
      be downloaded but has non-fatal errors or uses, in part, codecs that
      are unsupported, preventing the user agent from rendering the content
      completely correctly but not preventing playback altogether

     <dd>
      <p>The server returning data that is partially usable but cannot be
       optimally rendered must cause the user agent to follow the following
       steps.</p>

      <ol>
       <li class=big-issue>Should we fire a 'warning' event? Set the 'error'
        flag to 'MEDIA_ERR_SUBOPTIMAL' or something?
      </ol>

     <dt>Once enough of the <a href="#media7">media data</a> has been
      downloaded to determine the duration of the <a href="#media8">media
      resource</a>, its dimensions, and other metadata

     <dd>
      <p>The user agent must follow these substeps:</p>

      <ol>
       <li>
        <p>The <a href="#current">current playback position</a> must be set
         to the <var><a href="#effective">effective start</a></var>.

       <li>
        <p>The <code title=dom-media-networkState><a
         href="#networkstate">networkState</a></code> attribute must be set
         to <code title=dom-media-LOADED_METADATA><a
         href="#loadedmetadata">LOADED_METADATA</a></code>.

       <li>
        <p class=note>A number of attributes, including <code
         title=dom-media-duration><a href="#duration">duration</a></code>,
         <code title=dom-media-buffered><a
         href="#buffered">buffered</a></code>, and <code
         title=dom-media-played><a href="#played">played</a></code>, become
         available.

       <li>
        <p class=note>The user agent will <a href="#firing2">fire a simple
         event</a> called <code title=event-durationchange><a
         href="#durationchange">durationchange</a></code> at the element at
         this point.

       <li>
        <p>The user agent must <a href="#firing2">fire a simple event</a>
         called <code title=event-loadedmetadata><a
         href="#loadedmetadata0">loadedmetadata</a></code> at the element.
      </ol>

     <dt id=handling-first-frame-available>Once enough of the <a
      href="#media7">media data</a> has been downloaded to enable the user
      agent to display the first frame of the <a href="#media8">media
      resource</a>

     <dd>
      <p>The user agent must follow these substeps:</p>

      <ol>
       <li>
        <p>The <code title=dom-media-networkState><a
         href="#networkstate">networkState</a></code> attribute must be set
         to <code title=dom-media-LOADED_FIRST_FRAME><a
         href="#loadedfirstframe">LOADED_FIRST_FRAME</a></code>.

       <li>
        <p>The <code title=dom-media-readyState><a
         href="#readystate">readyState</a></code> attribute must change to
         <code title=dom-media-CAN_SHOW_CURRENT_FRAME><a
         href="#canshowcurrentframe">CAN_SHOW_CURRENT_FRAME</a></code>.

       <li>
        <p>The <a href="#loaded-first-frame">loaded-first-frame flag</a> must
         be set to true.

       <li>
        <p>The user agent must <a href="#firing2">fire a simple event</a>
         called <code title=event-loadedfirstfame>loadedfirstframe</code> at
         the element.

       <li>
        <p>The user agent must <a href="#firing2">fire a simple event</a>
         called <code title=event-canshowcurrentframe><a
         href="#canshowcurrentframe0">canshowcurrentframe</a></code> at the
         element.
      </ol>
    </dl>

    <p>When the user agent has completed the download of the entire <a
     href="#media8">media resource</a>, it must move on to the next step.</p>

   <li>
    <p>If the download completes without errors, the <a href="#begun">begun
     flag</a> must be set to false and the user agent must <a
     href="#firing6">fire a progress event</a> called <code
     title=event-load><a href="#load0">load</a></code> at the element.
  </ol>

  <p>If a <a href="#media5">media element</a> whose <code
   title=dom-media-networkState><a
   href="#networkstate">networkState</a></code> has the value <code
   title=dom-media-EMPTY><a href="#empty">EMPTY</a></code> is inserted into a
   document, user agents must implicitly invoke the <code
   title=dom-media-load><a href="#load">load()</a></code> method on the <a
   href="#media5">media element</a> as soon as all other scripts have
   finished executing<!-- XXX phrase that better? -->. Any exceptions raised
   must be ignored.

  <p>The <dfn id=bufferingrate
   title=dom-media-bufferingRate><code>bufferingRate</code></dfn> attribute
   must return the average number of bits received per second for the current
   download over the past few seconds. If there is no download in progress,
   the attribute must return 0.

  <p>The <dfn id=buffered
   title=dom-media-buffered><code>buffered</code></dfn> attribute must return
   a static <a href="#normalised">normalised <code>TimeRanges</code>
   object</a> that represents the ranges of the <a href="#media8">media
   resource</a>, if any, that the user agent has downloaded, at the time the
   attribute is evaluated.

  <p class=note>Typically this will be a single range anchored at the zero
   point, but if, e.g. the user agent uses HTTP range requests in response to
   seeking, then there could be multiple ranges.

  <h5 id=offsets><span class=secno>3.14.9.5. </span>Offsets into the media
   resource</h5>

  <p>The <dfn id=duration
   title=dom-media-duration><code>duration</code></dfn> attribute must return
   the length of the <a href="#media8">media resource</a>, in seconds. If no
   <a href="#media7">media data</a> is available, then the attributes must
   return 0. If <a href="#media7">media data</a> is available but the length
   is not known, the attribute must return the Not-a-Number (NaN) value. If
   the <a href="#media8">media resource</a> is known to be unbounded (e.g. a
   streaming radio), then the attribute must return the positive Infinity
   value.

  <p>When the length of the <a href="#media8">media resource</a> changes
   (e.g. from being unknown to known, or from indeterminate to known, or from
   a previously established length to a new length) the user agent must, once
   any running scripts have finished, <a href="#firing2">fire a simple
   event</a> called <code title=event-durationchange><a
   href="#durationchange">durationchange</a></code> at the <a
   href="#media5">media element</a>.

  <p><a href="#media5" title="media element">Media elements</a> have a <dfn
   id=current>current playback position</dfn>, which must initially be zero.
   The current position is a time.

  <p>The <dfn id=currenttime
   title=dom-media-currentTime><code>currentTime</code></dfn> attribute must,
   on getting, return the <a href="#current">current playback position</a>,
   expressed in seconds. On setting, the user agent must <a href="#seek"
   title=dom-media-seek>seek</a> to the new value.

  <p>The <dfn id=start2 title=attr-media-start><code>start</code></dfn>
   content attribute gives the offset into the <a href="#media8">media
   resource</a> at which playback is to begin. The default value is 0.

  <p>The <dfn id=effective><var>effective start</var></dfn> is the smaller of
   <code title=dom-media-start><a href="#start3">start</a></code> and the end
   of the <a href="#media8">media resource</a>.

  <p>

  <p>The <dfn id=loopstart
   title=attr-media-loopstart><code>loopstart</code></dfn> content attribute
   gives the offset into the <a href="#media8">media resource</a> at which
   playback is to begin when looping a clip. The default value is 0.

  <p>The <dfn id=effective0><var>effective loop start</var></dfn> is the
   smaller of <code title=dom-media-loopStart><a
   href="#loopstart0">loopStart</a></code> and the end of the <a
   href="#media8">media resource</a>.

  <p>

  <p>The <dfn id=loopend title=attr-media-loopend><code>loopend</code></dfn>
   content attribute gives an offset into the <a href="#media8">media
   resource</a> at which playback is to jump back to the <code
   title=attr-media-loopstart><a href="#loopstart">loopstart</a></code>, when
   looping the clip. The default value is infinity.

  <p>The <dfn id=effective1><var>effective loop end</var></dfn> is the
   greater of <code title=dom-media-start><a href="#start3">start</a></code>,
   <code title=dom-media-loopStart><a
   href="#loopstart0">loopStart</a></code>, and <code
   title=dom-media-loopEnd><a href="#loopend0">loopEnd</a></code>, and the
   end of the <a href="#media8">media resource</a>.

  <p>

  <p>The <dfn id=end title=attr-media-end><code>end</code></dfn> content
   attribute gives an offset into the <a href="#media8">media resource</a> at
   which playback is to end. The default value is infinity.

  <p>The <dfn id=effective2><var>effective end</var></dfn> is the greater of
   <code title=dom-media-start><a href="#start3">start</a></code>, <code
   title=dom-media-loopStart><a href="#loopstart0">loopStart</a></code>,
   <code title=dom-media-loopEnd><a href="#loopend0">end</a></code>, and the
   end of the <a href="#media8">media resource</a>.

  <p>

  <p>The <code title=attr-media-start><a href="#start2">start</a></code>,
   <code title=attr-media-loopstart><a
   href="#loopstart">loopstart</a></code>, <code title=attr-media-loopend><a
   href="#loopend">loopend</a></code>, and <code title=attr-media-end><a
   href="#end">end</a></code> attributes must, if specified, contain <span
   title="value time offset">value time offsets</span>. To get the time
   values they represent, user agents must use the <a href="#rules4">rules
   for parsing time offsets</a>.

  <p>The <dfn id=start3 title=dom-media-start><code>start</code></dfn>, <dfn
   id=loopstart0 title=dom-media-loopStart><code>loopStart</code></dfn>, <dfn
   id=loopend0 title=dom-media-loopEnd><code>loopEnd</code></dfn>, and <dfn
   id=end0 title=dom-media-end><code>end</code></dfn> DOM attributes must <a
   href="#reflect">reflect</a> the <code title=attr-media-start><a
   href="#start2">start</a></code>, <code title=attr-media-loopstart><a
   href="#loopstart">loopstart</a></code>, <code title=attr-media-loopend><a
   href="#loopend">loopend</a></code>, and <code title=attr-media-end><a
   href="#end">end</a></code> content attributes on the <a
   href="#media5">media element</a> respectively.

  <p>The <dfn id=loopcount
   title=attr-media-loopcount><code>loopcount</code></dfn> content attribute
   gives the number of times to play the clip. The default value is 1.

  <p>The <dfn id=loopcount0
   title=dom-media-loopCount><code>loopCount</code></dfn> DOM attribute must
   <a href="#reflect">reflect</a> the <code title=attr-media-loopcount><a
   href="#loopcount">loopcount</a></code> content attribute on the <a
   href="#media5">media element</a>. The value must be <a
   href="#limited0">limited to only positive non-zero numbers</a>.

  <p>The <dfn id=currentloop
   title=dom-media-currentLoop><code>currentLoop</code></dfn> attribute must
   initially have the value 0. It gives the index of the current loop. It is
   changed during playback as described below.

  <p>When any of the <code title=dom-media-start><a
   href="#start3">start</a></code>, <code title=dom-media-loopStart><a
   href="#loopstart0">loopStart</a></code>, <code title=dom-media-loopEnd><a
   href="#loopend0">loopEnd</a></code>, <code title=dom-media-end><a
   href="#end0">end</a></code>, and <code title=dom-media-loopCount><a
   href="#loopcount0">loopCount</a></code> DOM attributes change value
   (either through content attribute mutations reflecting into the DOM
   attribute, or direct mutations of the DOM attribute), the user agent must
   apply the following steps:

  <ol>
   <li>
    <p>If the <code title=dom-media-loopCount><a
     href="#loopcount0">loopCount</a></code> DOM attribute's value is less
     than the <code title=dom-media-currentLoop><a
     href="#currentloop">currentLoop</a></code> DOM attribute's value, then
     the <code title=dom-media-currentLoop><a
     href="#currentloop">currentLoop</a></code> DOM attribute's value must be
     set to the value of the <code title=dom-media-loopCount><a
     href="#loopcount0">loopCount</a></code> DOM attribute's value (which
     will make the current loop the last loop).

   <li>
    <p>If the <a href="#media5">media element</a>'s <code
     title=dom-media-networkState><a
     href="#networkstate">networkState</a></code> is in the <code
     title=dom-media-EMPTY><a href="#empty">EMPTY</a></code> state or the
     <code title=dom-media-LOADING><a href="#loading0">LOADING</a></code>
     state, then the user agent must at this point abort these steps.

   <li>
    <p>If the <code title=dom-media-currentLoop><a
     href="#currentloop">currentLoop</a></code> is zero, and the <a
     href="#current">current playback position</a> is before the <var><a
     href="#effective">effective start</a></var>, the user agent must <a
     href="#seek" title=dom-media-seek>seek</a> to the <var><a
     href="#effective">effective start</a></var>.

   <li>
    <p>If the <code title=dom-media-currentLoop><a
     href="#currentloop">currentLoop</a></code> is greater than zero, and the
     <a href="#current">current playback position</a> is before the <var><a
     href="#effective0">effective loop start</a></var>, the user agent must
     <a href="#seek" title=dom-media-seek>seek</a> to the <var><a
     href="#effective0">effective loop start</a></var>.

   <li>
    <p>If the <code title=dom-media-currentLoop><a
     href="#currentloop">currentLoop</a></code> is less than <code
     title=dom-media-loopCount><a href="#loopcount0">loopCount</a></code>,
     and the <a href="#current">current playback position</a> is after the
     <var><a href="#effective1">effective loop end</a></var>, the user agent
     must <a href="#seek" title=dom-media-seek>seek</a> to the <var><a
     href="#effective0">effective loop start</a></var>, and increase <code
     title=dom-media-loopCount><a href="#loopcount0">loopCount</a></code> by
     1.

   <li>
    <p>If the <code title=dom-media-currentLoop><a
     href="#currentloop">currentLoop</a></code> is equal to the <code
     title=dom-media-loopCount><a href="#loopcount0">loopCount</a></code>,
     and the <a href="#current">current playback position</a> is after the
     <var><a href="#effective2">effective end</a></var>, the user agent must
     <a href="#seek" title=dom-media-seek>seek</a> to the <var><a
     href="#effective2">effective end</a></var> and then the looping will
     end.
  </ol>

  <h5 id=the-ready><span class=secno>3.14.9.6. </span>The ready states</h5>

  <p><a href="#media5" title="media element">Media elements</a> have a
   <em>ready state</em>, which describes to what degree they are ready to be
   rendered at the <a href="#current">current playback position</a>. The
   possible values are as follows; the ready state of a media element at any
   particular time is the greatest value describing the state of the element:

  <dl>
   <dt><dfn id=dataunavailable
    title=dom-media-DATA_UNAVAILABLE><code>DATA_UNAVAILABLE</code></dfn>
    (numeric value 0)

   <dd>No data for the <a href="#current">current playback position</a> is
    available. <a href="#media5" title="media element">Media elements</a>
    whose <code title=dom-media-networkState><a
    href="#networkstate">networkState</a></code> attribute is less than <code
    title=dom-media-LOADED_FIRST_FRAME><a
    href="#loadedfirstframe">LOADED_FIRST_FRAME</a></code> are always in the
    <code title=dom-media-DATA_UNAVAILABLE><a
    href="#dataunavailable">DATA_UNAVAILABLE</a></code> state.

   <dt><dfn id=canshowcurrentframe
    title=dom-media-CAN_SHOW_CURRENT_FRAME><code>CAN_SHOW_CURRENT_FRAME</code></dfn>
    (numeric value 1)

   <dd>Data for the immediate <a href="#current">current playback
    position</a> is available, but not enough data is available that the user
    agent could successfully advance the <a href="#current">current playback
    position</a> at all without immediately reverting to the <code
    title=dom-media-DATA_UNAVAILABLE><a
    href="#dataunavailable">DATA_UNAVAILABLE</a></code> state. In video, this
    corresponds to the user agent having data from the current frame, but not
    the next frame. In audio, this corresponds to the user agent only having
    audio up to the <a href="#current">current playback position</a>, but no
    further.

   <dt><dfn id=canplay title=dom-media-CAN_PLAY><code>CAN_PLAY</code></dfn>
    (numeric value 2)

   <dd>Data for the immediate <a href="#current">current playback
    position</a> is available, as well as enough data for the user agent to
    advance the <a href="#current">current playback position</a> at least a
    little without immediately reverting to the <code
    title=dom-media-DATA_UNAVAILABLE><a
    href="#dataunavailable">DATA_UNAVAILABLE</a></code> state. In video, this
    corresponds to the user agent having data for the current frame and the
    next frame. In audio, this corresponds ot the user agent having data
    beyond the <a href="#current">current playback position</a>.

   <dt><dfn id=canplaythrough
    title=dom-media-CAN_PLAY_THROUGH><code>CAN_PLAY_THROUGH</code></dfn>
    (numeric value 3)

   <dd>Data for the immediate <a href="#current">current playback
    position</a> is available, as well as enough data for the user agent to
    advance the <a href="#current">current playback position</a> at least a
    little without immediately reverting to the <code
    title=dom-media-DATA_UNAVAILABLE><a
    href="#dataunavailable">DATA_UNAVAILABLE</a></code> state, and, in
    addition, the user agent estimates that data is being downloaded at a
    rate where the <a href="#current">current playback position</a>, if it
    were to advance at the rate given by the <code
    title=dom-media-defaultPlaybackRate><a
    href="#defaultplaybackrate">defaultPlaybackRate</a></code> attribute,
    would not overtake the available data before playback reaches the <a
    href="#effective2">effective end</a> of the <a href="#media8">media
    resource</a> on the last <a href="#loopcount0"
    title=dom-media-loopCount>loop</a>.
  </dl>

  <p>When the ready state of a <a href="#media5">media element</a> whose
   <code title=dom-media-networkState><a
   href="#networkstate">networkState</a></code> is not <code
   title=dom-media-EMPTY><a href="#empty">EMPTY</a></code> changes, the user
   agent must follow the steps given below:

  <dl class=switch>
   <dt>If the new ready state is <code title=dom-media-DATA_UNAVAILABLE><a
    href="#dataunavailable">DATA_UNAVAILABLE</a></code>

   <dd>
    <p>The user agent must <a href="#firing2">fire a simple event</a> called
     <code title=event-dataunavailable><a
     href="#dataunavailable0">dataunavailable</a></code> at the element.

   <dt>If the new ready state is <code
    title=dom-media-CAN_SHOW_CURRENT_FRAME><a
    href="#canshowcurrentframe">CAN_SHOW_CURRENT_FRAME</a></code>

   <dd>
    <p>If the element's <a href="#loaded-first-frame">loaded-first-frame
     flag</a> is true, the user agent must <a href="#firing2">fire a simple
     event</a> called <code title=event-canshowcurrentframe><a
     href="#canshowcurrentframe0">canshowcurrentframe</a></code> event.</p>

    <p class=note>The first time the <code title=dom-media-networkState><a
     href="#networkstate">networkState</a></code> attribute switches to this
     value, the <a href="#loaded-first-frame">loaded-first-frame flag</a> is
     false, and the event is fired <a
     href="#handling-first-frame-available">by the algorithm described
     above</a> for the <code title=dom-media-load><a
     href="#load">load()</a></code> method, in conjunction with other steps.</p>

   <dt>If the new ready state is <code title=dom-media-CAN_PLAY><a
    href="#canplay">CAN_PLAY</a></code>

   <dd>
    <p>The user agent must <a href="#firing2">fire a simple event</a> called
     <code title=event-canplay><a href="#canplay0">canplay</a></code>.

   <dt>If the new ready state is <code title=dom-media-CAN_PLAY_THROUGH><a
    href="#canplaythrough">CAN_PLAY_THROUGH</a></code>

   <dd>
    <p>The user agent must <a href="#firing2">fire a simple event</a> called
     <code title=event-canplaythrough><a
     href="#canplaythrough0">canplaythrough</a></code> event. If the <a
     href="#autoplaying">autoplaying flag</a> is true, and the <code
     title=dom-media-paused><a href="#paused">paused</a></code> attribute is
     true, and the <a href="#media5">media element</a> has an <code
     title=attr-media-autoplay><a href="#autoplay">autoplay</a></code>
     attribute specified, then the user agent must also set the <code
     title=dom-media-paused><a href="#paused">paused</a></code> attribute to
     false and <a href="#firing2">fire a simple event</a> called <code
     title=event-play><a href="#play0">play</a></code>.
  </dl>

  <p>The <dfn id=readystate
   title=dom-media-readyState><code>readyState</code></dfn> DOM attribute
   must, on getting, return the value described above that describes the
   current ready state of the <a href="#media5">media element</a>.

  <p>The <dfn id=autoplay
   title=attr-media-autoplay><code>autoplay</code></dfn> attribute is a <a
   href="#boolean0">boolean attribute</a>. When present, the algorithm
   described herein will cause the user agent to automatically begin playback
   of the <a href="#media8">media resource</a> as soon as it can do so
   without stopping.

  <p>The <dfn id=autoplay0
   title=dom-media-autoplay><code>autoplay</code></dfn> DOM attribute must <a
   href="#reflect">reflect</a> the content attribute of the same name.

  <h5 id=playing><span class=secno>3.14.9.7. </span>Playing the media
   resource</h5>

  <p>The <dfn id=paused title=dom-media-paused><code>paused</code></dfn>
   attribute represents whether the <a href="#media5">media element</a> is
   paused or not. The attribute must initially be true.

  <p>A <a href="#media5">media element</a> is said to be <dfn
   id=actively>actively playing</dfn> when its <code
   title=dom-media-paused><a href="#paused">paused</a></code> attribute is
   false, the <code title=dom-media-readyState><a
   href="#readystate">readyState</a></code> attribute is either <code
   title=dom-media-CAN_PLAY><a href="#canplay">CAN_PLAY</a></code> or <code
   title=dom-media-CAN_PLAY_THROUGH><a
   href="#canplaythrough">CAN_PLAY_THROUGH</a></code>, the element has not <a
   href="#ended">ended playback</a>, playback has not <a
   href="#stopped">stopped due to errors</a>, and the element has not <a
   href="#paused0">paused for user interaction</a>.

  <p>A <a href="#media5">media element</a> is said to have <dfn
   id=ended>ended playback</dfn> when the element's <code
   title=dom-media-networkState><a
   href="#networkstate">networkState</a></code> attribute is <code
   title=dom-media-LOADED_METADATA><a
   href="#loadedmetadata">LOADED_METADATA</a></code> or greater, the <a
   href="#current">current playback position</a> is equal to the <var><a
   href="#effective2">effective end</a></var> of the <a href="#media8">media
   resource</a>, and the <code title=dom-media-currentLoop><a
   href="#currentloop">currentLoop</a></code> attribute is equal to the <code
   title=dom-media-loopCount><a href="#loopcount0">loopCount</a></code> DOM
   attribute.

  <p>A <a href="#media5">media element</a> is said to have <dfn
   id=stopped>stopped due to errors</dfn> when the element's <code
   title=dom-media-networkState><a
   href="#networkstate">networkState</a></code> attribute is <code
   title=dom-media-LOADED_METADATA><a
   href="#loadedmetadata">LOADED_METADATA</a></code> or greater, and the user
   agent has <a href="#non-fatal-media-error">encounters a non-fatal
   error</a> during the processing of the <a href="#media7">media data</a>,
   and due to that error, is not able to play the content at the <a
   href="#current">current playback position</a>.

  <p>A <a href="#media5">media element</a> is said to have <dfn
   id=paused0>paused for user interaction</dfn> when its <code
   title=dom-media-paused><a href="#paused">paused</a></code> attribute is
   false, the <code title=dom-media-readyState><a
   href="#readystate">readyState</a></code> attribute is either <code
   title=dom-media-CAN_PLAY><a href="#canplay">CAN_PLAY</a></code> or <code
   title=dom-media-CAN_PLAY_THROUGH><a
   href="#canplaythrough">CAN_PLAY_THROUGH</a></code> and the user agent has
   reached a point in the <a href="#media8">media resource</a> where the user
   has to make a selection for the resource to continue.

  <p>It is possible for a <a href="#media5">media element</a> to have both <a
   href="#ended">ended playback</a> and <a href="#paused0">paused for user
   interaction</a> at the same time.

  <p>When a <a href="#media5">media element</a> is <a
   href="#actively">actively playing</a>, its <a href="#current">current
   playback position</a> must increase monotonically at <code
   title=dom-media-playbackRate><a
   href="#playbackrate">playbackRate</a></code> units of media time per unit
   time of wall clock time. If this value is not 1, the user agent may apply
   pitch adjustments to any audio component of the <a href="#media8">media
   resource</a>.

  <p><a href="#media8" title="media resource">Media resources</a> might be
   internally scripted or interactive. Thus, a <a href="#media5">media
   element</a> could play in a non-linear fashion. If this happens, the user
   agent must act as if the algorithm for <a href="#seek"
   title=dom-media-seek>seeking</a> was used whenever the <a
   href="#current">current playback position</a> changes in a discontinuous
   fashion (so that the relevant events fire).

  <p>When a <a href="#media5">media element</a> that is <a
   href="#actively">actively playing</a> stops playing because its <code
   title=dom-media-readyState><a href="#readystate">readyState</a></code>
   attribute changes to a value lower than <code title=dom-media-CAN_PLAY><a
   href="#canplay">CAN_PLAY</a></code>, without the element having <a
   href="#ended">ended playback</a>, or playback having <a
   href="#stopped">stopped due to errors</a>, or playback having <a
   href="#paused0">paused for user interaction</a>, the user agent must <a
   href="#firing2">fire a simple event</a> called <code
   title=event-timeupdate><a href="#timeupdate">timeupdate</a></code> at the
   element, and then must <a href="#firing2">fire a simple event</a> called
   <code title=event-waiting><a href="#waiting">waiting</a></code> at the
   element.

  <p>When a <a href="#media5">media element</a> that is <a
   href="#actively">actively playing</a> stops playing because it has <a
   href="#paused0">paused for user interaction</a>, the user agent must <a
   href="#firing2">fire a simple event</a> called <code
   title=event-timeupdate><a href="#timeupdate">timeupdate</a></code> at the
   element.

  <p>When <code title=dom-media-currentLoop><a
   href="#currentloop">currentLoop</a></code> is less than <span><code
   title=dom-media-loopCount><a
   href="#loopcount0">loopCount</a></code>-1</span> and the <a
   href="#current">current playback position</a> reaches the <var><a
   href="#effective1">effective loop end</a></var>, then the user agent must
   <a href="#seek" title=dom-media-seek>seek</a> to the <var><a
   href="#effective0">effective loop start</a></var>, increase <code
   title=dom-media-loopCount><a href="#loopcount0">loopCount</a></code> by 1,
   and <a href="#firing2">fire a simple event</a> called <code
   title=event-timeupdate><a href="#timeupdate">timeupdate</a></code>.

  <p>When <code title=dom-media-currentLoop><a
   href="#currentloop">currentLoop</a></code> is equal to the <span><code
   title=dom-media-loopCount><a
   href="#loopcount0">loopCount</a></code>-1</span> and the <a
   href="#current">current playback position</a> reaches the <var><a
   href="#effective2">effective end</a></var>, then the user agent must
   follow these steps:

  <ol>
   <li>
    <p>The user agent must stop playback.

   <li>
    <p>The <code title=dom-media-ended><a href="#ended0">ended</a></code>
     attribute becomes true, as described below.

   <li>
    <p>The user agent must <a href="#firing2">fire a simple event</a> called
     <code title=event-timeupdate><a href="#timeupdate">timeupdate</a></code>
     at the element.

   <li>
    <p>The user agent must <a href="#firing2">fire a simple event</a> called
     <code title=event-ended><a href="#ended1">ended</a></code> at the
     element.
  </ol>

  <p>The <dfn id=defaultplaybackrate
   title=dom-media-defaultPlaybackRate><code>defaultPlaybackRate</code></dfn>
   attribute gives the desired speed at which the <a href="#media8">media
   resource</a> is to play, as a multiple of its intrinsic speed. The
   attribute is mutable, but on setting, if the new value is 0.0, a
   <code>NOT_SUPPORTED_ERR</code> exception must be raised instead of the
   value being changed. It must initially have the value 1.0.

  <p>The <dfn id=playbackrate
   title=dom-media-playbackRate><code>playbackRate</code></dfn> attribute
   gives the speed at which the <a href="#media8">media resource</a> plays,
   as a multiple of its intrinsic speed. If it is not equal to the <code
   title=dom-media-defaultPlaybackRate><a
   href="#defaultplaybackrate">defaultPlaybackRate</a></code>, then the
   implication is that the user is using a feature such as fast forward or
   slow motion playback. The attribute is mutable, but on setting, if the new
   value is 0.0, a <code>NOT_SUPPORTED_ERR</code> exception must be raised
   instead of the value being changed. Otherwise, the playback must change
   speed (if the element is <a href="#actively">actively playing</a>). It
   must initially have the value 1.0.

  <p>When the <code title=dom-media-defaultPlaybackRate><a
   href="#defaultplaybackrate">defaultPlaybackRate</a></code> or <code
   title=dom-media-playbackRate><a
   href="#playbackrate">playbackRate</a></code> attributes change value
   (either by being set by script or by being changed directly by the user
   agent, e.g. in response to user control) the user agent must, once any
   running scripts have finished, <a href="#firing2">fire a simple event</a>
   called <code title=event-ratechange>ratechange</code> at the <a
   href="#media5">media element</a>.

  <p>When the <dfn id=play title=dom-media-play><code>play()</code></dfn>
   method on a <a href="#media5">media element</a> is invoked, the user agent
   must run the following steps.

  <ol>
   <li>
    <p>If the <a href="#media5">media element</a>'s <code
     title=dom-media-networkState><a
     href="#networkstate">networkState</a></code> attribute has the value <a
     href="#empty" title=dom-media-EMPTY>EMPTY</a>, then the user agent must
     sychronously invoke the <code title=dom-media-load><a
     href="#load">load()</a></code> method. If that raises an exception, that
     exception must be reraised by the <code title=dom-media-play><a
     href="#play">play()</a></code> method.

   <li>
    <p>If the <a href="#ended" title="ended playback">playback has ended</a>,
     then the user agent must set <code title=dom-media-currentLoop><a
     href="#currentloop">currentLoop</a></code> to zero and <a href="#seek"
     title=dom-media-seek>seek</a> to the <var><a href="#effective">effective
     start</a></var>.</p>

   <li>
    <p>The <code title=dom-media-playbackRate><a
     href="#playbackrate">playbackRate</a></code> attribute must be set to
     the value of the <code title=dom-media-defaultPlaybackRate><a
     href="#defaultplaybackrate">defaultPlaybackRate</a></code> attribute.

   <li>
    <p>If the <a href="#media5">media element</a>'s <code
     title=dom-media-paused><a href="#paused">paused</a></code> attribute is
     true, it must be set to false.

   <li>
    <p>The <a href="#media5">media element</a>'s <a
     href="#autoplaying">autoplaying flag</a> must be set to false.

   <li>
    <p>The method must then return.
  </ol>

  <p class=note>If the second step above involved a seek, the user agent will
   <a href="#firing2">fire a simple event</a> called <code
   title=event-timeupdate><a href="#timeupdate">timeupdate</a></code> at the
   <a href="#media5">media element</a>.

  <p class=note>If the third step above caused the <code
   title=dom-media-playbackRate><a
   href="#playbackrate">playbackRate</a></code> attribute to change value,
   the user agent will <a href="#firing2">fire a simple event</a> called
   <code title=event-ratechange>ratechange</code> at the <a
   href="#media5">media element</a>.

  <ul>
   <li>
    <p>If the fourth step above changed the value of <code
     title=dom-media-paused><a href="#paused">paused</a></code>, the user
     agent must <a href="#firing2">fire a simple event</a> called <code
     title=event-play><a href="#play0">play</a></code> at the <a
     href="#media5">media element</a>.
  </ul>

  <p>When the <dfn id=pause0 title=dom-media-pause><code>pause()</code></dfn>
   method is invoked, the user agent must run the following steps:

  <ol>
   <li>
    <p>If the <a href="#media5">media element</a>'s <code
     title=dom-media-networkState><a
     href="#networkstate">networkState</a></code> attribute has the value <a
     href="#empty" title=dom-media-EMPTY>EMPTY</a>, then the user agent must
     sychronously invoke the <code title=dom-media-load><a
     href="#load">load()</a></code> method. If that raises an exception, that
     exception must be reraised by the <code title=dom-media-play><a
     href="#play">play()</a></code> method.

   <li>
    <p>If the <a href="#media5">media element</a>'s <code
     title=dom-media-paused><a href="#paused">paused</a></code> attribute is
     false, it must be set to true.

   <li>
    <p>The <a href="#media5">media element</a>'s <a
     href="#autoplaying">autoplaying flag</a> must be set to false.

   <li>
    <p>The method must then return.

   <li>
    <p>If the second step above changed the value of <code
     title=dom-media-paused><a href="#paused">paused</a></code>, the user
     agent must first <a href="#firing2">fire a simple event</a> called <code
     title=event-timeupdate><a href="#timeupdate">timeupdate</a></code> at
     the element, and then <a href="#firing2">fire a simple event</a> called
     title="event-pause">pause at the element.
  </ol>

  <p>The <dfn id=ended0 title=dom-media-ended><code>ended</code></dfn>
   attribute must return true if the <a href="#media5">media element</a> has
   <a href="#ended">ended playback</a>, and false otherwise.

  <p>The <dfn id=played title=dom-media-played><code>played</code></dfn>
   attribute must return a static <a href="#normalised">normalised
   <code>TimeRanges</code> object</a> that represents the ranges of the <a
   href="#media8">media resource</a>, if any, that the user agent has so far
   rendered, at the time the attribute is evaluated.

  <h5 id=seeking><span class=secno>3.14.9.8. </span>Seeking</h5>

  <p>The <dfn id=seeking0 title=dom-media-seeking><code>seeking</code></dfn>
   attribute must initially have the value false.

  <p>When the user agent is required to <dfn id=seek
   title=dom-media-seek>seek</dfn> to a particular <var title="">new playback
   position</var> in the <a href="#media8">media resource</a>, it means that
   the user agent must run the following steps:

  <ol>
   <li>
    <p>If the <a href="#media5">media element</a>'s <code
     title=dom-media-networkState><a
     href="#networkstate">networkState</a></code> is less than <code
     title=dom-media-LOADED_METADATA><a
     href="#loadedmetadata">LOADED_METADATA</a></code>, then the user agent
     must raise an <code>INVALID_STATE_ERR</code> exception (if the seek was
     in response to a DOM method call or setting of a DOM attribute), and
     abort these steps.

   <li>
    <p>If <code title=dom-media-currentLoop><a
     href="#currentloop">currentLoop</a></code> is 0, let <var
     title="">min</var> be the <var><a href="#effective">effective
     start</a></var>. Otherwise, let it be the <var><a
     href="#effective0">effective loop start</a></var>.

   <li>
    <p>If <code title=dom-media-currentLoop><a
     href="#currentloop">currentLoop</a></code> is equal to the value of
     <code title=dom-media-loopCount><a
     href="#loopcount0">loopCount</a></code>, let <var title="">max</var> be
     the <var><a href="#effective2">effective end</a></var>. Otherwise, let
     it be the <var><a href="#effective1">effective loop end</a></var>.

   <li>
    <p>If the <var title="">new playback position</var> is more than <var
     title="">max</var>, let it be <var title="">max</var>.

   <li>
    <p>If the <var title="">new playback position</var> is less than <var
     title="">min</var>, let it be <var title="">min</var>.

   <li>
    <p>If the (possibly now changed) <var title="">new playback
     position</var> is not in one of the ranges given in the <code
     title=dom-media-seekable><a href="#seekable">seekable</a></code>
     attribute, then the user agent must raise an <code>INDEX_SIZE_ERR</code>
     exception (if the seek was in response to a DOM method call or setting
     of a DOM attribute), and abort these steps.

   <li>
    <p>The <a href="#current">current playback position</a> must be set to
     the given <var title="">new playback position</var>.

   <li>
    <p>The <code title=dom-media-seeking><a
     href="#seeking0">seeking</a></code> DOM attribute must be set to true.

   <li>
    <p>The user agent must <a href="#firing2">fire a simple event</a> called
     <code title=event-timeupdate><a href="#timeupdate">timeupdate</a></code>
     at the element.

   <li>
    <p>As soon as the user agent has established whether or not the <a
     href="#media7">media data</a> for the <var title="">new playback
     position</var> is available, and, if it is, decoded enough data to play
     back that position, the <code title=dom-media-seeking><a
     href="#seeking0">seeking</a></code> DOM attribute must be set to false.
  </ol>

  <p>The <dfn id=seekable
   title=dom-media-seekable><code>seekable</code></dfn> attribute must return
   a static <a href="#normalised">normalised <code>TimeRanges</code>
   object</a> that represents the ranges of the <a href="#media8">media
   resource</a>, if any, that the user agent is able to seek to, at the time
   the attribute is evaluated, notwithstanding the looping attributes (i.e.
   the <var><a href="#effective">effective start</a></var> and <var><a
   href="#effective2">effective end</a></var>, etc, don't affect the <code
   title=dom-media-seekable><a href="#seekable">seeking</a></code>
   attribute).

  <p class=note>If the user agent can seek to anywhere in the <a
   href="#media8">media resource</a>, e.g. because the user agent and the
   server support HTTP Range requests, then the attribute would return an
   object with one range, whose start is 0, and whose end is the same as the
   <code title=dom-media-duration><a href="#duration">duration</a></code>
   attribute's value.

  <h5 id=cue-points><span class=secno>3.14.9.9. </span>Cue points</h5>

  <p><a href="#media5" title="media element">Media elements</a> have an
   ordered list of (<var title="">time</var>, <var title="">callback</var>)
   tuples called the <dfn id=cue-point>cue point list</dfn>. Each entry in
   the list also has a boolean <var title="">pause</var> associated with it.

  <p>The <dfn id=addcuepoint
   title=dom-media-addCuePoint><code>addCuePoint(<var title="">time</var>,
   <var title="">callback</var>, <var title="">pause</var>)</code></dfn>
   method must, when called, add a tuple made of the given <var
   title="">time</var> and <var title="">callback</var> to the element's <a
   href="#cue-point">cue point list</a>, and associate with that entry the
   value of the <var title="">pause</var> argument.

  <p>The <dfn id=removecuepoint
   title=dom-media-removeCuePoint><code>removeCuePoint(<var
   title="">time</var>, <var title="">callback</var>)</code></dfn> method
   must, when called, remove the first tuple matching the given <var
   title="">time</var> and <var title="">callback</var> from the element's <a
   href="#cue-point">cue point list</a>.

  <p>When the <a href="#current">current playback position</a> of a <a
   href="#media5">media element</a> reaches one of the times given in the
   element's <a href="#cue-point">cue point list</a>, the user agent must
   follow these steps:

  <ol>
   <li>
    <p>First, if any of the entries in the <a href="#cue-point">cue point
     list</a> with that time have their associated <var title="">pause</var>
     boolean set to true, then the user agent must immediately act as if the
     element's <code title=dom-media-pause><a
     href="#pause0">pause()</a></code> method had been invoked.

   <li>
    <p>The user agent must then <a href="#firing2">fire a simple event</a>
     called <code title=event-timeupdate><a
     href="#timeupdate">timeupdate</a></code> at the element.

   <li>
    <p>The user agent must then invoke all the non-null callbacks for all the
     entries in the list that match the <a href="#current">current playback
     position</a> time, in the order they were added to the list.
  </ol>

  <p>Invoking a callback (an object implementing the <code><a
   href="#voidcallback">VoidCallback</a></code> interface) means calling its
   <code title=dom-VoidCallback-handleEvent><a
   href="#handleevent">handleEvent()</a></code> method.

  <pre class=idl>interface <dfn id=voidcallback>VoidCallback</dfn> {
  void <a href="#handleevent" title=dom-voidCallback-handleEvent>handleEvent</a>();
};</pre>

  <p>The <dfn id=handleevent
   title=dom-voidCallback-handleEvent><code>handleEvent</code></dfn> method
   of objects implementing the <code><a
   href="#voidcallback">VoidCallback</a></code> interface is the entrypoint
   for the callback represented by the object.

  <p>In the ECMAScript DOM binding, the ECMAScript native
   <code>Function</code> type must implement the <code><a
   href="#voidcallback">VoidCallback</a></code> interface such that invoking
   the <code>handleEvent()</code> method of that interface on the object from
   another language binding invokes the function itself. In the ECMAScript
   binding itself, however, the <code>handleEvent()</code> method of the
   interface is not directly accessible on <code>Function</code> objects.
   Such functions, when invoked, must be called at the scope of the <a
   href="#browsing0">browsing context</a>.</p>
  <!--
  XXX if you change this make sure to also look up the other mentions
  of handleEvent() in this file -->

  <h5 id=user-interface><span class=secno>3.14.9.10. </span>User interface</h5>

  <p>The <dfn id=controls
   title=attr-media-controls><code>controls</code></dfn> attribute is a <a
   href="#boolean0">boolean attribute</a>. If the attribute is present, or if
   <a href="#scripting1">scripting is disabled</a>, then the user agent
   should <dfn id=expose>expose a user interface to the user</dfn>. This user
   interface should include features to begin playback, pause playback, seek
   to an arbitrary position in the content (if the content supports arbitrary
   seeking), change the volume, and showe the media content in manners more
   suitable to the user (e.g. full-screen video or in an independent
   resizable window). Other controls may also be made available.

  <p>If the attribute is absent, then the user agent should avoid making a
   user interface available that could conflict with an author-provided user
   interface. User agents may make the following features available, however,
   even when the attribute is absent:

  <p>User agents may provide controls to affect playback of the media
   resource (e.g. play, pause, seeking, and volume controls), but such
   features should not interfere with the page's normal rendering. For
   example, such features could be exposed in the <a href="#media5">media
   element</a>'s context menu.

  <p>Where possible (specifically, for starting, stopping, pausing, and
   unpausing playback, for muting or changing the volume of the audio, and
   for seeking), user interface features exposed by the user agent must be
   implemented in terms of the DOM API described above, so that, e.g., all
   the same events fire.

  <p>The <dfn id=controls0
   title=dom-media-controls><code>controls</code></dfn> DOM attribute must <a
   href="#reflect">reflect</a> the content attribute of the same name.

  <p>The <dfn id=volume title=dom-media-volume><code>volume</code></dfn>
   attribute must return the playback volume of any audio portions of the <a
   href="#media5">media element</a>, in the range 0.0 (silent) to 1.0
   (loudest). Initially, the volume must be 0.5, but user agents may remember
   the last set value across sessions, on a per-site basis or otherwise, so
   the volume may start at other values. On setting, if the new value is in
   the range 0.0 to 1.0 inclusive, the attribute must be set to the new value
   and the playback volume must be correspondingly adjusted as soon as
   possible after setting the attribute, with 0.0 being silent, and 1.0 being
   the loudest setting, values in between increasing in loudness. The range
   need not be linear. The loudest setting may be lower than the system's
   loudest possible setting; for example the user could have set a maximum
   volume. If the new value is outside the range 0.0 to 1.0 inclusive, then,
   on setting, an <code>INDEX_SIZE_ERR</code> exception must be raised
   instead.

  <p>The <dfn id=muted title=dom-media-muted><code>muted</code></dfn>
   attribute must return true if the audio channels are muted and false
   otherwise. On setting, the attribute must be set to the new value; if the
   new value is true, audio playback for this <a href="#media8">media
   resource</a> must then be muted, and if false, audio playback must then be
   enabled.

  <p>Whenever either the <code title=dom-media-muted><a
   href="#muted">muted</a></code> or <code title=dom-media-volume><a
   href="#volume">volume</a></code> attributes are changed, after any running
   scripts have finished executing, the user agent must <a
   href="#firing2">fire a simple event</a> called <code
   title=event-volumechange><a href="#volumechange">volumechange</a></code>
   at the <a href="#media5">media element</a>.

  <h5 id=time-range><span class=secno>3.14.9.11. </span>Time range</h5>

  <p>Objects implementing the <code><a
   href="#timeranges">TimeRanges</a></code> interface represent a list of
   ranges (periods) of time.

  <pre class=idl>interface <dfn id=timeranges>TimeRanges</dfn> {
  readonly attribute unsigned long <a href="#length3" title=dom-TimeRanges-length>length</a>;
  float <a href="#start4" title=dom-TimeRanges-start>start</a>(in unsigned long index);
  float <a href="#endindex" title=dom-TimeRanges-end>end</a>(in unsigned long index);
};</pre>

  <p>The <dfn id=length3
   title=dom-TimeRanges-length><code>length</code></dfn> DOM attribute must
   return the number of ranges represented by the object.

  <p>The <dfn id=start4 title=dom-TimeRanges-start><code>start(<var
   title="">index</var>)</code></dfn> method must return the position of the
   start of the <var title="">index</var>th range represented by the object,
   in seconds measured from the start of the timeline that the object covers.

  <p>The <dfn id=endindex title=dom-TimeRanges-end><code>end(<var
   title="">index</var>)</code></dfn> method must return the position of the
   end of the <var title="">index</var>th range represented by the object, in
   seconds measured from the start of the timeline that the object covers.

  <p>When a <code><a href="#timeranges">TimeRanges</a></code> object is said
   to be a <dfn id=normalised>normalised <code>TimeRanges</code>
   object</dfn>, the ranges it represents must obey the following criteria:

  <ul>
   <li>The start of a range must be greater than the end of all earlier
    ranges.

   <li>The start of a range must be less than the end of that same range.
  </ul>

  <p>In other words, the ranges in such an object are ordered, don't overlap,
   and don't touch (adjacent ranges are folded into one bigger range).

  <p>The timelines used by the objects returned by the <code
   title=dom-media-buffered><a href="#buffered">buffered</a></code>, <code
   title=dom-media-seekable><a href="#seekable">seekable</a></code> and <code
   title=dom-media-played><a href="#played">played</a></code> DOM attributes
   of <a href="#media5" title="media element">media elements</a> must be the
   same as that element's <a href="#media8">media resource</a>'s timeline.

  <h5 id=mediaevents><span class=secno>3.14.9.12. </span>Event summary</h5>

  <p>The following events fire on <a href="#media5" title="media
   element">media elements</a> as part of the processing model described
   above:

  <table>
   <thead>
    <tr>
     <th>Event name

     <th>Interface

     <th>Dispatched when...

     <th>Preconditions

   <tbody>
    <tr>
     <td><dfn id=begin title=event-begin><code>begin</code></dfn>

     <td><code>ProgressEvent</code> <a href="#refsPROGRESS">[PROGRESS]</a>

     <td>The user agent begins fetching the <a href="#media7">media data</a>,
      synchronously during the <code title=dom-media-load><a
      href="#load">load()</a></code> method call.

     <td><code title=dom-media-networkState><a
      href="#networkstate">networkState</a></code> equals <code
      title=dom-media-LOADING><a href="#loading0">LOADING</a></code>

    <tr>
     <td><dfn id=progress0 title=event-progress><code>progress</code></dfn>

     <td><code>ProgressEvent</code> <a href="#refsPROGRESS">[PROGRESS]</a>

     <td>The user agent is fetching <a href="#media7">media data</a>.

     <td><code title=dom-media-networkState><a
      href="#networkstate">networkState</a></code> is more than <code
      title=dom-media-EMPTY><a href="#empty">EMPTY</a></code> and less than
      <code title=dom-media-LOADED><a href="#loaded">LOADED</a></code>

    <tr>
     <td><dfn id=loadedmetadata0
      title=event-loadedmetadata><code>loadedmetadata</code></dfn>

     <td><code>Event</code>

     <td>The user agent is fetching <a href="#media7">media data</a>, and the
      <a href="#media8">media resource</a>'s metadata has just been received.
      

     <td><code title=dom-media-networkState><a
      href="#networkstate">networkState</a></code> equals <code
      title=dom-media-LOADED_METADATA><a
      href="#loadedmetadata">LOADED_METADATA</a></code>

    <tr>
     <td><dfn id=loadedfirstframe0
      title=event-loadedfirstframe><code>loadedfirstframe</code></dfn>

     <td><code>Event</code>

     <td>The user agent is fetching <a href="#media7">media data</a>, and the
      <a href="#media8">media resource</a>'s metadata has just been received.
      

     <td><code title=dom-media-networkState><a
      href="#networkstate">networkState</a></code> equals <code
      title=dom-media-LOADED_FIRST_FRAME><a
      href="#loadedfirstframe">LOADED_FIRST_FRAME</a></code>

    <tr>
     <td><dfn id=load0 title=event-load><code>load</code></dfn>

     <td><code>ProgressEvent</code> <a href="#refsPROGRESS">[PROGRESS]</a>

     <td>The user agent finishes downloading the entire <a
      href="#media8">media resource</a>.

     <td><code title=dom-media-networkState><a
      href="#networkstate">networkState</a></code> equals <code
      title=dom-media-LOADED><a href="#loaded">LOADED</a></code>

    <tr>
     <td><dfn id=abort title=event-abort><code>abort</code></dfn>

     <td><code>ProgressEvent</code> <a href="#refsPROGRESS">[PROGRESS]</a>

     <td>The user agent stops fetching the <a href="#media7">media data</a>
      before it is completely downloaded. This can be fired synchronously
      during the <code title=dom-media-load><a href="#load">load()</a></code>
      method call.

     <td><code title=dom-media-error><a href="#error0">error</a></code> is an
      object with the code <code title=dom-MediaError-MEDIA_ERR_ABORTED><a
      href="#mediaerraborted">MEDIA_ERR_ABORTED</a></code>. <code
      title=dom-media-networkState><a
      href="#networkstate">networkState</a></code> equals either <code
      title=dom-media-EMPTY><a href="#empty">EMPTY</a></code> or <code
      title=dom-media-LOADED><a href="#loaded">LOADED</a></code>, depending
      on when the download was aborted.

    <tr>
     <td><dfn id=error1 title=event-error><code>error</code></dfn>

     <td><code>ProgressEvent</code> <a href="#refsPROGRESS">[PROGRESS]</a>

     <td>An error occurs while fetching the <a href="#media7">media data</a>.
      

     <td><code title=dom-media-error><a href="#error0">error</a></code> is an
      object with the code <code
      title=dom-MediaError-MEDIA_ERR_NETWORK_ERROR>MEDIA_ERR_NETWORK_ERROR</code>
      or higher. <code title=dom-media-networkState><a
      href="#networkstate">networkState</a></code> equals either <code
      title=dom-media-EMPTY><a href="#empty">EMPTY</a></code> or <code
      title=dom-media-LOADED><a href="#loaded">LOADED</a></code>, depending
      on when the download was aborted.

    <tr>
     <td><dfn id=emptied title=event-emptied><code>emptied</code></dfn>

     <td><code>Event</code>

     <td>A <a href="#media5">media element</a> whose <code
      title=dom-media-networkState><a
      href="#networkstate">networkState</a></code> was previously not in the
      <code title=dom-media-EMPTY><a href="#empty">EMPTY</a></code> state has
      just switched to that state (either because of a fatal error during
      load that's about to be reported, or because the <code
      title=dom-media-load><a href="#load">load()</a></code> method was
      reinvoked, in which case it is fired synchronously during the <code
      title=dom-media-load><a href="#load">load()</a></code> method call).

     <td><code title=dom-media-networkState><a
      href="#networkstate">networkState</a></code> is <code
      title=dom-media-EMPTY><a href="#empty">EMPTY</a></code>; all the DOM
      attributes are in their initial states.

    <tr>
     <td><dfn id=stalled title=event-stalled><code>stalled</code></dfn>

     <td><code>ProgressEvent</code>

     <td>The user agent is trying to fetch <a href="#media7">media data</a>,
      but data is unexpectedly not forthcoming.

     <td>

    <tr>
     <td><dfn id=play0 title=event-play><code>play</code></dfn>

     <td><code>Event</code>

     <td>Playback has begun. Fired after the <code title=dom-media-play><a
      href="#play">play</a></code> method has returned.

     <td><code title=dom-media-paused><a href="#paused">paused</a></code> is
      newly false.

    <tr>
     <td><dfn id=pause1 title=event-pause><code>pause</code></dfn>

     <td><code>Event</code>

     <td>Playback has been paused. Fired after the <code
      title=dom-media-pause><a href="#pause0">pause</a></code> method has
      returned.

     <td><code title=dom-media-paused><a href="#paused">paused</a></code> is
      newly true.

    <tr>
     <td><dfn id=waiting title=event-waiting><code>waiting</code></dfn>

     <td><code>Event</code>

     <td>Playback has stopped because the next frame is not available, but
      the user agent expects that frame to become available in due course.

     <td><code title=dom-media-readyState><a
      href="#readystate">readyState</a></code> is either <code
      title=dom-media-DATA_UNAVAILABLE><a
      href="#dataunavailable">DATA_UNAVAILABLE</a></code> or <code
      title=dom-media-CAN_SHOW_CURRENT_FRAME><a
      href="#canshowcurrentframe">CAN_SHOW_CURRENT_FRAME</a></code>, and
      <code title=dom-media-paused><a href="#paused">paused</a></code> is
      false. Either <code title=dom-media-seeking><a
      href="#seeking0">seeking</a></code> is true, or the <a
      href="#current">current playback position</a> is not contained in any
      of the ranges in <code title=dom-media-buffered><a
      href="#buffered">buffered</a></code>. It is possible for playback to
      stop for two other reasons without <code title=dom-media-paused><a
      href="#paused">paused</a></code> being false, but those two reasons do
      not fire this event: maybe <a href="#ended" title="ended
      playback">playback ended</a>, or playback <a href="#stopped">stopped
      due to errors</a>.

    <tr>
     <td><dfn id=timeupdate
      title=event-timeupdate><code>timeupdate</code></dfn>

     <td><code>Event</code>

     <td>The <a href="#current">current playback position</a> changed in an
      interesting way, for example discontinuously.

     <td>

    <tr>
     <td><dfn id=ended1 title=event-ended><code>ended</code></dfn>

     <td><code>Event</code>

     <td>Playback has stopped because the end of the <a href="#media8">media
      resource</a> was reached.

     <td><code title=dom-media-currentTime><a
      href="#currenttime">currentTime</a></code> equals the <var><a
      href="#effective2">effective end</a></var>; <code
      title=dom-media-ended><a href="#ended0">ended</a></code> is true.

    <tr>
     <td><dfn id=dataunavailable0
      title=event-dataunavailable><code>dataunavailable</code></dfn>

     <td><code>Event</code>

     <td>The user agent cannot render the data at the <a
      href="#current">current playback position</a> because data for the
      current frame is not immediately available.

     <td>The <code title=dom-media-readyState><a
      href="#readystate">readyState</a></code> attribute is newly equal to
      <code title=DATA_UNAVAILABLE>DATA_UNAVAILABLE</code>.

    <tr>
     <td><dfn id=canshowcurrentframe0
      title=event-canshowcurrentframe><code>canshowcurrentframe</code></dfn>

     <td><code>Event</code>

     <td>The user agent cannot render the data after the <a
      href="#current">current playback position</a> because data for the next
      frame is not immediately available.

     <td>The <code title=dom-media-readyState><a
      href="#readystate">readyState</a></code> attribute is newly equal to
      <code title=CAN_SHOW_CURRENT_FRAME>CAN_SHOW_CURRENT_FRAME</code>.

    <tr>
     <td><dfn id=canplay0 title=event-canplay><code>canplay</code></dfn>

     <td><code>Event</code>

     <td>The user agent can resume playback of the <a href="#media7">media
      data</a>, but estimates that if playback were to be started now, the <a
      href="#media8">media resource</a> could not be rendered at the current
      playback rate up to its end without having to stop for further
      buffering of content.

     <td>The <code title=dom-media-readyState><a
      href="#readystate">readyState</a></code> attribute is newly equal to
      <code title=CAN_PLAY>CAN_PLAY</code>.

    <tr>
     <td><dfn id=canplaythrough0
      title=event-canplaythrough><code>canplaythrough</code></dfn>

     <td><code>Event</code>

     <td>The user agent estimates that if playback were to be started now,
      the <a href="#media8">media resource</a> could be rendered at the
      current playback rate all the way to its end without having to stop for
      further buffering.

     <td>The <code title=dom-media-readyState><a
      href="#readystate">readyState</a></code> attribute is newly equal to
      <code title=CAN_PLAY_THROUGH>CAN_PLAY_THROUGH</code>.

    <tr>
     <td><dfn id=ratechange
      title=event-ratehange><code>ratechange</code></dfn>

     <td><code>Event</code>

     <td>Either the <code title=dom-media-defaultPlaybackRate><a
      href="#defaultplaybackrate">defaultPlaybackRate</a></code> or the <code
      title=dom-media-playbackRate><a
      href="#playbackrate">playbackRate</a></code> attribute has just been
      updated.

     <td>

    <tr>
     <td><dfn id=durationchange
      title=event-durationchange><code>durationchange</code></dfn>

     <td><code>Event</code>

     <td>The <code title=dom-media-duration><a
      href="#duration">duration</a></code> attribute has just been updated.

     <td>

    <tr>
     <td><dfn id=volumechange
      title=event-volumechange><code>volumechange</code></dfn>

     <td><code>Event</code>

     <td>Either the <code title=dom-media-volume><a
      href="#volume">volume</a></code> attribute or the <code
      title=dom-media-muted><a href="#muted">muted</a></code> attribute has
      changed. Fired after the relevant attribute's setter has returned.

     <td>
  </table>

  <h5 id=security0><span class=secno>3.14.9.13. </span>Security and privacy
   considerations</h5>

  <p class=big-issue>Talk about making sure interactive media files (e.g.
   SVG) don't have access to the container DOM (XSS potential); talk about
   not exposing any sensitive data like metadata from tracks in the media
   files (intranet snooping risk)

  <h4 id=the-source><span class=secno>3.14.10. </span>The <dfn
   id=source><code>source</code></dfn> element</h4>
  <!-- no type -->

  <dl class=element>
   <dt>Contexts in which this element may be used:

   <dd>As a child of a <a href="#media5">media element</a>, before any
    content other than <code><a href="#source">source</a></code> elements.

   <dt>Content model:

   <dd>Empty.

   <dt>Element-specific attributes:

   <dd><code title=attr-source-src><a href="#src7">src</a></code> (required)

   <dd><code title=attr-source-type><a href="#type8">type</a></code>

   <dd><code title=attr-source-media><a href="#media9">media</a></code>

   <dt>DOM interface:

   <dd>
    <pre
     class=idl>interface <dfn id=htmlsourceelement>HTMLSourceElement</dfn> : <a href="#htmlelement">HTMLElement</a> {
           attribute DOMString <a href="#src8" title=dom-source-src>src</a>;
           attribute DOMString <a href="#type9" title=dom-source-type>type</a>;
           attribute DOMString <a href="#media10" title=dom-source-media>media</a>;
};</pre>
  </dl>

  <p>The <code><a href="#source">source</a></code> element allows authors to
   specify multiple <a href="#media8" title="media resource">media
   resources</a> for <a href="#media5" title="media element">media
   elements</a>.

  <p>The <dfn id=src7 title=attr-source-src><code>src</code></dfn> attribute
   gives the address of the <a href="#media8">media resource</a>. The value
   must be a URI (or IRI). This attribute must be present.

  <p>The <dfn id=type8 title=attr-source-type><code>type</code></dfn>
   attribute gives the type of the <a href="#media8">media resource</a>, to
   help the user agent determine if it can play this <a href="#media8">media
   resource</a> before downloading it. Its value must be a MIME type. The
   <code title="">codec</code> parameter may be specified and might be
   necessary to specify exactly how the resource is encoded. <a
   href="#refsRFC2046">[RFC2046]</a> <a href="#refsRFC4281">[RFC4281]</a>

  <p>The <dfn id=media9 title=attr-source-media><code>media</code></dfn>
   attribute gives the intended media type of the <a href="#media8">media
   resource</a>, to help the user agent determine if this <a
   href="#media8">media resource</a> is useful to the user before downloading
   it. Its value must be a valid media query. <a href="#refsMQ">[MQ]</a>

  <p>Either the <code title=attr-source-type><a href="#type8">type</a></code>
   attribute, the <code title=attr-source-media><a
   href="#media9">media</a></code> attribute or both, must be specified,
   unless this is the last <code><a href="#source">source</a></code> element
   child of the parent element.

  <p>If a <code><a href="#source">source</a></code> element is inserted into
   a <a href="#media5">media element</a> that is already in a document and
   whose <code title=dom-media-networkState><a
   href="#networkstate">networkState</a></code> is in the <code
   title=dom-media-EMPTY><a href="#empty">EMPTY</a></code> state, the user
   agent must implicitly invoke the <code title=dom-media-load><a
   href="#load">load()</a></code> method on the <a href="#media5">media
   element</a> as soon as all other scripts have finished executing. Any
   exceptions raised must be ignored.

  <p>The DOM attributes <dfn id=src8
   title=dom-source-src><code>src</code></dfn>, <dfn id=type9
   title=dom-source-type><code>type</code></dfn>, and <dfn id=media10
   title=dom-source-media><code>media</code></dfn> must <a
   href="#reflect">reflect</a> the respective content attributes of the same
   name.

  <h4 id=the-canvas><span class=secno>3.14.11. </span>The <dfn
   id=canvas><code>canvas</code></dfn> element</h4>

  <p><a href="#strictly" title="Strictly inline-level content">Strictly
   inline-level</a> <a href="#embedded0">embedded content</a>.

  <dl class=element>
   <dt>Contexts in which this element may be used:

   <dd>As the only <a href="#embedded0">embedded content</a> child of a
    <code><a href="#figure">figure</a></code> element.

   <dd>Where <a href="#strictly">strictly inline-level content</a> is
    allowed.

   <dt>Content model:

   <dd><a href="#inline-level0">Inline-level content</a>.

   <dt>Element-specific attributes:

   <dd><code title=attr-canvas-height><a href="#height3">height</a></code>

   <dd><code title=attr-canvas-width><a href="#width3">width</a></code>

   <dt>DOM interface:

   <dd>
    <pre
     class=idl>interface <dfn id=htmlcanvaselement>HTMLCanvasElement</dfn> : <a href="#htmlelement">HTMLElement</a> {
         attribute unsigned long <a href="#width4" title=dom-canvas-width>width</a>;
         attribute unsigned long <a href="#height4" title=dom-canvas-height>height</a>;

  DOMString <a href="#todataurl" title=dom-canvas-toDataURL>toDataURL</a>();
  DOMString <a href="#todataurl0" title=dom-canvas-toDataURL-type>toDataURL</a>(in DOMString type);

  DOMObject <a href="#getcontext" title=dom-canvas-getContext>getContext</a>(in DOMString contextId);
};</pre>
  </dl>

  <p class=big-issue>Shouldn't allow inline-level content to be the content
   model when the parent's content model is strictly inline only.

  <p>The <code><a href="#canvas">canvas</a></code> element represents a
   resolution-dependent bitmap canvas, which can be used for rendering
   graphs, game graphics, or other visual images on the fly.

  <p>Authors should not use the <code><a href="#canvas">canvas</a></code>
   element in a document when a more suitable element is available. For
   example, it is inappropriate to use a <code><a
   href="#canvas">canvas</a></code> element to render a page heading: if the
   desired presentation of the heading is graphically intense, it should be
   marked up using appropriate elements (typically <code><a
   href="#h1">h1</a></code>) and then styled using CSS and supporting
   technologies such as XBL.

  <p>When authors use the <code><a href="#canvas">canvas</a></code> element,
   they should also provide content that, when presented to the user, conveys
   essentially the same function or purpose as the bitmap canvas. This
   content may be placed as content of the <code><a
   href="#canvas">canvas</a></code> element. The contents of the <code><a
   href="#canvas">canvas</a></code> element, if any, are the element's <a
   href="#fallback">fallback content</a>.

  <p>In interactive visual media with <span>scripting enabled</span>, the
   canvas element is an embedded element with a dynamically created image.

  <p>In non-interactive, static, visual media, if the <code><a
   href="#canvas">canvas</a></code> element has been previously painted on
   (e.g. if the page was viewed in an interactive visual medium and is now
   being printed, or if some script that ran during the page layout process
   painted on the element), then the <code><a
   href="#canvas">canvas</a></code> element must be treated as embedded
   content with the current image and size. Otherwise, the element's fallback
   content must be used instead.

  <p>In non-visual media, and in visual media with <span>scripting
   disabled</span>, the <code><a href="#canvas">canvas</a></code> element's
   fallback content must be used instead.

  <p>The <code><a href="#canvas">canvas</a></code> element has two attributes
   to control the size of the coordinate space: <dfn id=height3
   title=attr-canvas-height><code>height</code></dfn> and <dfn id=width3
   title=attr-canvas-width><code>width</code></dfn>. These attributes, when
   specified, must have values that are <a href="#valid" title="valid
   non-negative integer">valid non-negative integers</a>. The <a
   href="#rules">rules for parsing non-negative integers</a> must be used to
   obtain their numeric values. If an attribute is missing, or if parsing its
   value returns an error, then the default value must be used instead. The
   <code title=attr-canvas-width><a href="#width3">width</a></code> attribute
   defaults to 300, and the <code title=attr-canvas-height><a
   href="#height3">height</a></code> attribute defaults to 150.

  <p>The intrinsic dimensions of the <code><a
   href="#canvas">canvas</a></code> element equal the size of the coordinate
   space, with the numbers interpreted in CSS pixels. However, the element
   can be sized arbitrarily by a style sheet. During rendering, the image is
   scaled to fit this layout size.

  <p>The size of the coordinate space does not necessarily represent the size
   of the actual bitmap that the user agent will use internally or during
   rendering. On high-definition displays, for instance, the user agent may
   internally use a bitmap with two device pixels per unit in the coordinate
   space, so that the rendering remains at high quality throughout.

  <p>The canvas must initially be fully transparent black.

  <p>Whenever the <code title=attr-canvas-width><a
   href="#width3">width</a></code> and <code title=attr-canvas-height><a
   href="#height3">height</a></code> attributes are set (whether to a new
   value or to the previous value), the bitmap and any associated contexts
   must be cleared back to their initial state and reinitialised with the
   newly specified coordinate space dimensions.

  <p>The <dfn id=width4 title=dom-canvas-width><code>width</code></dfn> and
   <dfn id=height4 title=dom-canvas-height><code>height</code></dfn> DOM
   attributes must <a href="#reflect">reflect</a> the content attributes of
   the same name.

  <div class=example>
   <p>Only one square appears to be drawn in the following example:</p>

   <pre>
  // canvas is a reference to a &lt;canvas> element
  var context = canvas.getContext('2d');
  context.fillRect(0,0,50,50);
  canvas.setAttribute('width', '300'); // clears the canvas
  context.fillRect(0,100,50,50);
  canvas.width = canvas.width; // clears the canvas
  context.fillRect(100,0,50,50); // only this square remains</pre>
  </div>

  <p>To draw on the canvas, authors must first obtain a reference to a <dfn
   id=context0>context</dfn> using the <dfn id=getcontext
   title=dom-canvas-getContext><code>getContext(<var
   title="">contextId</var>)</code></dfn> method of the <code><a
   href="#canvas">canvas</a></code> element.

  <p>This specification only defines one context, with the name "<code
   title=canvas-context-2d><a href="#d">2d</a></code>". If <code
   title=dom-canvas-getContext><a href="#getcontext">getContext()</a></code>
   is called with that exact string for tis <var title="">contextId</var>
   argument, then the UA must return a reference to an object implementing
   <code><a
   href="#canvasrenderingcontext2d">CanvasRenderingContext2D</a></code>.
   Other specifications may define their own contexts, which would return
   different objects.

  <p>Vendors may also define experimental contexts using the syntax
   <code><var title="">vendorname</var>-<var title="">context</var></code>,
   for example, <code>moz-3d</code>.

  <p>When the UA is passed an empty string or a string specifying a context
   that it does not support, then it must return null. String comparisons
   must be literal and case-sensitive.

  <p class=note>A future version of this specification will probably define a
   <code>3d</code> context (probably based on the OpenGL ES API).

  <p>The <dfn id=todataurl
   title=dom-canvas-toDataURL><code>toDataURL()</code></dfn> method must,
   when called with no arguments, return a <code title="">data:</code> URI
   containing a representation of the image as a PNG file. <a
   href="#refsPNG">[PNG]</a>.

  <p>The <dfn id=todataurl0
   title=dom-canvas-toDataURL-type><code>toDataURL(<var
   title="">type</var>)</code></dfn> method (when called with one <em>or
   more</em> arguments) must return a <code>data:</code> URI containing a
   representation of the image in the format given by <var
   title="">type</var>. The possible values are MIME types with no
   parameters, for example <code>image/png</code>, <code>image/jpeg</code>,
   or even maybe <code>image/svg+xml</code> if the implementation actually
   keeps enough information to reliably render an SVG image from the canvas.

  <p>Only support for <code>image/png</code> is required. User agents may
   support other types. If the user agent does not support the requested
   type, it must return the image using the PNG format.

  <p>User agents must convert the provided type to lower case before
   establishing if they support that type and before creating the
   <code>data:</code> URI.</p>
  <!-- XXX define "convert to lower case"
  -->

  <p class=note>When trying to use types other than <code>image/png</code>,
   authors can check if the image was really returned in the requested format
   by checking to see if the returned string starts with one the exact
   strings "<code title="">data:image/png,</code>" or "<code
   title="">data:image/png;</code>". If it does, the image is PNG, and thus
   the requested type was not supported.

  <p>Arguments other than the <var title="">type</var> must be ignored, and
   must not cause the user agent to raise an exception (as would normally
   occur if a method was called with the wrong number of arguments). A future
   version of this specification will probably allow extra parameters to be
   passed to <code title=dom-canvas-toDataURL><a
   href="#todataurl">toDataURL()</a></code> to allow authors to more
   carefully control compression settings, image metadata, etc.

  <p><strong>Security:</strong> To prevent <em>information leakage</em>, the
   <code title=dom-canvas-toDataURL><a
   href="#todataurl">toDataURL()</a></code> and <code
   title=dom-context-2d-getImageData><a
   href="#getimagedata">getImageData()</a></code> methods should raise a <a
   href="#security8">security exception</a> if the canvas has ever had an
   image painted on it whose <a href="#origin0">origin</a> is different from
   that of the script calling the method.

  <h5 id=the-2d><span class=secno>3.14.11.1. </span>The 2D context</h5>

  <p>When the <code title=dom-canvas-getContext><a
   href="#getcontext">getContext()</a></code> method of a <code><a
   href="#canvas">canvas</a></code> element is invoked with <dfn id=d
   title=canvas-context-2d><code>2d</code></dfn> as the argument, a <code><a
   href="#canvasrenderingcontext2d">CanvasRenderingContext2D</a></code>
   object is returned.

  <p>There is only one <code><a
   href="#canvasrenderingcontext2d">CanvasRenderingContext2D</a></code>
   object per canvas, so calling the <code title=dom-canvas-getContext><a
   href="#getcontext">getContext()</a></code> method with the <code
   title=canvas-context-2d><a href="#d">2d</a></code> argument a second time
   must return the same object.

  <p>The 2D context represents a flat cartesian surface whose origin (0,0) is
   at the top left corner, with the coordinate space having <var
   title="">x</var> values increasing when going right, and <var
   title="">y</var> values increasing when going down.

  <pre
   class=idl>interface <dfn id=canvasrenderingcontext2d>CanvasRenderingContext2D</dfn> {

  // back-reference to the canvas
  readonly attribute <a href="#htmlcanvaselement">HTMLCanvasElement</a> <a href="#canvas0" title=dom-context-2d-canvas>canvas</a>;

  // state
  void <a href="#save" title=dom-context-2d-save>save</a>(); // push state on state stack
  void <a href="#restore" title=dom-context-2d-restore>restore</a>(); // pop state stack and restore state

  // transformations (default transform is the identity matrix)
  void <a href="#scale" title=dom-context-2d-scale>scale</a>(in float x, in float y);
  void <a href="#rotate" title=dom-context-2d-rotate>rotate</a>(in float angle);
  void <a href="#translate" title=dom-context-2d-translate>translate</a>(in float x, in float y);
  void <a href="#transform" title=dom-context-2d-transform>transform</a>(in float m11, in float m12, in float m21, in float m22, in float dx, in float dy);
  void <a href="#settransform" title=dom-context-2d-setTransform>setTransform</a>(in float m11, in float m12, in float m21, in float m22, in float dx, in float dy);
<!--
  // XXXv3 we've also received requests for:
  void skew(...);
  void reflect(...); // or mirror(...)
-->
  // compositing
           attribute float <a href="#globalalpha" title=dom-context-2d-globalAlpha>globalAlpha</a>; // (default 1.0)
           attribute DOMString <a href="#globalcompositeoperation" title=dom-context-2d-globalCompositeOperation>globalCompositeOperation</a>; // (default source-over)

  // colors and styles
           attribute DOMObject <a href="#strokestyle" title=dom-context-2d-strokeStyle>strokeStyle</a>; // (default black)
           attribute DOMObject <a href="#fillstyle" title=dom-context-2d-fillStyle>fillStyle</a>; // (default black)
  <a href="#canvasgradient0">CanvasGradient</a> <a href="#createlineargradient" title=dom-context-2d-createLinearGradient>createLinearGradient</a>(in float x0, in float y0, in float x1, in float y1);
  <a href="#canvasgradient0">CanvasGradient</a> <a href="#createradialgradient" title=dom-context-2d-createRadialGradient>createRadialGradient</a>(in float x0, in float y0, in float r0, in float x1, in float y1, in float r1);
  <a href="#canvaspattern0">CanvasPattern</a> <a href="#createpatternimage" title=dom-context-2d-createPattern>createPattern</a>(in <a href="#htmlimageelement">HTMLImageElement</a> image, DOMString repetition);
  <a href="#canvaspattern0">CanvasPattern</a> <a href="#createpatternimage" title=dom-context-2d-createPattern>createPattern</a>(in <a href="#htmlcanvaselement">HTMLCanvasElement</a> image, DOMString repetition);

  // line caps/joins
           attribute float <a href="#linewidth" title=dom-context-2d-lineWidth>lineWidth</a>; // (default 1)
           attribute DOMString <a href="#linecap" title=dom-context-2d-lineCap>lineCap</a>; // "butt", "round", "square" (default "butt")
           attribute DOMString <a href="#linejoin" title=dom-context-2d-lineJoin>lineJoin</a>; // "round", "bevel", "miter" (default "miter")
           attribute float <a href="#miterlimit" title=dom-context-2d-miterLimit>miterLimit</a>; // (default 10)

  // shadows
           attribute float <a href="#shadowoffsetx" title=dom-context-2d-shadowOffsetX>shadowOffsetX</a>; // (default 0)
           attribute float <a href="#shadowoffsety" title=dom-context-2d-shadowOffsetY>shadowOffsetY</a>; // (default 0)
           attribute float <a href="#shadowblur" title=dom-context-2d-shadowBlur>shadowBlur</a>; // (default 0)
           attribute DOMString <a href="#shadowcolor" title=dom-context-2d-shadowColor>shadowColor</a>; // (default transparent black)

  // rects
  void <a href="#clearrect" title=dom-context-2d-clearRect>clearRect</a>(in float x, in float y, in float w, in float h);
  void <a href="#fillrect" title=dom-context-2d-fillRect>fillRect</a>(in float x, in float y, in float w, in float h);
  void <a href="#strokerect" title=dom-context-2d-strokeRect>strokeRect</a>(in float x, in float y, in float w, in float h);

  // path API
  void <a href="#beginpath" title=dom-context-2d-beginPath>beginPath</a>();
  void <a href="#closepath" title=dom-context-2d-closePath>closePath</a>();
  void <a href="#moveto" title=dom-context-2d-moveTo>moveTo</a>(in float x, in float y);
  void <a href="#lineto" title=dom-context-2d-lineTo>lineTo</a>(in float x, in float y);
  void <a href="#quadraticcurveto" title=dom-context-2d-quadraticCurveTo>quadraticCurveTo</a>(in float cpx, in float cpy, in float x, in float y);
  void <a href="#beziercurveto" title=dom-context-2d-bezierCurveTo>bezierCurveTo</a>(in float cp1x, in float cp1y, in float cp2x, in float cp2y, in float x, in float y);
  void <a href="#arcto" title=dom-context-2d-arcTo>arcTo</a>(in float x1, in float y1, in float x2, in float y2, in float radius);
  void <a href="#rectx" title=dom-context-2d-rect>rect</a>(in float x, in float y, in float w, in float h);
  void <a href="#arcx-" title=dom-context-2d-arc>arc</a>(in float x, in float y, in float radius, in float startAngle, in float endAngle, in boolean anticlockwise);
  void <a href="#fill" title=dom-context-2d-fill>fill</a>();
  void <a href="#stroke" title=dom-context-2d-stroke>stroke</a>();
  void <a href="#clip" title=dom-context-2d-clip>clip</a>();
  boolean <a href="#ispointinpath" title=dom-context-2d-isPointInPath>isPointInPath</a>(in float x, in float y);

  // drawing images
  void <a href="#drawimage" title=dom-context-2d-drawImage>drawImage</a>(in <a href="#htmlimageelement">HTMLImageElement</a> image, in float dx, in float dy);
  void <a href="#drawimage" title=dom-context-2d-drawImage>drawImage</a>(in <a href="#htmlimageelement">HTMLImageElement</a> image, in float dx, in float dy, in float dw, in float dh);
  void <a href="#drawimage" title=dom-context-2d-drawImage>drawImage</a>(in <a href="#htmlimageelement">HTMLImageElement</a> image, in float sx, in float sy, in float sw, in float sh, in float dx, in float dy, in float dw, in float dh);
  void <a href="#drawimage" title=dom-context-2d-drawImage>drawImage</a>(in <a href="#htmlcanvaselement">HTMLCanvasElement</a> image, in float dx, in float dy);
  void <a href="#drawimage" title=dom-context-2d-drawImage>drawImage</a>(in <a href="#htmlcanvaselement">HTMLCanvasElement</a> image, in float dx, in float dy, in float dw, in float dh);
  void <a href="#drawimage" title=dom-context-2d-drawImage>drawImage</a>(in <a href="#htmlcanvaselement">HTMLCanvasElement</a> image, in float sx, in float sy, in float sw, in float sh, in float dx, in float dy, in float dw, in float dh);

  // pixel manipulation
  <a href="#imagedata">ImageData</a> <a href="#getimagedata" title=dom-context-2d-getImageData>getImageData</a>(in float sx, in float sy, in float sw, in float sh);
  void <a href="#putimagedata" title=dom-context-2d-putImageData>putImageData</a>(in <a href="#imagedata">ImageData</a> image, in float dx, in float dy);

  // drawing text is not supported in this version of the API
  // (there is no way to predict what metrics the fonts will have,
  // which makes fonts very hard to use for painting)

};

interface <dfn id=canvasgradient>CanvasGradient</dfn> {
  // opaque object
  void <a href="#addcolorstop" title=dom-canvasgradient-addColorStop>addColorStop</a>(in float offset, in DOMString color);
};

interface <dfn id=canvaspattern>CanvasPattern</dfn> {
  // opaque object
};

interface <dfn id=imagedata>ImageData</dfn> {
  readonly attribute long int <a href="#width5" title=dom-imagedata-width>width</a>;
  readonly attribute long int <a href="#height5" title=dom-imagedata-height>height</a>;
  readonly attribute int[] <a href="#data1" title=dom-imagedata-data>data</a>;
};</pre>

  <p>The <dfn id=canvas0
   title=dom-context-2d-canvas><code>canvas</code></dfn> attribute must
   return the <code><a href="#canvas">canvas</a></code> element that the
   context paints on.

  <h6 id=the-canvas0><span class=secno>3.14.11.1.1. </span>The canvas state</h6>

  <p>Each context maintains a stack of drawing states. <dfn id=drawing0
   title="drawing state">Drawing states</dfn> consist of:

  <ul class=brief>
   <li>The current transformation matrix.

   <li>The current clip region.

   <li>The current values of the following attributes: <code
    title=dom-context-2d-strokeStyle><a
    href="#strokestyle">strokeStyle</a></code>, <code
    title=dom-context-2d-fillStyle><a href="#fillstyle">fillStyle</a></code>,
    <code title=dom-context-2d-globalAlpha><a
    href="#globalalpha">globalAlpha</a></code>, <code
    title=dom-context-2d-lineWidth><a href="#linewidth">lineWidth</a></code>,
    <code title=dom-context-2d-lineCap><a href="#linecap">lineCap</a></code>,
    <code title=dom-context-2d-lineJoin><a
    href="#linejoin">lineJoin</a></code>, <code
    title=dom-context-2d-miterLimit><a
    href="#miterlimit">miterLimit</a></code>, <code
    title=dom-context-2d-shadowOffsetX><a
    href="#shadowoffsetx">shadowOffsetX</a></code>, <code
    title=dom-context-2d-shadowOffsetY><a
    href="#shadowoffsety">shadowOffsetY</a></code>, <code
    title=dom-context-2d-shadowBlur><a
    href="#shadowblur">shadowBlur</a></code>, <code
    title=dom-context-2d-shadowColor><a
    href="#shadowcolor">shadowColor</a></code>, <code
    title=dom-context-2d-globalCompositeOperation><a
    href="#globalcompositeoperation">globalCompositeOperation</a></code>.
  </ul>

  <p class=note>The current path and the current bitmap are not part of the
   drawing state. The current path is persistent, and can only be reset using
   the <code title=dom-context-2d-beginPath><a
   href="#beginpath">beginPath()</a></code> method. The current bitmap is
   <span title=concept-canvas-image>a property of the
   canvas</span><!-- XXX xref -->, not the context.

  <p>The <dfn id=save title=dom-context-2d-save><code>save()</code></dfn>
   method must push a copy of the current drawing state onto the drawing
   state stack.

  <p>The <dfn id=restore
   title=dom-context-2d-restore><code>restore()</code></dfn> method must pop
   the top entry in the drawing state stack, and reset the drawing state it
   describes. If there is no saved state, the method must do nothing.

  <h6 id=transformations><span class=secno>3.14.11.1.2. </span><dfn
   id=transformations0>Transformations</dfn></h6>

  <p>The transformation matrix is applied to all drawing operations prior to
   their being rendered. It is also applied when creating the clip region.</p>
  <!-- conformance criteria for actual drawing are
  described in "drawing model" below -->

  <p>When the context is created, the transformation matrix must initially be
   the identity transform. It may then be adjusted using the transformation
   methods.

  <p>The transformation matrix can become infinite, at which point nothing is
   drawn anymore.</p>
  <!--
   Philip Taylor wrote:
   > My experience with some 3d canvas code is that infinities come up in
   > naturally harmless places, e.g. having a function that scales by x then
   > translates by 1/x and wanting it to work when x=0 (which ought to draw
   > nothing, since anything it draws is zero pixels wide), and it's a bit
   > annoying to track down and fix those issues, so I'd probably like it if
   > they were harmless in canvas methods. Opera appears to silently not draw
   > anything if the transformation matrix is not finite, but Firefox throws
   > exceptions when passing in non-finite arguments.
  -->

  <p>The transformations must be performed in reverse order. For instance, if
   a scale transformation that doubles the width is applied, followed by a
   rotation transformation that rotates drawing operations by a quarter turn,
   and a rectangle twice as wide as it is tall is then drawn on the canvas,
   the actual result will be a square.

  <p>The <dfn id=scale title=dom-context-2d-scale><code>scale(<var
   title="">x</var>, <var title="">y</var>)</code></dfn> method must add the
   scaling transformation described by the arguments to the transformation
   matrix. The <var title="">x</var> argument represents the scale factor in
   the horizontal direction and the <var title="">y</var> argument represents
   the scale factor in the vertical direction. The factors are multiples. If
   either argument is Infinity the transformation matrix must be marked as
   infinite instead of the method throwing an exception.

  <p>The <dfn id=rotate title=dom-context-2d-rotate><code>rotate(<var
   title="">angle</var>)</code></dfn> method must add the rotation
   transformation described by the argument to the transformation matrix. The
   <var title="">angle</var> argument represents a clockwise rotation angle
   expressed in radians.

  <p>The <dfn id=translate
   title=dom-context-2d-translate><code>translate(<var title="">x</var>, <var
   title="">y</var>)</code></dfn> method must add the translation
   transformation described by the arguments to the transformation matrix.
   The <var title="">x</var> argument represents the translation distance in
   the horizontal direction and the <var title="">y</var> argument represents
   the translation distance in the vertical direction. The arguments are in
   coordinate space units. If either argument is Infinity the transformation
   matrix must be marked as infinite instead of the method throwing an
   exception.

  <p>The <dfn id=transform
   title=dom-context-2d-transform><code>transform(<var title="">m11</var>,
   <var title="">m12</var>, <var title="">m21</var>, <var title="">m22</var>,
   <var title="">dx</var>, <var title="">dy</var>)</code></dfn> method must
   multiply the current transformation matrix with the matrix described by:

  <table class=matrix>
   <tbody>
    <tr>
     <td><var title="">m11</var>

     <td><var title="">m21</var>

     <td><var title="">dx</var>

    <tr>
     <td><var title="">m12</var>

     <td><var title="">m22</var>

     <td><var title="">dy</var>

    <tr>
     <td>0

     <td>0

     <td>1
  </table>

  <p>If any of the arguments are Infinity the transformation matrix must be
   marked as infinite instead of the method throwing an exception.

  <p>The <dfn id=settransform
   title=dom-context-2d-setTransform><code>setTransform(<var
   title="">m11</var>, <var title="">m12</var>, <var title="">m21</var>, <var
   title="">m22</var>, <var title="">dx</var>, <var
   title="">dy</var>)</code></dfn> method must reset the current transform to
   the identity matrix, and then invoke the <code><a href="#transform"
   title=dom-context-2d-transform>transform</a>(<var title="">m11</var>, <var
   title="">m12</var>, <var title="">m21</var>, <var title="">m22</var>, <var
   title="">dx</var>, <var title="">dy</var>)</code> method with the same
   arguments. If any of the arguments are Infinity the transformation matrix
   must be marked as infinite instead of the method throwing an exception.

  <h6 id=compositing><span class=secno>3.14.11.1.3. </span>Compositing</h6>

  <p>All drawing operations are affected by the global compositing
   attributes, <code title=dom-context-2d-globalAlpha><a
   href="#globalalpha">globalAlpha</a></code> and <code
   title=dom-context-2d-globalCompositeOperation><a
   href="#globalcompositeoperation">globalCompositeOperation</a></code>.</p>
  <!-- conformance criteria for painting are described in the "drawing
  model" section below -->

  <p>The <dfn id=globalalpha
   title=dom-context-2d-globalAlpha><code>globalAlpha</code></dfn> attribute
   gives an alpha value that is applied to shapes and images before they are
   composited onto the canvas. The value must be in the range from 0.0 (fully
   transparent) to 1.0 (no additional transparency). If an attempt is made to
   set the attribute to a value outside this range, the attribute must retain
   its previous value. When the context is created, the <code
   title=dom-context-2d-globalAlpha><a
   href="#globalalpha">globalAlpha</a></code> attribute must initially have
   the value 1.0.

  <p>The <dfn id=globalcompositeoperation
   title=dom-context-2d-globalCompositeOperation><code>globalCompositeOperation</code></dfn>
   attribute sets how shapes and images are drawn onto the existing bitmap,
   once they have had <code title=dom-context-2d-globalAlpha><a
   href="#globalalpha">globalAlpha</a></code> and the current transformation
   matrix applied. It must be set to a value from the following list. In the
   descriptions below, the source image, <var title="">A</var>, is the shape
   or image being rendered, and the destination image, <var title="">B</var>,
   is the current state of the bitmap.

  <dl>
   <dt><dfn id=source-atop
    title=gcop-source-atop><code>source-atop</code></dfn>

   <dd><var title="">A</var> atop <var title="">B</var>. Display the source
    image wherever both images are opaque. Display the destination image
    wherever the destination image is opaque but the source image is
    transparent. Display transparency elsewhere.

   <dt><dfn id=source-in title=gcop-source-in><code>source-in</code></dfn>

   <dd><var title="">A</var> in <var title="">B</var>. Display the source
    image wherever both the source image and destination image are opaque.
    Display transparency elsewhere.

   <dt><dfn id=source-out title=gcop-source-out><code>source-out</code></dfn>

   <dd><var title="">A</var> out <var title="">B</var>. Display the source
    image wherever the source image is opaque and the destination image is
    transparent. Display transparency elsewhere.

   <dt><dfn id=source-over
    title=gcop-source-over><code>source-over</code></dfn> (default)

   <dd><var title="">A</var> over <var title="">B</var>. Display the source
    image wherever the source image is opaque. Display the destination image
    elsewhere.

   <dt><dfn id=destination-atop
    title=gcop-destination-atop><code>destination-atop</code></dfn>

   <dd><var title="">B</var> atop <var title="">A</var>. Same as <code
    title=gcop-source-atop><a href="#source-atop">source-atop</a></code> but
    using the destination image instead of the source image and vice versa.

   <dt><dfn id=destination-in
    title=gcop-destination-in><code>destination-in</code></dfn>

   <dd><var title="">B</var> in <var title="">A</var>. Same as <code
    title=gcop-source-in><a href="#source-in">source-in</a></code> but using
    the destination image instead of the source image and vice versa.

   <dt><dfn id=destination-out
    title=gcop-destination-out><code>destination-out</code></dfn>

   <dd><var title="">B</var> out <var title="">A</var>. Same as <code
    title=gcop-source-out><a href="#source-out">source-out</a></code> but
    using the destination image instead of the source image and vice versa.

   <dt><dfn id=destination-over
    title=gcop-destination-over><code>destination-over</code></dfn>

   <dd><var title="">B</var> over <var title="">A</var>. Same as <code
    title=gcop-source-over><a href="#source-over">source-over</a></code> but
    using the destination image instead of the source image and vice versa.</dd>
   <!-- no clear definition of this operator (doesn't correspond to a PorterDuff operator)
   <dt><dfn title="gcop-darker"><code>darker</code></dfn></dt>

   <dd>Display the sum of the source image and destination image,
   with color values approaching 0 as a limit.</dd>
-->

   <dt><dfn id=lighter title=gcop-lighter><code>lighter</code></dfn>

   <dd><var title="">A</var> plus <var title="">B</var>. Display the sum of
    the source image and destination image, with color values approaching 1
    as a limit.

   <dt><dfn id=copy title=gcop-copy><code>copy</code></dfn>

   <dd><var title="">A</var> (<var title="">B</var> is ignored). Display the
    source image instead of the destination image.

   <dt><dfn id=xor title=gcop-xor><code>xor</code></dfn>

   <dd><var title="">A</var> xor <var title="">B</var>. Exclusive OR of the
    source image and destination image.

   <dt><code><var title="">vendorName</var>-<var
    title="">operationName</var></code>

   <dd>Vendor-specific extensions to the list of composition operators should
    use this syntax.
  </dl>

  <p>These values are all case-sensitive &mdash; they must be used exactly as
   shown. User agents must only recognise values that exactly match the
   values given above.

  <p>The operators in the above list must be treated as described by the
   Porter-Duff operator given at the start of their description (e.g. <var
   title="">A</var> over <var title="">B</var>). <a
   href="#refsPORTERDUFF">[PORTERDUFF]</a></p>
  <!--
        <dd id="refsPORTERDUFF">[PORTERDUFF]</dd>
        <dd><cite>Compositing Digital Images</cite>, SIGGRAPH '84: Proceedings of the 11th annual conference on Computer graphics and interactive techniques, Volume 18, Number 3, T. Porter, T Duff. ACM Press, July 1984. ISBN 0-89791-138-5.</dd>
  -->

  <p>On setting, if the user agent does not recognise the specified value, it
   must be ignored, leaving the value of <code
   title=dom-context-2d-globalCompositeOperation><a
   href="#globalcompositeoperation">globalCompositeOperation</a></code>
   unaffected.

  <p>When the context is created, the <code
   title=dom-context-2d-globalCompositeOperation><a
   href="#globalcompositeoperation">globalCompositeOperation</a></code>
   attribute must initially have the value <code>source-over</code>.

  <h6 id=colors><span class=secno>3.14.11.1.4. </span>Colors and styles</h6>

  <p>The <dfn id=strokestyle
   title=dom-context-2d-strokeStyle><code>strokeStyle</code></dfn> attribute
   represents the color or style to use for the lines around shapes, and the
   <dfn id=fillstyle
   title=dom-context-2d-fillStyle><code>fillStyle</code></dfn> attribute
   represents the color or style to use inside the shapes.

  <p>Both attributes can be either strings, <code><a
   href="#canvasgradient0">CanvasGradient</a></code>s, or <code><a
   href="#canvaspattern0">CanvasPattern</a></code>s. On setting, strings must
   be parsed as CSS &lt;color&gt; values and the color assigned, and <code><a
   href="#canvasgradient0">CanvasGradient</a></code> and <code><a
   href="#canvaspattern0">CanvasPattern</a></code> objects must be assigned
   themselves. <a href="#refsCSS3COLOR">[CSS3COLOR]</a> If the value is a
   string but is not a valid color, or is neither a string, a <code><a
   href="#canvasgradient0">CanvasGradient</a></code>, nor a <code><a
   href="#canvaspattern0">CanvasPattern</a></code>, then it must be ignored,
   and the attribute must retain its previous value.

  <p>On getting, if the value is a color, then: if it has alpha equal to 1.0,
   then the color must be returned as a lowercase six-digit hex value,
   prefixed with a "#" character (U+0023 NUMBER SIGN), with the first two
   digits representing the red component, the next two digits representing
   the green component, and the last two digits representing the blue
   component, the digits being in the range 0-9 a-f (U+0030 to U+0039 and
   U+0061 to U+0066). If the value has alpha less than 1.0, then the value
   must instead be returned in the CSS <code title="">rgba()</code>
   functional-notation format: the literal string <code title="">rgba</code>
   (U+0072 U+0067 U+0062 U+0061) followed by a U+0028 LEFT PARENTHESIS, a
   base-ten integer in the range 0-255 representing the red component (using
   digits 0-9, U+0030 to U+0039, in the shortest form possible), a literal
   U+002C COMMA and U+0020 SPACE, an integer for the green component, a comma
   and a space, an integer for the blue component, another comma and space, a
   U+0030 DIGIT ZERO, a U+002E FULL STOP (representing the decimal point),
   one or more digits in the range 0-9 (U+0030 to U+0039) representing the
   fractional part of the alpha value, and finally a U+0029 RIGHT
   PARENTHESIS.

  <p>Otherwise, if it is not a color but a <code><a
   href="#canvasgradient0">CanvasGradient</a></code> or <code><a
   href="#canvaspattern0">CanvasPattern</a></code>, then the respective
   object must be returned. (Such objects are opaque and therefore only
   useful for assigning to other attributes or for comparison to other
   gradients or patterns.)

  <p>When the context is created, the <code
   title=dom-context-2d-strokeStyle><a
   href="#strokestyle">strokeStyle</a></code> and <code
   title=dom-context-2d-fillStyle><a href="#fillstyle">fillStyle</a></code>
   attributes must initially have the string value <code
   title="">#000000</code>.

  <p>There are two types of gradients, linear gradients and radial gradients,
   both represented by objects implementing the opaque <dfn
   id=canvasgradient0><code>CanvasGradient</code></dfn> interface.

  <p>Once a gradient has been created (see below), stops are placed along it
   to define how the colors are distributed along the gradient. The color of
   the gradient at each stop is the color specified for that stop. Between
   each such stop, the colors and the alpha component must be linearly
   interpolated over the RGBA space without premultiplying the alpha value to
   find the color to use at that offset. Before the first stop, the color
   must be the color of the first stop. After the last stop, the color must
   be the color of the last stop. When there are no stops, the gradient is
   transparent black.

  <p>The <dfn id=addcolorstop
   title=dom-canvasgradient-addColorStop><code>addColorStop(<var
   title="">offset</var>, <var title="">color</var>)</code></dfn> method on
   the <code><a href="#canvasgradient0">CanvasGradient</a></code> interface
   adds a new stop to a gradient. If the <var title="">offset</var> is less
   than 0 or greater than 1 then an <code>INDEX_SIZE_ERR</code> exception
   must be raised. If the <var title="">color</var> cannot be parsed as a CSS
   color, then a <code>SYNTAX_ERR</code> exception must be raised. Otherwise,
   the gradient must have a new stop placed, at offset <var
   title="">offset</var> relative to the whole gradient, and with the color
   obtained by parsing <var title="">color</var> as a CSS &lt;color&gt;
   value. If multiple stops are added at the same offset on a gradient, they
   must be placed in the order added, with the first one closest to the start
   of the gradient, and each subsequent one infinitesimally further along
   towards the end point (in effect causing all but the first and last stop
   added at each point to be ignored).

  <p>The <dfn id=createlineargradient
   title=dom-context-2d-createLinearGradient><code>createLinearGradient(<var
   title="">x0</var>, <var title="">y0</var>, <var title="">x1</var>, <var
   title="">y1</var>)</code></dfn> method takes four arguments, representing
   the start point (<var title="">x0</var>, <var title="">y0</var>) and end
   point (<var title="">x1</var>, <var title="">y1</var>) of the gradient, in
   coordinate space units, and must return a linear <code><a
   href="#canvasgradient0">CanvasGradient</a></code> initialised with that
   line.

  <p>Linear gradients must be rendered such that at and before the starting
   point on the canvas the color at offset 0 is used, that at and after the
   ending point the color at offset 1 is used, and that all points on a line
   perpendicular to the line that crosses the start and end points have the
   color at the point where those two lines cross (with the colors coming
   from the interpolation described above).

  <p>If <span><var title="">x<sub>0</sub></var>&nbsp;=&nbsp;<var
   title="">x<sub>1</sub></var></span> and <span><var
   title="">y<sub>0</sub></var>&nbsp;=&nbsp;<var
   title="">y<sub>1</sub></var></span>, then the linear gradient must paint
   nothing.</p>
  <!-- XXX could make this paint the start colour,
  or the end colour, or raise an exception -->

  <p>The <dfn id=createradialgradient
   title=dom-context-2d-createRadialGradient><code>createRadialGradient(<var
   title="">x0</var>, <var title="">y0</var>, <var title="">r0</var>, <var
   title="">x1</var>, <var title="">y1</var>, <var
   title="">r1</var>)</code></dfn> method takes six arguments, the first
   three representing the start circle with origin (<var title="">x0</var>,
   <var title="">y0</var>) and radius <var title="">r0</var>, and the last
   three representing the end circle with origin (<var title="">x1</var>,
   <var title="">y1</var>) and radius <var title="">r1</var>. The values are
   in coordinate space units. The method must return a radial <code><a
   href="#canvasgradient0">CanvasGradient</a></code> initialised with those
   two circles. If either of <var title="">r0</var> or <var title="">r1</var>
   are negative, an <code>INDEX_SIZE_ERR</code> exception must be raised.

  <p>Radial gradients must be rendered by following these steps:

  <ol>
   <li>
    <p>Let <span>x(<var title="">&omega;</var>)&nbsp;=&nbsp;(<var
     title="">x<sub>1</sub></var>-<var title="">x<sub>0</sub></var>)<var
     title="">&omega;</var>&nbsp;+&nbsp;<var
     title="">x<sub>0</sub></var></span></p>

    <p>Let <span>y(<var title="">&omega;</var>)&nbsp;=&nbsp;(<var
     title="">y<sub>1</sub></var>-<var title="">y<sub>0</sub></var>)<var
     title="">&omega;</var>&nbsp;+&nbsp;<var
     title="">y<sub>0</sub></var></span></p>

    <p>Let <span>r(<var title="">&omega;</var>)&nbsp;=&nbsp;(<var
     title="">r<sub>1</sub></var>-<var title="">r<sub>0</sub></var>)<var
     title="">&omega;</var>&nbsp;+&nbsp;<var
     title="">r<sub>0</sub></var></span></p>

    <p>Let the color at <var title="">&omega;</var> be the color of the
     gradient at offset 0.0 for all values of <var title="">&omega;</var>
     less than 0.0, the color at offset 1.0 for all values of <var
     title="">&omega;</var> greater than 1.0, and the color at the given
     offset for values of <var title="">&omega;</var> in the range
     <span>0.0&nbsp;&le;&nbsp;<var
     title="">&omega;</var>&nbsp;&le;&nbsp;1.0</span>

   <li>
    <p>For all values of <var title="">&omega;</var> where <span>r(<var
     title="">&omega;</var>)&nbsp;&gt;&nbsp;0</span>, starting with the value
     of <var title="">&omega;</var> nearest to positive infinity and ending
     with the value of <var title="">&omega;</var> nearest to negative
     infinity, draw the circumference of the circle with radius <span>r(<var
     title="">&omega;</var>)</span> at position (<span>x(<var
     title="">&omega;</var>)</span>, <span>y(<var
     title="">&omega;</var>)</span>), with the color at <var
     title="">&omega;</var>, but only painting on the parts of the canvas
     that have not yet been painted on by earlier circles in this step for
     this rendering of the gradient.
  </ol>

  <p>If <span><var title="">x<sub>0</sub></var>&nbsp;=&nbsp;<var
   title="">x<sub>1</sub></var></span> and <span><var
   title="">y<sub>0</sub></var>&nbsp;=&nbsp;<var
   title="">y<sub>1</sub></var></span> and <span><var
   title="">r<sub>0</sub></var>&nbsp;=&nbsp;<var
   title="">r<sub>1</sub></var></span>, then the radial gradient must paint
   nothing.</p>
  <!-- XXX could make this paint the start colour,
  or the end colour, or a circle of one in the other, or raise an
  exception -->

  <p class=note>This effectively creates a cone, touched by the two circles
   defined in the creation of the gradient, with the part of the cone before
   the start circle (0.0) using the color of the first offset, the part of
   the cone after the end circle (1.0) using the color of the last offset,
   and areas outside the cone untouched by the gradient (transparent black).

  <p>Gradients must only be painted where the relevant stroking or filling
   effects requires that they be drawn.

  <p>Support for actually painting gradients is optional. Instead of painting
   the gradients, user agents may instead just paint the first stop's color.
   However, <code title=dom-context-2d-createLinearGradient><a
   href="#createlineargradient">createLinearGradient()</a></code> and <code
   title=dom-context-2d-createRadialGradient><a
   href="#createradialgradient">createRadialGradient()</a></code> must always
   return objects when passed valid arguments.

  <p>Patterns are represented by objects implementing the opaque <dfn
   id=canvaspattern0><code>CanvasPattern</code></dfn> interface.

  <p>To create objects of this type, the <dfn id=createpatternimage
   title=dom-context-2d-createPattern><code>createPattern(image,
   repetition)</code></dfn> method is used. The first argument gives the
   image to use as the pattern (either an <code><a
   href="#htmlimageelement">HTMLImageElement</a></code> or an <code><a
   href="#htmlcanvaselement">HTMLCanvasElement</a></code>). Modifying this
   image after calling the <code title=dom-context-2d-createPattern><a
   href="#createpatternimage">createPattern()</a></code> method must not
   affect the pattern. The second argument must be a string with one of the
   following values: <code title="">repeat</code>, <code
   title="">repeat-x</code>, <code title="">repeat-y</code>, <code
   title="">no-repeat</code>. If the empty string or null is specified, <code
   title="">repeat</code> must be assumed. If an unrecognised value is given,
   then the user agent must raise a <code>SYNTAX_ERR</code> exception. User
   agents must recognise the four values described above exactly (e.g. they
   must not do case folding). The method must return a <code><a
   href="#canvaspattern0">CanvasPattern</a></code> object suitably
   initialised.

  <p>The <var title="">image</var> argument must be an instance of an
   <code><a href="#htmlimageelement">HTMLImageElement</a></code> or <code><a
   href="#htmlcanvaselement">HTMLCanvasElement</a></code>. If the <var
   title="">image</var> is of the wrong type, the implementation must raise a
   <code>TYPE_MISMATCH_ERR</code> exception. If the <var title="">image</var>
   argument is an <code><a
   href="#htmlimageelement">HTMLImageElement</a></code> object whose <code
   title=dom-attr-complete>complete</code> attribute is false, then the
   implementation must raise an <code>INVALID_STATE_ERR</code> exception.

  <p>Patterns must be painted so that the top left of the first image is
   anchored at the origin of the coordinate space, and images are then
   repeated horizontally to the left and right (if the <code>repeat-x</code>
   string was specified) or vertically up and down (if the
   <code>repeat-y</code> string was specified) or in all four directions all
   over the canvas (if the <code>repeat</code> string was specified). The
   images are not be scaled by this process; one CSS pixel of the image must
   be painted on one coordinate space unit. Of course, patterns must only
   actually painted where the stroking or filling effect requires that they
   be drawn, and are affected by the current transformation matrix.

  <p>Support for patterns is optional. If the user agent doesn't support
   patterns, then <code title=dom-context-2d-createPattern><a
   href="#createpatternimage">createPattern()</a></code> must return null.</p>
  <!--
   XXXv3 Requests for v3 features:
    * apply transforms to patterns, so you don't have to create
      transformed patterns manually by rendering them to an off-screen
      canvas then using that canvas as the pattern.
  -->

  <h6 id=line-styles><span class=secno>3.14.11.1.5. </span>Line styles</h6>

  <p>The <dfn id=linewidth
   title=dom-context-2d-lineWidth><code>lineWidth</code></dfn> attribute
   gives the default width of lines, in coordinate space units. On setting,
   zero and negative values must be ignored, leaving the value unchanged.

  <p>When the context is created, the <code title=dom-context-2d-lineWidth><a
   href="#linewidth">lineWidth</a></code> attribute must initially have the
   value <code>1.0</code>.

  <p>The <dfn id=linecap
   title=dom-context-2d-lineCap><code>lineCap</code></dfn> attribute defines
   the type of endings that UAs shall place on the end of lines. The three
   valid values are <code>butt</code>, <code>round</code>, and
   <code>square</code>. The <code>butt</code> value means that the end of
   each line is a flat edge perpendicular to the direction of the line. The
   <code>round</code> value means that a semi-circle with the diameter equal
   to the width of the line is then added on to the end of the line. The
   <code>square</code> value means that at the end of each line is a
   rectangle with the length of the line width and the width of half the line
   width, placed flat against the edge perpendicular to the direction of the
   line. On setting, any other value than the literal strings
   <code>butt</code>, <code>round</code>, and <code>square</code> must be
   ignored, leaving the value unchanged.

  <p>When the context is created, the <code title=dom-context-2d-lineCap><a
   href="#linecap">lineCap</a></code> attribute must initially have the value
   <code>butt</code>.

  <p>The <dfn id=linejoin
   title=dom-context-2d-lineJoin><code>lineJoin</code></dfn> attribute
   defines the type of corners that that UAs will place where two lines meet.
   The three valid values are <code>round</code>, <code>bevel</code>, and
   <code>miter</code>.

  <p>On setting, any other value than the literal strings <code>round</code>,
   <code>bevel</code> and <code>miter</code> must be ignored, leaving the
   value unchanged.

  <p>When the context is created, the <code title=dom-context-2d-lineJoin><a
   href="#linejoin">lineJoin</a></code> attribute must initially have the
   value <code>miter</code>.

  <p>The <code>round</code> value means that a filled arc connecting the
   corners on the outside of the join, with the diameter equal to the line
   width, and the origin at the point where the inside edges of the lines
   touch, must be rendered at joins. The <code>bevel</code> value means that
   a filled triangle connecting those two corners with a straight line, the
   third point of the triangle being the point where the lines touch on the
   inside of the join, must be rendered at joins. The <code>miter</code>
   value means that a filled four- or five-sided polygon must be placed at
   the join, with two of the lines being the perpendicular edges of the
   joining lines, and the other two being continuations of the outside edges
   of the two joining lines, as long as required to intersect without going
   over the miter limit.

  <p>The miter length is the distance from the point where the lines touch on
   the inside of the join to the intersection of the line edges on the
   outside of the join. The miter limit ratio is the maximum allowed ratio of
   the miter length to the line width. If the miter limit would be exceeded,
   then a fifth line must be added to the polygon, connecting the two outside
   lines, such that the distance from the inside point of the join to the
   point in the middle of this fifth line is the maximum allowed value for
   the miter length.

  <p>The miter limit ratio can be explicitly set using the <dfn id=miterlimit
   title=dom-context-2d-miterLimit><code>miterLimit</code></dfn> attribute.
   On setting, zero and negative values must be ignored, leaving the value
   unchanged.

  <p>When the context is created, the <code
   title=dom-context-2d-miterLimit><a
   href="#miterlimit">miterLimit</a></code> attribute must initially have the
   value <code>10.0</code>.</p>
  <!-- XXX this section doesn't say what these attributes return or
  what they do on setting. not a big deal; it's pretty obvious. but if
  anyone complains, we'll have to add it -->
  <!--
XXXv3 dashed lines have been requested.  Philip Taylor provides these
notes on what would need to be defined for dashed lines:
> I don't think it's entirely trivial to add, to the detail that's
> necessary in a specification. The common graphics APIs (at least
> Cairo, Quartz and java.awt.Graphics, and any SVG implementation) all
> have dashes specified by passing an array of dash lengths (alternating
> on/off), so that should be alright as long as you define what units
> it's measured in and what happens when you specify an odd number of
> values and how errors are handled and what happens if you update the
> array later. But after that, what does it do when stroking multiple
> subpaths, in terms of offsetting the dashes? When you use strokeRect,
> where is offset 0? Does moveTo reset the offset? How does it interact
> with lineCap/lineJoin? All the potential issues need test cases too,
> and the implementations need to make sure they handle any edge cases
> that the underlying graphics library does differently. (SVG Tiny 1.2
> appears to skip some of the problems by leaving things undefined and
> allowing whatever behaviour the graphics library has.)
  -->

  <h6 id=shadows><span class=secno>3.14.11.1.6. </span><dfn
   id=shadows0>Shadows</dfn></h6>

  <p>All drawing operations are affected by the four global shadow
   attributes. Shadows form part of the source image during composition.

  <p>The <dfn id=shadowcolor
   title=dom-context-2d-shadowColor><code>shadowColor</code></dfn> attribute
   sets the color of the shadow.</p>
  <!-- XXX this section doesn't say what this attributes returns or
  what they do on setting. if anyone complains, we'll have to add
  it. shadowColor is a CSS Color attribute. -->

  <p>When the context is created, the <code
   title=dom-context-2d-shadowColor><a
   href="#shadowcolor">shadowColor</a></code> attribute initially must be
   fully-transparent black.

  <p>The <dfn id=shadowoffsetx
   title=dom-context-2d-shadowOffsetX><code>shadowOffsetX</code></dfn> and
   <dfn id=shadowoffsety
   title=dom-context-2d-shadowOffsetY><code>shadowOffsetY</code></dfn>
   attributes specify the distance that the shadow will be offset in the
   positive horizontal and positive vertical distance respectively. Their
   values are in coordinate space units.</p>
  <!-- XXX we don't define getting/setting -->

  <p>When the context is created, the shadow offset attributes initially have
   the value <code>0</code>.

  <p>The <dfn id=shadowblur
   title=dom-context-2d-shadowBlur><code>shadowBlur</code></dfn> attribute
   specifies the number of coordinate space units that the blurring is to
   cover. On setting, negative numbers must be ignored, leaving the attribute
   unmodified.</p>
  <!-- XXX we don't define getting/setting -->

  <p>When the context is created, the <code
   title=dom-context-2d-shadowBlur><a
   href="#shadowblur">shadowBlur</a></code> attribute must initially have the
   value <code>0</code>.

  <p>Support for shadows is optional. When they are supported, then, when
   shadows are drawn, they must be rendered using the specified color,
   offset, and blur radius.</p>
  <!-- XXX we don't really define what that means -->

  <h6 id=simple><span class=secno>3.14.11.1.7. </span>Simple shapes
   (rectangles)</h6>

  <p>There are three methods that immediately draw rectangles to the bitmap.
   They each take four arguments; the first two give the <var
   title="">x</var> and <var title="">y</var> coordinates of the top left of
   the rectangle, and the second two give the width and height of the
   rectangle, respectively.

  <p>Shapes are painted without affecting the current path, and are subject
   to <span title=dom-context-2d->transformations</span>, <a href="#shadows0"
   title=shadows>shadow effects</a>, <span title=globalAlpha>global
   alpha</span>, <a href="#clipping" title="clipping path">clipping
   paths</a>, and <span title=globalCompositeOperation>global composition
   operators</span>.

  <p>Negative values for width and height must cause the implementation to
   raise an <code>INDEX_SIZE_ERR</code> exception.

  <p>The <dfn id=clearrect
   title=dom-context-2d-clearRect><code>clearRect()</code></dfn> method must
   clear the pixels in the specified rectangle to a fully transparent black,
   erasing any previous image. If either height or width are zero, this
   method has no effect.

  <p>The <dfn id=fillrect
   title=dom-context-2d-fillRect><code>fillRect()</code></dfn> method must
   paint the specified rectangular area using the <code
   title=dom-context-2d-fillStyle><a href="#fillstyle">fillStyle</a></code>.
   If either height or width are zero, this method has no effect.

  <p>The <dfn id=strokerect
   title=dom-context-2d-strokeRect><code>strokeRect()</code></dfn> method
   must draw stroke the path that would be created for the outline of a
   rectangle of the specified size using the <code
   title=dom-context-2d-strokeStyle><a
   href="#strokestyle">strokeStyle</a></code>, <code
   title=dom-context-2d-lineWidth><a href="#linewidth">lineWidth</a></code>,
   <code title=dom-context-2d-lineJoin><a
   href="#linejoin">lineJoin</a></code>, and (if appropriate) <code
   title=dom-context-2d-miterLimit><a
   href="#miterlimit">miterLimit</a></code> attributes. If both height and
   width are zero, this method has no effect, since there is no path to
   stroke (it's a point). If only one of the two is zero, then the method
   will draw a line instead (the path for the outline is just a straight line
   along the non-zero dimension).

  <h6 id=complex><span class=secno>3.14.11.1.8. </span>Complex shapes (paths)</h6>

  <p>The context always has a current path. There is only one current path,
   it is not part of the <span title=dom-context-2d->drawing state</span>.

  <p>A <dfn id=path>path</dfn> has a list of zero or more subpaths. Each
   subpath consists of a list of one or more points, connected by straight or
   curved lines, and a flag indicating whether the subpath is closed or not.
   A closed subpath is one where the last point of the subpath is connected
   to the first point of the subpath by a straight line. Subpaths with fewer
   than two points are ignored when painting the path.

  <p>Initially, the context's path must have zero subpaths.

  <p>The <dfn id=beginpath
   title=dom-context-2d-beginPath><code>beginPath()</code></dfn> method must
   empty the list of subpaths so that the context once again has zero
   subpaths.

  <p>The <dfn id=moveto title=dom-context-2d-moveTo><code>moveTo(<var
   title="">x</var>, <var title="">y</var>)</code></dfn> method must create a
   new subpath with the specified point as its first (and only) point.

  <p>The <dfn id=closepath
   title=dom-context-2d-closePath><code>closePath()</code></dfn> method must
   do nothing if the context has no subpaths. Otherwise, it must mark the
   last subpath as closed, create a new subpath whose first point is the same
   as the previous subpath's first point, and finally add this new subpath to
   the path. (If the last subpath had more than one point in its list of
   points, then this is equivalent to adding a straight line connecting the
   last point back to the first point, thus "closing" the shape, and then
   repeating the last <code title=dom-context-2d-moveTo><a
   href="#moveto">moveTo()</a></code> call.)

  <p>New points and the lines connecting them are added to subpaths using the
   methods described below. In all cases, the methods only modify the last
   subpath in the context's paths.

  <p>The <dfn id=lineto title=dom-context-2d-lineTo><code>lineTo(<var
   title="">x</var>, <var title="">y</var>)</code></dfn> method must do
   nothing if the context has no subpaths. Otherwise, it must connect the
   last point in the subpath to the given point (<var title="">x</var>, <var
   title="">y</var>) using a straight line, and must then add the given point
   (<var title="">x</var>, <var title="">y</var>) to the subpath.

  <p>The <dfn id=quadraticcurveto
   title=dom-context-2d-quadraticCurveTo><code>quadraticCurveTo(<var
   title="">cpx</var>, <var title="">cpy</var>, <var title="">x</var>, <var
   title="">y</var>)</code></dfn> method must do nothing if the context has
   no subpaths. Otherwise it must connect the last point in the subpath to
   the given point (<var title="">x</var>, <var title="">y</var>) by a
   quadratic curve with control point (<var title="">cpx</var>, <var
   title="">cpy</var>), and must then add the given point (<var
   title="">x</var>, <var title="">y</var>) to the subpath.

  <p>The <dfn id=beziercurveto
   title=dom-context-2d-bezierCurveTo><code>bezierCurveTo(<var
   title="">cp1x</var>, <var title="">cp1y</var>, <var title="">cp2x</var>,
   <var title="">cp2y</var>, <var title="">x</var>, <var
   title="">y</var>)</code></dfn> method must do nothing if the context has
   no subpaths. Otherwise, it must connect the last point in the subpath to
   the given point (<var title="">x</var>, <var title="">y</var>) using a
   bezier curve with control points (<var title="">cp1x</var>, <var
   title="">cp1y</var>) and (<var title="">cp2x</var>, <var
   title="">cp2y</var>). Then, it must add the point (<var title="">x</var>,
   <var title="">y</var>) to the subpath.

  <p>The <dfn id=arcto title=dom-context-2d-arcTo><code>arcTo(<var
   title="">x1</var>, <var title="">y1</var>, <var title="">x2</var>, <var
   title="">y2</var>, <var title="">radius</var>)</code></dfn> method must do
   nothing if the context has no subpaths. If the context <em>does</em> have
   a subpath, then the behaviour depends on the arguments and the last point
   in the subpath.

  <p>Let the point (<var title="">x0</var>, <var title="">y0</var>) be the
   last point in the subpath. Let <var title="">The Arc</var> be the shortest
   arc given by circumference of the circle that has one point tangent to the
   line defined by the points (<var title="">x0</var>, <var
   title="">y0</var>) and (<var title="">x1</var>, <var title="">y1</var>),
   another point tangent to the line defined by the points (<var
   title="">x1</var>, <var title="">y1</var>) and (<var title="">x2</var>,
   <var title="">y2</var>), and that has radius <var title="">radius</var>.
   The points at which this circle touches these two lines are called the
   start and end tangent points respectively.

  <p>If the point (<var title="">x2</var>, <var title="">y2</var>) is on the
   line defined by the points (<var title="">x0</var>, <var
   title="">y0</var>) and (<var title="">x1</var>, <var title="">y1</var>)
   then the method must do nothing, as no arc would satisfy the above
   constraints.

  <p>Otherwise, the method must connect the point (<var title="">x0</var>,
   <var title="">y0</var>) to the start tangent point by a straight line,
   then connect the start tangent point to the end tangent point by <var
   title="">The Arc</var>, and finally add the start and end tangent points
   to the subpath.

  <p>Negative or zero values for <var title="">radius</var> must cause the
   implementation to raise an <code>INDEX_SIZE_ERR</code> exception.

  <p>The <dfn id=arcx- title=dom-context-2d-arc><code>arc(<var
   title="">x</var>, <var title="">y</var>, <var title="">radius</var>, <var
   title="">startAngle</var>, <var title="">endAngle</var>, <var
   title="">anticlockwise</var>)</code></dfn> method draws an arc. If the
   context has any subpaths, then the method must add a straight line from
   the last point in the subpath to the start point of the arc. In any case,
   it must draw the arc between the start point of the arc and the end point
   of the arc, and add the start and end points of the arc to the subpath.
   The arc and its start and end points are defined as follows:

  <p>Consider a circle that has its origin at (<var title="">x</var>, <var
   title="">y</var>) and that has radius <var title="">radius</var>. The
   points at <var title="">startAngle</var> and <var title="">endAngle</var>
   along the circle's circumference, measured in radians clockwise from the
   positive x-axis, are the start and end points respectively. The arc is the
   path along the circumference of this circle from the start point to the
   end point, going anti-clockwise if the <var title="">anticlockwise</var>
   argument is true, and clockwise otherwise.

  <p>Negative or zero values for <var title="">radius</var> must cause the
   implementation to raise an <code>INDEX_SIZE_ERR</code> exception.

  <p>The <dfn id=rectx title=dom-context-2d-rect><code>rect(<var
   title="">x</var>, <var title="">y</var>, <var title="">w</var>, <var
   title="">h</var>)</code></dfn> method must create a new subpath containing
   just the four points (<var title="">x</var>, <var title="">y</var>), (<var
   title="">x</var>+<var title="">w</var>, <var title="">y</var>), (<var
   title="">x</var>+<var title="">w</var>, <var title="">y</var>+<var
   title="">h</var>), (<var title="">x</var>, <var title="">y</var>+<var
   title="">h</var>), with those four points connected by straight lines, and
   must then mark the subpath as closed. It must then create a new subpath
   with the point (<var title="">x</var>, <var title="">y</var>) as the only
   point in the subpath.

  <p>Negative values for <var title="">w</var> and <var title="">h</var> must
   cause the implementation to raise an <code>INDEX_SIZE_ERR</code>
   exception.

  <p>The <dfn id=fill title=dom-context-2d-fill><code>fill()</code></dfn>
   method must fill each subpath of the current path in turn, using <code
   title=dom-context-2d-fillStyle><a href="#fillstyle">fillStyle</a></code>,
   and using the non-zero winding number rule. Open subpaths must be
   implicitly closed when being filled (without affecting the actual
   subpaths).

  <p>The <dfn id=stroke
   title=dom-context-2d-stroke><code>stroke()</code></dfn> method must stroke
   each subpath of the current path in turn, using the <code
   title=dom-context-2d-strokeStyle><a
   href="#strokestyle">strokeStyle</a></code>, <code
   title=dom-context-2d-lineWidth><a href="#linewidth">lineWidth</a></code>,
   <code title=dom-context-2d-lineJoin><a
   href="#linejoin">lineJoin</a></code>, and (if appropriate) <code
   title=dom-context-2d-miterLimit><a
   href="#miterlimit">miterLimit</a></code> attributes.

  <p>Paths, when filled or stroked, must be painted without affecting the
   current path, and must be subject to <a
   href="#transformations0">transformations</a>, <a href="#shadows0"
   title=shadows>shadow effects</a>, <a href="#globalalpha"
   title=dom-context-2d-globalAlpha>global alpha</a>, <a href="#clipping"
   title="clipping path">clipping paths</a>, and <a
   href="#globalcompositeoperation"
   title=dom-context-2d-globalCompositeOperation>global composition
   operators</a>.

  <p class=note>The transformation is applied to the path when it is drawn,
   not when the path is constructed. Thus, a single path can be constructed
   and then drawn according to different transformations without recreating
   the path.

  <p>The <dfn id=clip title=dom-context-2d-clip><code>clip()</code></dfn>
   method must create a new <dfn id=clipping>clipping path</dfn> by
   calculating the intersection of the current clipping path and the area
   described by the current path (after applying the <span>current
   transformation</span>), using the non-zero winding number rule. Open
   subpaths must be implicitly closed when computing the clipping path,
   without affecting the actual subpaths.

  <p>When the context is created, the initial clipping path is the rectangle
   with the top left corner at (0,0) and the width and height of the
   coordinate space.</p>
  <!-- XXXv3
   Jordan OSETE suggests:
    * support ways of extending the clip region (union instead of intersection)
       - also "add", "substract", "replace", "intersect" and "xor"
    * support ways of resetting the clip region without save/restore
  -->

  <p>The <dfn id=ispointinpath
   title=dom-context-2d-isPointInPath><code>isPointInPath(<var
   title="">x</var>, <var title="">y</var>)</code></dfn> method must return
   true if the point given by the <var title="">x</var> and <var
   title="">y</var> coordinates passed to the method, when treated as
   coordinates in the canvas' coordinate space unaffected by the current
   transformation, is within the area of the canvas that would be filled if
   the current path was to be filled; and must return false otherwise.

  <h6 id=images><span class=secno>3.14.11.1.9. </span>Images</h6>

  <p>To draw images onto the canvas, the <dfn id=drawimage
   title=dom-context-2d-drawImage><code>drawImage</code></dfn> method can be
   used.

  <p>This method is overloaded with three variants: <code
   title="">drawImage(<var title="">image</var>, <var title="">dx</var>, <var
   title="">dy</var>)</code>, <code title="">drawImage(<var
   title="">image</var>, <var title="">dx</var>, <var title="">dy</var>, <var
   title="">dw</var>, <var title="">dh</var>)</code>, and <code
   title="">drawImage(<var title="">image</var>, <var title="">sx</var>, <var
   title="">sy</var>, <var title="">sw</var>, <var title="">sh</var>, <var
   title="">dx</var>, <var title="">dy</var>, <var title="">dw</var>, <var
   title="">dh</var>)</code>. (Actually it is overloaded with six; each of
   those three can take either an <code><a
   href="#htmlimageelement">HTMLImageElement</a></code> or an <code><a
   href="#htmlcanvaselement">HTMLCanvasElement</a></code> for the <var
   title="">image</var> argument.) If not specified, the <var
   title="">dw</var> and <var title="">dh</var> arguments default to the
   values of <var title="">sw</var> and <var title="">sh</var>, interpreted
   such that one CSS pixel in the image is treated as one unit in the canvas
   coordinate space. If the <var title="">sx</var>, <var title="">sy</var>,
   <var title="">sw</var>, and <var title="">sh</var> arguments are omitted,
   they default to 0, 0, the image's intrinsic width in image pixels, and the
   image's intrinsic height in image pixels, respectively.

  <p>The <var title="">image</var> argument must be an instance of an
   <code><a href="#htmlimageelement">HTMLImageElement</a></code> or <code><a
   href="#htmlcanvaselement">HTMLCanvasElement</a></code>. If the <var
   title="">image</var> is of the wrong type, the implementation must raise a
   <code>TYPE_MISMATCH_ERR</code> exception. If one of the <var
   title="">sy</var>, <var title="">sw</var>, <var title="">sw</var>, and
   <var title="">sh</var> arguments is outside the size of the image, or if
   one of the <var title="">dw</var> and <var title="">dh</var> arguments is
   negative, the implementation must raise an <code>INDEX_SIZE_ERR</code>
   exception. If the <var title="">image</var> argument is an <code><a
   href="#htmlimageelement">HTMLImageElement</a></code> object whose <code
   title=dom-attr-complete>complete</code> attribute is false, then the
   implementation must raise an <code>INVALID_STATE_ERR</code> exception.

  <p>When <code title=dom-context-2d-drawImage><a
   href="#drawimage">drawImage()</a></code> is invoked, the specified region
   of the image specified by the source rectangle (<var title="">sx</var>,
   <var title="">sy</var>, <var title="">sw</var>, <var title="">sh</var>)
   must be painted on the region of the canvas specified by the destination
   rectangle (<var title="">dx</var>, <var title="">dy</var>, <var
   title="">dw</var>, <var title="">dh</var>).

  <p><img alt="" src="images/drawImage.png"></p>
  <!-- no alt="" text
  since the image is just repeating what was stated in the previous
  paragraph. -->

  <p>Images are painted without affecting the current path, and are subject
   to <a href="#transformations0">transformations</a>, <a href="#shadows0"
   title=shadows>shadow effects</a>, <a href="#globalalpha"
   title=dom-context-2d-globalAlpha>global alpha</a>, <a href="#clipping"
   title="clipping path">clipping paths</a>, and <a
   href="#globalcompositeoperation"
   title=dom-context-2d-globalCompositeOperation>global composition
   operators</a>.</p>
  <!-- XXX should somehow say that the image used is the actual image
  of the target element, not the rendered image (e.g. height/width
  attributes don't affect it -->

  <h6 id=pixel><span class=secno>3.14.11.1.10. </span><dfn id=pixel0>Pixel
   manipulation</dfn></h6>

  <p>The <dfn id=getimagedata
   title=dom-context-2d-getImageData><code>getImageData(<var
   title="">sx</var>, <var title="">sy</var>, <var title="">sw</var>, <var
   title="">sh</var>)</code></dfn> method must return an <code><a
   href="#imagedata">ImageData</a></code> object representing the underlying
   pixel data for the area of the canvas denoted by the rectangle which has
   one corner at the (<var title="">sx</var>, <var title="">sy</var>)
   coordinate, and that has width <var title="">sw</var> and height <var
   title="">sh</var>. Pixels outside the canvas must be returned as
   transparent black. Pixels must be returned as non-premultiplied alpha
   values.

  <p><code><a href="#imagedata">ImageData</a></code> objects must be
   initialised so that their <dfn id=height5
   title=dom-imagedata-height><code>height</code></dfn> attribute is set to
   <var title="">h</var>, the number of rows in the image data, their <dfn
   id=width5 title=dom-imagedata-width><code>width</code></dfn> attribute is
   set to <var title="">w</var>, the number of physical device pixels per row
   in the image data, and the <dfn id=data1
   title=dom-imagedata-data><code>data</code></dfn> attribute is initialised
   to an array of <var title="">h</var>&times;<var title="">w</var>&times;4
   integers. The pixels must be represented in this array in left-to-right
   order, row by row, starting at the top left, with each pixel's red, green,
   blue, and alpha components being given in that order. Each component of
   each device pixel represented in this array must be in the range 0..255,
   representing the 8 bit value for that component. At least one pixel must
   be returned.

  <p class=note>The width and height (<var title="">w</var> and <var
   title="">h</var>) might be different than the <var title="">sw</var> and
   <var title="">sh</var> arguments to the function, e.g. if the canvas is
   backed by a high-resolution bitmap.

  <p>If the <code title=dom-context-2d-getImageData><a
   href="#getimagedata">getImageData(<var title="">sx</var>, <var
   title="">sy</var>, <var title="">sw</var>, <var
   title="">sh</var>)</a></code> method is called with either the <var
   title="">sw</var> or <var title="">sh</var> arguments set to zero or
   negative values, the method must raise an <code>INDEX_SIZE_ERR</code>
   exception.

  <p>The <dfn id=putimagedata
   title=dom-context-2d-putImageData><code>putImageData(<var
   title="">image</var>, <var title="">dx</var>, <var
   title="">dy</var>)</code></dfn> method must take the given <code><a
   href="#imagedata">ImageData</a></code> structure, and draw it at the
   specified location <var title="">dx</var>,<var title="">dy</var> in the
   canvas coordinate space, mapping each pixel represented by the <code><a
   href="#imagedata">ImageData</a></code> structure into one device pixel.

  <p>If the first argument to the method is not an object whose [[Class]]
   property is <code><a href="#imagedata">ImageData</a></code>, but all of
   the following conditions are true, then the method must treat the first
   argument as if it was an <code><a href="#imagedata">ImageData</a></code>
   object (and thus not raise the <code>TYPE_MISMATCH_ERR</code> exception):

  <ul>
   <li>The method's first argument is an object with <code
    title=dom-imagedata-width><a href="#width5">width</a></code> and <code
    title=dom-imagedata-height><a href="#height5">height</a></code>
    attributes with integer values and a <code title=dom-imagedata-data><a
    href="#data1">data</a></code> attribute whose value is an integer array.

   <li>The <code><a href="#imagedata">ImageData</a></code> object's <code
    title=dom-imagedata-width><a href="#width5">width</a></code> is greater
    than zero.

   <li>The <code><a href="#imagedata">ImageData</a></code> object's <code
    title=dom-imagedata-height><a href="#height5">height</a></code> is
    greater than zero.

   <li>The <code><a href="#imagedata">ImageData</a></code> object's <code
    title=dom-imagedata-width><a href="#width5">width</a></code> multiplied
    by its <code title=dom-imagedata-height><a
    href="#height5">height</a></code> multiplied by 4 is equal to the number
    of entries in the <code><a href="#imagedata">ImageData</a></code>
    object's <code title=dom-imagedata-data><a href="#data1">data</a></code>
    array.

   <li>The <code><a href="#imagedata">ImageData</a></code> object's <code
    title=dom-imagedata-data><a href="#data1">data</a></code> array only
    contains entries that are in the range 0 to 255 inclusive.
  </ul>

  <p>The handling of pixel rounding when the specified coordinates do not
   exactly map to the device coordinate space is not defined by this
   specification, except that the following must result in no visible changes
   to the rendering:

  <pre>context.putImageData(context.getImageData(x, y, w, h), x, y);</pre>

  <p>...for any value of <var title="">x</var> and <var title="">y</var>. In
   other words, while user agents may round the arguments of the two methods
   so that they map to device pixel boundaries, any rounding performed must
   be performed consistently for both the <code
   title=dom-context-2d-getImageData><a
   href="#getimagedata">getImageData()</a></code> and <code
   title=dom-context-2d-putImageData><a
   href="#putimagedata">putImageData()</a></code> operations.

  <p>The current transformation matrix must not affect the <code
   title=dom-context-2d-getImageData><a
   href="#getimagedata">getImageData()</a></code> and <code
   title=dom-context-2d-putImageData><a
   href="#putimagedata">putImageData()</a></code> methods.

  <div class=example>
   <p>The data returned by <code title=dom-context-2d-getImageData><a
    href="#getimagedata">getImageData()</a></code> is at the resolution of
    the canvas backing store, which is likely to not be one device pixel to
    each CSS pixel if the display used is a high resolution display. Thus,
    while one could create an <code><a href="#imagedata">ImageData</a></code>
    object, one would net necessarily know what resolution the canvas
    expected (how many pixels the canvas wants to paint over one coordinate
    space unit pixel).</p>

   <p>In the following example, the script first obtains the size of the
    canvas backing store, and then generates a few new <code><a
    href="#imagedata">ImageData</a></code> objects which can be used.</p>

   <pre>
  // canvas is a reference to a &lt;canvas> element
  // (note: this example uses JavaScript 1.7 features)
  var context = canvas.getContext('2d');
  var backingStore = context.getImageData(0, 0, canvas.width, canvas.height);
  var actualWidth = backingStore.width;
  var actualHeight = backingStore.height;

  function CreateImageData(w, h) {
    return {
      height: h,
      width: w,
      data: [i for (i in function (n) { for (let i = 0; i < n; i += 1) yield 0 }(w*h*4)) ]
    };
  }

  // create some plasma
  var plasma = CreateImageData(actualWidth, actualHeight);
  FillPlasma(plasma, 'green'); // green plasma

  // create a cloud
  var could = CreateImageData(actualWidth, actualHeight);
  FillCloud(cloud, actualWidth/2, actualHeight/2); // put a cloud in the middle

  // paint them on top of each other
  context.putImageData(plasma, 0, 0);
  context.putImageData(cloud, 0, 0);

  function FillPlasma(data) { ... }
  function FillCload(data, x, y) { ... }
</pre>
  </div>

  <h6 id=drawing><span class=secno>3.14.11.1.11. </span>Drawing model</h6>

  <p>When a shape or image is painted, user agents must follow these steps,
   in the order given (or act as if they do):

  <ol>
   <li>If the current transformation matrix is infinite, then do nothing.
    Abort these steps.

   <li>The coordinates are transformed by the current transformation matrix.

   <li>The shape or image is rendered, creating image <var title="">A</var>,
    as described in the previous sections. For shapes, the current fill,
    stroke, and line styles must be honoured.

   <li>The shadow is rendered from image <var title="">A</var>, using the
    current shadow styles, creating image <var title="">B</var>.

   <li>Image <var title="">A</var> is composited over image <var
    title="">B</var> creating the source image.

   <li>The source image has its alpha adjusted by <code
    title=dom-context-2d-globalAlpha><a
    href="#globalalpha">globalAlpha</a></code>.

   <li>Within the clip region (as affected by the current transformation
    matrix), the source image is composited over the current canvas bitmap
    using the current composition operator.
  </ol>
  <!--
  <h5 id="3d">The 3D context</h5>

  <p class="big-issue">Well, one day.</p>
-->

  <h4 id=the-map><span class=secno>3.14.12. </span>The <dfn
   id=map><code>map</code></dfn> element</h4>

  <p><a href="#block-level0" title="block-level elements">Block-level
   element</a>.

  <dl class=element>
   <dt>Contexts in which this element may be used:

   <dd>Where <a href="#block-level0">block-level elements</a> are expected.

   <dt>Content model:

   <dd>Zero or more <a href="#block-level0">block-level elements</a>.

   <dt>Element-specific attributes:

   <dd>None.

   <dt>DOM interface:

   <dd>
    <pre
     class=idl>interface <dfn id=htmlmapelement>HTMLMapElement</dfn> : <a href="#htmlelement">HTMLElement</a> {
  readonly attribute <a href="#htmlcollection0">HTMLCollection</a> <a href="#areas" title=dom-map-areas>areas</a>;
};</pre>
  </dl>

  <p>The <code><a href="#map">map</a></code> element, in conjuction with any
   <code><a href="#area">area</a></code> element descendants, defines an <a
   href="#image">image map</a>.

  <p>The <dfn id=areas title=dom-map-areas><code>areas</code></dfn> attribute
   must return an <code><a href="#htmlcollection0">HTMLCollection</a></code>
   rooted at the <code><a href="#map">map</a></code> element, whose filter
   matches only <code><a href="#area">area</a></code> elements.

  <h4 id=the-area><span class=secno>3.14.13. </span>The <dfn
   id=area><code>area</code></dfn> element</h4>

  <p><a href="#strictly">Strictly inline-level content</a>.</p>
  <!-- XXX as defined, the area element on its own isn't enough to
  satisfy "significant inline-level content" model. should it be? -->

  <dl class=element>
   <dt>Contexts in which this element may be used:

   <dd>Where <a href="#strictly">strictly inline-level content</a> is
    allowed, but only as a descendant of a <code><a
    href="#map">map</a></code> element.

   <dt>Content model:

   <dd>Empty.

   <dt>Element-specific attributes:

   <dd><code title=attr-area-alt><a href="#alt1">alt</a></code>

   <dd><code title=attr-area-coords><a href="#coords">coords</a></code>

   <dd><code title=attr-area-shape><a href="#shape">shape</a></code>

   <dd><code title=attr-hyperlink-href><a href="#href6">href</a></code>

   <dd><code title=attr-hyperlink-target><a href="#target3">target</a></code>

   <dd><code title=attr-hyperlink-ping><a href="#ping">ping</a></code>

   <dd><code title=attr-hyperlink-rel><a href="#rel3">rel</a></code>

   <dd><code title=attr-hyperlink-media><a href="#media12">media</a></code>

   <dd><code title=attr-hyperlink-hreflang><a
    href="#hreflang3">hreflang</a></code>

   <dd><code title=attr-hyperlink-type><a href="#type17">type</a></code>

   <dt>DOM interface:

   <dd>
    <pre
     class=idl>interface <dfn id=htmlareaelement>HTMLAreaElement</dfn> : <a href="#htmlelement">HTMLElement</a> {
           attribute DOMString <a href="#alt2" title=dom-area-alt>alt</a>;
           attribute DOMString <a href="#coords0" title=dom-area-coords>coords</a>;
           attribute DOMString <a href="#shape0" title=dom-area-shape>shape</a>;
           attribute DOMString <a href="#href4" title=dom-area-href>href</a>;
           attribute DOMString <a href="#target2" title=dom-area-target>target</a>;
           attribute DOMString <a href="#ping1" title=dom-area-ping>ping</a>;
           attribute DOMString <a href="#rel2" title=dom-area-rel>rel</a>;
  readonly attribute DOMTokenList <a href="#rellist1" title=dom-area-relList>relList</a>;
           attribute DOMString <a href="#media11" title=dom-area-media>media</a>;
           attribute DOMString <a href="#hreflang2" title=dom-area-hreflang>hreflang</a>;
           attribute DOMString <a href="#type10" title=dom-area-type>type</a>;
};</pre>
  </dl>

  <p>The <code><a href="#area">area</a></code> element represents either a
   hyperlink with some text and a corresponding area on an <a
   href="#image">image map</a>, or a dead area on an image map.

  <p>If the <code><a href="#area">area</a></code> element has an <code
   title=attr-hyperlink-href><a href="#href6">href</a></code> attribute, then
   the <code><a href="#area">area</a></code> element represents a <a
   href="#hyperlinks">hyperlink</a>; the <dfn id=alt1
   title=attr-area-alt><code>alt</code></dfn> attribute, which must then be
   present, specifies the text.

  <p>However, if the <code><a href="#area">area</a></code> element has no
   <code title=attr-hyperlink-href><a href="#href6">href</a></code>
   attribute, then the area represented by the element cannot be selected,
   and the <code title=attr-area-alt><a href="#alt1">alt</a></code> attribute
   must be omitted.

  <p>In both cases, the <code title=attr-area-shape><a
   href="#shape">shape</a></code> and <code title=attr-area-coords><a
   href="#coords">coords</a></code> attributes specify the area.

  <p>The <dfn id=shape title=attr-area-shape><code>shape</code></dfn>
   attribute is an <a href="#enumerated">enumerated attribute</a>. The
   following table lists the keywords defined for this attribute. The states
   given in the first cell of the the rows with keywords give the states to
   which those keywords map. Some of the keywords are non-conforming, as
   noted in the last column.

  <table>
   <thead>
    <tr>
     <th>State

     <th>Keywords

     <th>Notes

   <tbody>
    <tr>
     <td rowspan=2><dfn id=circle title=attr-area-shape-circle>Circle
      state</dfn>

     <td><code title="">circ</code>

     <td>Non-conforming

    <tr>
     <td><code title="">circle</code>

     <td>

    <tr>
     <td><dfn id=default0 title=attr-area-shape-default>Default state</dfn>

     <td><code title="">default</code>

     <td>

    <tr>
     <td rowspan=2><dfn id=polygon title=attr-area-shape-poly>Polygon
      state</dfn>

     <td><code title="">poly</code>

     <td>

    <tr>
     <td><code title="">polygon</code>

     <td>Non-conforming

    <tr>
     <td rowspan=2><dfn id=rectangle title=attr-area-shape-rect>Rectangle
      state</dfn>

     <td><code title="">rect</code>

     <td>

    <tr>
     <td><code title="">rectangle</code>

     <td>Non-conforming
  </table>

  <p>The attribute may be ommited. The <i>missing value default</i> is the <a
   href="#rectangle" title=attr-area-shape-rect>rectangle</a> state.

  <p>The <dfn id=coords title=attr-area-coords><code>coords</code></dfn>
   attribute must, if specified, contain a <a href="#valid4">valid list of
   integers</a>. This attribute gives the coordinates for the shape described
   by the <code title=attr-area-shape><a href="#shape">shape</a></code>
   attribute. The processing for this attribute is described as part of the
   <a href="#image">image map</a> processing model.

  <p>In the <a href="#circle" title=attr-area-shape-circle>circle state</a>,
   <code><a href="#area">area</a></code> elements must have a <code
   title=attr-area-coords><a href="#coords">coords</a></code> attribute
   present, with three integers, the last of which must be non-negative. The
   first integer must be the distance in CSS pixels from the left edge of the
   image to the center of the circle, the second integer must be the distance
   in CSS pixels from the top edge of the image to the center of the circle,
   and the third integer must be the radius of the circle, again in CSS
   pixels.

  <p>In the <a href="#default0" title=attr-area-shape-default>default
   state</a> state, <code><a href="#area">area</a></code> elements must not
   have a <code title=attr-area-coords><a href="#coords">coords</a></code>
   attribute.

  <p>In the <a href="#polygon" title=attr-area-shape-poly>polygon state</a>,
   <code><a href="#area">area</a></code> elements must have a <code
   title=attr-area-coords><a href="#coords">coords</a></code> attribute with
   at least six integers, and the number of integers must be even. Each pair
   of integers must represent a coordinate given as the distances from the
   left and the top of the image in CSS pixels respectively, and all the
   coordinates together must represent the points of the polygon, in order.

  <p>In the <a href="#rectangle" title=attr-area-shape-rect>rectangle
   state</a>, <code><a href="#area">area</a></code> elements must have a
   <code title=attr-area-coords><a href="#coords">coords</a></code> attribute
   with exactly four integers, the first of which must be less than the
   third, and the second of which must be less than the fourth. The four
   points must represent, respectively, the distance from the left edge of
   the image to the top left side of the rectangle, the distance from the top
   edge to the top side, the distance from the left edge to the right side,
   and the distance from the top edge to the bottom side, all in CSS pixels.

  <p>When user agents allow users to <a href="#following0" title="following
   hyperlinks">follow hyperlinks</a> created using the <code><a
   href="#area">area</a></code> element, as described in the next section,
   the <code title=attr-hyperlink-href><a href="#href6">href</a></code>,
   <code title=attr-hyperlink-target><a href="#target3">target</a></code> and
   <code title=attr-hyperlink-ping><a href="#ping">ping</a></code> attributes
   decide how the link is followed. The <code title=attr-hyperlink-rel><a
   href="#rel3">rel</a></code>, <code title=attr-hyperlink-media><a
   href="#media12">media</a></code>, <code title=attr-hyperlink-hreflang><a
   href="#hreflang3">hreflang</a></code>, and <code
   title=attr-hyperlink-type><a href="#type17">type</a></code> attributes may
   be used to indicate to the user the likely nature of the target resource
   before the user follows the link.

  <p>The <code title=attr-hyperlink-target><a
   href="#target3">target</a></code>, <code title=attr-hyperlink-ping><a
   href="#ping">ping</a></code>, <code title=attr-hyperlink-rel><a
   href="#rel3">rel</a></code>, <code title=attr-hyperlink-media><a
   href="#media12">media</a></code>, <code title=attr-hyperlink-hreflang><a
   href="#hreflang3">hreflang</a></code>, and <code
   title=attr-hyperlink-type><a href="#type17">type</a></code> attributes
   must be omitted if the <code title=attr-hyperlink-href><a
   href="#href6">href</a></code> attribute is not present.

  <p>The <a href="#activation0">activation behavior</a> of <code><a
   href="#area">area</a></code> elements is to run the following steps:

  <ol>
   <li>If the <code title=event-DOMActivate>DOMActivate</code> event in
    question is not <span title=concept-events-trusted>trusted</span> (i.e. a
    <code title=dom-click><a href="#click">click()</a></code> method call was
    the reason for the event being dispatched), and the <code><a
    href="#area">area</a></code> element's <code
    title=attr-area-target>target</code> attribute is <span
    class=big-issue>...</span> then raise an <code>INVALID_ACCESS_ERR</code>
    exception.

   <li>Otherwise, the user agent must <a href="#following0" title="following
    hyperlinks">follow the hyperlink</a> defined by the <code><a
    href="#area">area</a></code> element, if any.
  </ol>

  <p class=note>One way that a user agent can enable users to follow
   hyperlinks is by allowing <code><a href="#area">area</a></code> elements
   to be clicked, or focussed and activated by the keyboard. This <a
   href="#interactive1" title="interactive elements">will cause</a> the
   aforementioned <a href="#activation0">activation behavior</a> to be
   invoked.

  <p>The DOM attributes <dfn id=alt2
   title=dom-area-alt><code>alt</code></dfn>, <dfn id=coords0
   title=dom-area-coords><code>coords</code></dfn>, <dfn id=shape0
   title=dom-area-shape><code>shape</code></dfn>, <dfn id=href4
   title=dom-area-href><code>href</code></dfn>, <dfn id=target2
   title=dom-area-target><code>target</code></dfn>, <dfn id=ping1
   title=dom-area-ping><code>ping</code></dfn>, <dfn id=rel2
   title=dom-area-rel><code>rel</code></dfn>, <dfn id=media11
   title=dom-area-media><code>media</code></dfn>, <dfn id=hreflang2
   title=dom-area-hreflang><code>hreflang</code></dfn>, and <dfn id=type10
   title=dom-area-type><code>type</code></dfn>, each must <a
   href="#reflect">reflect</a> the respective content attributes of the same
   name.

  <p>The DOM attribute <dfn id=rellist1
   title=dom-area-rellist><code>relList</code></dfn> must <a
   href="#reflect">reflect</a> the <code title=attr-hyperlink-rel><a
   href="#rel3">rel</a></code> content attribute.

  <h4 id=image-maps><span class=secno>3.14.14. </span>Image maps</h4>
  <!-- TESTS
  http://software.hixie.ch/utilities/js/live-dom-viewer/?%3C%21DOCTYPE%20html%3E%0A%3Cimg%20src%3D%22http%3A//hixie.ch/resources/images/smallcats%22%20usemap%3D%23a%20onclick%3Dw%28%27img%27%29%3E%0A%3Cmap%20name%3Da%3E%0A%20%3Carea%20onclick%3Dw%28%271%27%29%20coords%3D%270%25%200%25%20100%25%20100%25%27%20href%3Djavascript%3A%3E%0A%3C/map%3E
  http://software.hixie.ch/utilities/js/live-dom-viewer/?%3C%21DOCTYPE%20html%3E%0A%3Cbody%20onfocus%3D%22w%28document.activeElement.tagName%29%22%3E%0A%3Cimg%20src%3D%22http%3A//hixie.ch/resources/images/smallcats%22%20usemap%3D%23a%20onclick%3Dw%28%27img%27%29%20onfocus%3D%22w%28document.activeElement.tagName%29%22%3E%0A%3Cimg%20src%3D%22http%3A//hixie.ch/resources/images/sample%22%20usemap%3D%23a%20onclick%3Dw%28%27img%27%29%20onfocus%3D%22w%28document.activeElement.tagName%29%22%3E%0A%3Cmap%20name%3Da%20onfocus%3D%22w%28document.activeElement.tagName%29%22%3E%0A%20%3Carea%20onclick%3Dw%28%271%27%29%20coords%3D%270%200%2050%2050%27%20href%3Djavascript%3A%20onfocus%3D%22w%28document.activeElement.tagName%29%22%3E%0A%3C/map%3E%0A%3Cscript%3E%0A%20var%20x%20%3D%20document.getElementsByTagName%28%27img%27%29%5B0%5D%3B%0A%20x.parentNode.appendChild%28x%29%3B%0A%20document.getElementsByTagName%28%27area%27%29%5B0%5D.focus%28%29%3B%0A%3C/script%3E
  http://software.hixie.ch/utilities/js/live-dom-viewer/?%3C%21DOCTYPE%20html%3Ex%3Cmap%3E%3Carea%20shape%3Dpolyg%20coords%3D%221%2C2%203%22%3E%3C/map%3E%0A%3Cscript%3Ex%20%3D%20document.getElementsByTagName%28%27area%27%29%5B0%5D%3B%20w%28x.shape%20+%20%27%20%27%20+%20x.coords%29%3C/script%3E
  http://software.hixie.ch/utilities/js/live-dom-viewer/?%3C%21DOCTYPE%20html%3E%0D%0A%3Cp%3E%3Cimg%20src%3D%22http%3A//hixie.ch/resources/images/astrophy/128%22%20usemap%3D%23a%3E%0D%0A%3Cmap%20name%3Da%3E%3Carea%20shape%3Dcirc%20coords%3D%2220%2C20%2C10%25%22%20href%3D%23%3E%3Carea%20shape%3Dcirc%20coords%3D%2220%2C20%2C10%22%20href%3D%23%3E%3C/map%3E%0D%0A%3Cscript%3Edocument.write%28document.getElementsByTagName%28%27area%27%29%5B0%5D.coords%29%3C/script%3E
  -->

  <p>An <dfn id=image>image map</dfn> allows geometric areas on an image to
   be associated with <a href="#hyperlinks" title=hyperlink>hyperlinks</a>.

  <p>An image, in the form of an <code><a href="#img">img</a></code> element
   or an <code><a href="#object">object</a></code> element representing an
   image, may be associated with an image map (in the form of a <code><a
   href="#map">map</a></code> element) by specifying a <dfn id=usemap1
   title=attr-hyperlink-usemap><code>usemap</code></dfn> attribute on the
   <code><a href="#img">img</a></code> or <code><a
   href="#object">object</a></code> element. The <code
   title=attr-area-usemap>usemap</code> attribute, if specified, must be a <a
   href="#valid7">valid hashed ID reference</a> to a <code><a
   href="#map">map</a></code> element.

  <p>If an <code><a href="#img">img</a></code> element or an <code><a
   href="#object">object</a></code> element representing an image has a <code
   title=attr-area-usemap>usemap</code> attribute specified, user agents must
   process it as follows:

  <ol>
   <li>
    <p>First, <a href="#rules5">rules for parsing a hashed ID reference</a>
     to a <code><a href="#map">map</a></code> element must be followed. This
     will return either an element (the <var title="">map</var>) or null.

   <li>
    <p>If that returned null, then abort these steps. The image is not
     associated with an image map after all.

   <li>
    <p>Otherwise, the user agent must collect all the <code><a
     href="#area">area</a></code> elements that are descendants of the <var
     title="">map</var>. Let those be the <var title="">areas</var>.
  </ol>

  <p>Having obtained the list of <code><a href="#area">area</a></code>
   elements that form the image map (the <var title="">areas</var>),
   interactive user agents must process the list in one of two ways.

  <p>If the user agent intends to show the text that the <code><a
   href="#img">img</a></code> element represents, then it must use the
   following steps.

  <p class=note>In user agents that do not support images, or that have
   images disabled, <code><a href="#object">object</a></code> elements cannot
   represent images, and thus this section never applies (the fallback
   content is shown instead). The following steps therefore only apply to
   <code><a href="#img">img</a></code> elements.

  <ol>
   <li>
    <p>Remove all the <code><a href="#area">area</a></code> elements in <var
     title="">areas</var> that have no <code title=attr-hyperlink-href><a
     href="#href6">href</a></code> attribute.

   <li>
    <p>Remove all the <code><a href="#area">area</a></code> elements in <var
     title="">areas</var> that have no <code title=attr-area-alt><a
     href="#alt1">alt</a></code> attribute, or whose <code
     title=attr-area-alt><a href="#alt1">alt</a></code> attribute's value is
     the empty string, <em>if</em> there is another <code><a
     href="#area">area</a></code> element in <var title="">areas</var> with
     the same value in the <code title=attr-hyperlink-href><a
     href="#href6">href</a></code> attribute and with a non-empty <code
     title=attr-area-alt><a href="#alt1">alt</a></code> attribute.

   <li>
    <p>Each remaining <code><a href="#area">area</a></code> element in <var
     title="">areas</var> represents a <a href="#hyperlinks">hyperlink</a>.
     Those hyperlinks should all be made available to the user in a manner
     associated with the text of the <code><a href="#img">img</a></code>
     element.</p>

    <p>In this context, user agents may represent <code><a
     href="#area">area</a></code> and <code><a href="#img">img</a></code>
     elements with no specified <code title="">alt</code> attributes, or
     whose <code title="">alt</code> attributes are the empty string or some
     other non-visible text, in a user-agent-defined fashion intended to
     indicate the lack of suitable author-provided text.
  </ol>

  <p>If the user agent intends to show the image and allow interaction with
   the image to select hyperlinks, then the image must be associated with a
   set of layered shapes, taken from the <code><a
   href="#area">area</a></code> elements in <var title="">areas</var>, in
   reverse tree order (so the last specified <code><a
   href="#area">area</a></code> element in the <var title="">map</var> is the
   bottom-most shape, and the first element in the <var title="">map</var>,
   in tree order, is the top-most shape).

  <p>Each <code><a href="#area">area</a></code> element in <var
   title="">areas</var> must be processed as follows to obtain a shape to
   layer onto the image:

  <ol>
   <li>
    <p>Find the state that the element's <code title=attr-area-shape><a
     href="#shape">shape</a></code> attribute represents.

   <li>
    <p>Use the <a href="#rules3">rules for parsing a list of integers</a> to
     parse the element's <code title=attr-area-coords><a
     href="#coords">coords</a></code> attribute, if it is present, and let
     the result be the <var title="">coords</var> list. If the attribute is
     absent, let the <var title="">coords</var> list be the empty list.

   <li>
    <p>If the number of items in the <var title="">coords</var> list is less
     than the minimum number given for the <code><a
     href="#area">area</a></code> element's current state, as per the
     following table, then the shape is empty; abort these steps.</p>

    <table>
     <thead>
      <tr>
       <th>State

       <th>Minimum number of items

     <tbody>
      <tr>
       <td><a href="#circle" title=attr-area-shape-circle>Circle state</a>

       <td>3

      <tr>
       <td><a href="#default0" title=attr-area-shape-default>Default
        state</a>

       <td>0

      <tr>
       <td><a href="#polygon" title=attr-area-shape-poly>Polygon state</a>

       <td>6

      <tr>
       <td><a href="#rectangle" title=attr-area-shape-rect>Rectangle
        state</a>

       <td>4
    </table>

   <li>
    <p>Check for excess items in the <var title="">coords</var> list as per
     the entry in the following list corresponding to the <code
     title=attr-area-shape><a href="#shape">shape</a></code> attribute's
     state:</p>

    <dl class=switch>
     <dt><a href="#circle" title=attr-area-shape-circle>Circle state</a>

     <dd>Drop any items in the list beyond the third.

     <dt><a href="#default0" title=attr-area-shape-default>Default state</a>

     <dd>Drop all items in the list.

     <dt><a href="#polygon" title=attr-area-shape-poly>Polygon state</a>

     <dd>Drop the last item if there's an odd number of items.

     <dt><a href="#rectangle" title=attr-area-shape-rect>Rectangle state</a>

     <dd>Drop any items in the list beyond the fourth.
    </dl>

   <li>
    <p>If the <code title=attr-area-shape><a href="#shape">shape</a></code>
     attribute represents the <a href="#rectangle"
     title=attr-area-shape-rect>rectangle state</a>, and the first number in
     the list is numerically less than the third number in the list, then
     swap those two numbers around.

   <li>
    <p>If the <code title=attr-area-shape><a href="#shape">shape</a></code>
     attribute represents the <a href="#rectangle"
     title=attr-area-shape-rect>rectangle state</a>, and the second number in
     the list is numerically less than the fourth number in the list, then
     swap those two numbers around.

   <li>
    <p>If the <code title=attr-area-shape><a href="#shape">shape</a></code>
     attribute represents the <a href="#circle"
     title=attr-area-shape-circle>circle state</a>, and the third number in
     the list is less than or equal to zero, then the shape is empty; abort
     these steps.

   <li>
    <p>Now, the shape represented by the element is the one described for the
     entry in the list below corresponding to the state of the <code
     title=attr-area-shape><a href="#shape">shape</a></code> attribute:</p>

    <dl class=switch>
     <dt><a href="#circle" title=attr-area-shape-circle>Circle state</a>

     <dd>
      <p>Let <var title="">x</var> be the first number in <var
       title="">coords</var>, <var title="">y</var> be the second number, and
       <var title="">r</var> be the third number.</p>

      <p>The shape is a circle whose center is <var title="">x</var> CSS
       pixels from the left edge of the image and <var title="">x</var> CSS
       pixels from the top edge of the image, and whose radius is <var
       title="">r</var> pixels.</p>

     <dt><a href="#default0" title=attr-area-shape-default>Default state</a>

     <dd>
      <p>The shape is a rectangle that exactly covers the entire image.</p>

     <dt><a href="#polygon" title=attr-area-shape-poly>Polygon state</a>

     <dd>
      <p>Let <var title="">x<sub title=""><var title="">i</var></sub></var>
       be the <span>(2<var title="">i</var>)</span>th entry in <var
       title="">coords</var>, and <var title="">y<sub title=""><var
       title="">i</var></sub></var> be the <span>(2<var
       title="">i</var>+1)</span>th entry in <var title="">coords</var> (the
       first entry in <var title="">coords</var> being the one with index 0).</p>

      <p>Let <var title="">the coordinates</var> be (<var title="">x<sub
       title=""><var title="">i</var></sub></var>, <var title="">y<sub
       title=""><var title="">i</var></sub></var>), interpreted in CSS pixels
       measured from the top left of the image, for all integer values of
       <var title="">i</var> from 0 to <span>(<var
       title="">N</var>/2)-1</span>, where <var title="">N</var> is the
       number of items in <var title="">coords</var>.</p>

      <p>The shape is a polygon whose vertices are given by <var title="">the
       coordinates</var>, and whose interior is established using the
       even-odd rule. <a href="#refsGRAPHICS">[GRAPHICS]</a></p>
      <!-- If anyone has this book ("Computer Graphics: Principles and
           Practice in C"), please check page 34 or so and see if it
           makes any references to literature in the bibliographic
           section to define the "even-odd" rule for polygon filling
           and hit testing.
        <dd id="refsGRAPHICS">[GRAPHICS]</dd>
        <dd>(Non-normative) <cite>Computer Graphics: Principles and Practice in C</cite>, Second Edition, J. Foley, A. van Dam, S. Feiner, J. Hughes. Addison-Wesley, July 1995. ISBN 0-201-84840-6.</dd>
      -->
      <!--
        browsers implement the even-odd rule / even winding rule:
        http://software.hixie.ch/utilities/js/live-dom-viewer/?%3C%21DOCTYPE%20html%3E%0A%3Cimg%20usemap%3D%22%23x%22%20src%3D%22/resources/images/sample%22%3E%0A%3Cmap%20name%3D%22x%22%3E%0A%20%20%3Carea%20shape%3Dpolygon%20coords%3D%220%2C0%200%2C100%20100%2C100%20100%2C2%201%2C2%202%2C1%202%2C99%2099%2C99%2099%2C0%22%20href%3Da%3E%0A%3C/map%3E%0A
       -->
      

     <dt><a href="#rectangle" title=attr-area-shape-rect>Rectangle state</a>

     <dd>
      <p>Let <var title="">x1</var> be the first number in <var
       title="">coords</var>, <var title="">y1</var> be the second number,
       <var title="">x2</var> be the third number, and <var title="">y2</var>
       be the fourth number.</p>

      <p>The shape is a rectangle whose top-left corner is given by the
       coordinate (<var title="">x1</var>, <var title="">y1</var>) and whose
       bottom right corner is given by the coordinate (<var
       title="">x2</var>, <var title="">y2</var>), those coordinates being
       interpreted as CSS pixels from the top left corner of the image.</p>
    </dl>
  </ol>

  <p>Mouse clicks on an image associated with a set of layered shapes per the
   above algorithm must be dispatched to the top-most shape covering the
   point that the pointing device indicated (if any), and then, must be
   dispatched again (with a new <code>Event</code> object) to the image
   element itself. User agents may also allow individual <code><a
   href="#area">area</a></code> elements representing <a href="#hyperlinks"
   title=hyperlink>hyperlinks</a> to be selected and activated (e.g. using a
   keyboard); events from this are not also propagated to the image.

  <p class=note>Because a <code><a href="#map">map</a></code> element (and
   its <code><a href="#area">area</a></code> elements) can be associated with
   multiple <code><a href="#img">img</a></code> elements, it is possible for
   an <code><a href="#area">area</a></code> element to correspond to multiple
   focusable areas of the document.

  <p>Image maps are <em><a href="#live">live</a></em>; if the DOM is mutated,
   then the user agent must act as if it had rerun the algorithms for image
   maps.

  <h3 id=tabular><span class=secno>3.15. </span>Tabular data</h3>

  <h4 id=the-table><span class=secno>3.15.1. </span>The <dfn
   id=table><code>table</code></dfn> element</h4>

  <p><a href="#block-level0" title="block-level elements">Block-level
   element</a>, and <a href="#structured" title="structured inline-level
   elements">structured inline-level element</a>.

  <dl class=element>
   <dt>Contexts in which this element may be used:

   <dd>Where <a href="#block-level0">block-level elements</a> are expected.

   <dd>Where <a href="#structured">structured inline-level elements</a> are
    allowed.

   <dt>Content model:

   <dd>In this order: optionally a <code><a
    href="#caption0">caption</a></code> element, followed by either zero or
    more <code><a href="#colgroup">colgroup</a></code> elements, followed
    optionally by a <code><a href="#thead0">thead</a></code> element,
    followed optionally by a <code><a href="#tfoot0">tfoot</a></code>
    element, followed by either zero or more <code><a
    href="#tbody">tbody</a></code> elements <em>or</em> one or more <code><a
    href="#tr">tr</a></code> elements, followed optionally by a <code><a
    href="#tfoot0">tfoot</a></code> element (but there can only be one
    <code><a href="#tfoot0">tfoot</a></code> element child in total).

   <dt>Element-specific attributes:

   <dd>None.

   <dt>DOM interface:

   <dd>
    <pre
     class=idl>interface <dfn id=htmltableelement>HTMLTableElement</dfn> : <a href="#htmlelement">HTMLElement</a> {
           attribute <span>HTMLTableCaptionElement</span> <a href="#caption" title=dom-table-caption>caption</a>;
  HTMLElement <a href="#createcaption" title=dom-table-createCaption>createCaption</a>();
  void <a href="#deletecaption" title=dom-table-deleteCaption>deleteCaption</a>();
           attribute <a href="#htmltablesectionelement">HTMLTableSectionElement</a> <a href="#thead" title=dom-table-tHead>tHead</a>;
  HTMLElement <a href="#createthead" title=dom-table-createTHead>createTHead</a>();
  void <a href="#deletethead" title=dom-table-deleteTHead>deleteTHead</a>();
           attribute <a href="#htmltablesectionelement">HTMLTableSectionElement</a> <a href="#tfoot" title=dom-table-tFoot>tFoot</a>;
  HTMLElement <a href="#createtfoot" title=dom-table-createTFoot>createTFoot</a>();
  void <a href="#deletetfoot" title=dom-table-deleteTFoot>deleteTFoot</a>();
  readonly attribute <a href="#htmlcollection0">HTMLCollection</a> <a href="#tbodies" title=dom-table-tBodies>tBodies</a>;
  readonly attribute <a href="#htmlcollection0">HTMLCollection</a> <a href="#rows" title=dom-table-rows>rows</a>;
  HTMLElement <a href="#insertrow" title=dom-table-insertRow>insertRow</a>(in long index);
  void <a href="#deleterow" title=dom-table-deleteRow>deleteRow</a>(in long index);
};</pre>
  </dl>

  <p>The <code><a href="#table">table</a></code> element represents data with
   more than one dimension (a <a href="#table1"
   title=concept-table>table</a>).

  <p>The children of a <code><a href="#table">table</a></code> element must
   be, in order:

  <ol>
   <li>
    <p>Zero or one <code><a href="#caption0">caption</a></code> elements.

   <li>
    <p>Zero or more <code><a href="#colgroup">colgroup</a></code> elements.

   <li>
    <p>Zero or one <code><a href="#thead0">thead</a></code> elements.

   <li>
    <p>Zero or one <code><a href="#tfoot0">tfoot</a></code> elements, if the
     last element in the table is not a <code><a
     href="#tfoot0">tfoot</a></code> element.

   <li>
    <p>Either:</p>

    <ul>
     <li>Zero or more <code><a href="#tbody">tbody</a></code> elements, or

     <li>One or more <code><a href="#tr">tr</a></code> elements.
    </ul>

   <li>
    <p>Zero or one <code><a href="#tfoot0">tfoot</a></code> element, if there
     are no other <code><a href="#tfoot0">tfoot</a></code> elements in the
     table.
  </ol>

  <p>The <code><a href="#table">table</a></code> element takes part in the <a
   href="#table0">table model</a>.

  <p>The <dfn id=caption title=dom-table-caption><code>caption</code></dfn>
   DOM attribute must return, on getting, the first <code><a
   href="#caption0">caption</a></code> element child of the <code><a
   href="#table">table</a></code> element. On setting, if the new value is a
   <code><a href="#caption0">caption</a></code> element, the first <code><a
   href="#caption0">caption</a></code> element child of the <code><a
   href="#table">table</a></code> element, if any, must be removed, and the
   new value must be inserted as the first node of the <code><a
   href="#table">table</a></code> element. If the new value is not a <code><a
   href="#caption0">caption</a></code> element, then a
   <code>HIERARCHY_REQUEST_ERR</code> DOM exception must be raised instead.

  <p>The <dfn id=createcaption
   title=dom-table-createCaption><code>createCaption()</code></dfn> method
   must return the first <code><a href="#caption0">caption</a></code> element
   child of the <code><a href="#table">table</a></code> element, if any;
   otherwise a new <code><a href="#caption0">caption</a></code> element must
   be created, inserted as the first node of the <code><a
   href="#table">table</a></code> element, and then returned.

  <p>The <dfn id=deletecaption
   title=dom-table-deleteCaption><code>deleteCaption()</code></dfn> method
   must remove the first <code><a href="#caption0">caption</a></code> element
   child of the <code><a href="#table">table</a></code> element, if any.

  <p>The <dfn id=thead title=dom-table-tHead><code>tHead</code></dfn> DOM
   attribute must return, on getting, the first <code><a
   href="#thead0">thead</a></code> element child of the <code><a
   href="#table">table</a></code> element. On setting, if the new value is a
   <code><a href="#thead0">thead</a></code> element, the first <code><a
   href="#thead0">thead</a></code> element child of the <code><a
   href="#table">table</a></code> element, if any, must be removed, and the
   new value must be inserted immediately before the first element in the
   <code><a href="#table">table</a></code> element that is neither a <code><a
   href="#caption0">caption</a></code> element nor a <code><a
   href="#colgroup">colgroup</a></code> element, if any, or at the end of the
   table otherwise. If the new value is not a <code><a
   href="#thead0">thead</a></code> element, then a
   <code>HIERARCHY_REQUEST_ERR</code> DOM exception must be raised instead.

  <p>The <dfn id=createthead
   title=dom-table-createTHead><code>createTHead()</code></dfn> method must
   return the first <code><a href="#thead0">thead</a></code> element child of
   the <code><a href="#table">table</a></code> element, if any; otherwise a
   new <code><a href="#thead0">thead</a></code> element must be created and
   inserted immediately before the first element in the <code><a
   href="#table">table</a></code> element that is neither a <code><a
   href="#caption0">caption</a></code> element nor a <code><a
   href="#colgroup">colgroup</a></code> element, if any, or at the end of the
   table otherwise, and then that new element must be returned.

  <p>The <dfn id=deletethead
   title=dom-table-deleteTHead><code>deleteTHead()</code></dfn> method must
   remove the first <code><a href="#thead0">thead</a></code> element child of
   the <code><a href="#table">table</a></code> element, if any.

  <p>The <dfn id=tfoot title=dom-table-tFoot><code>tFoot</code></dfn> DOM
   attribute must return, on getting, the first <code><a
   href="#tfoot0">tfoot</a></code> element child of the <code><a
   href="#table">table</a></code> element. On setting, if the new value is a
   <code><a href="#tfoot0">tfoot</a></code> element, the first <code><a
   href="#tfoot0">tfoot</a></code> element child of the <code><a
   href="#table">table</a></code> element, if any, must be removed, and the
   new value must be inserted immediately before the first element in the
   <code><a href="#table">table</a></code> element that is neither a <code><a
   href="#caption0">caption</a></code> element, a <code><a
   href="#colgroup">colgroup</a></code> element, nor a <code><a
   href="#thead0">thead</a></code> element, if any, or at the end of the
   table if there are no such elements. If the new value is not a <code><a
   href="#tfoot0">tfoot</a></code> element, then a
   <code>HIERARCHY_REQUEST_ERR</code> DOM exception must be raised instead.

  <p>The <dfn id=createtfoot
   title=dom-table-createTFoot><code>createTFoot()</code></dfn> method must
   return the first <code><a href="#tfoot0">tfoot</a></code> element child of
   the <code><a href="#table">table</a></code> element, if any; otherwise a
   new <code><a href="#tfoot0">tfoot</a></code> element must be created and
   inserted immediately before the first element in the <code><a
   href="#table">table</a></code> element that is neither a <code><a
   href="#caption0">caption</a></code> element, a <code><a
   href="#colgroup">colgroup</a></code> element, nor a <code><a
   href="#thead0">thead</a></code> element, if any, or at the end of the
   table if there are no such elements, and then that new element must be
   returned.

  <p>The <dfn id=deletetfoot
   title=dom-table-deleteTFoot><code>deleteTFoot()</code></dfn> method must
   remove the first <code><a href="#tfoot0">tfoot</a></code> element child of
   the <code><a href="#table">table</a></code> element, if any.

  <p>The <dfn id=tbodies title=dom-table-tBodies><code>tBodies</code></dfn>
   attribute must return an <code><a
   href="#htmlcollection0">HTMLCollection</a></code> rooted at the <code><a
   href="#table">table</a></code> node, whose filter matches only <code><a
   href="#tbody">tbody</a></code> elements that are children of the <code><a
   href="#table">table</a></code> element.

  <p>The <dfn id=rows title=dom-table-rows><code>rows</code></dfn> attribute
   must return an <code><a href="#htmlcollection0">HTMLCollection</a></code>
   rooted at the <code><a href="#table">table</a></code> node, whose filter
   matches only <code><a href="#tr">tr</a></code> elements that are either
   children of the <code><a href="#table">table</a></code> element, or
   children of <code><a href="#thead0">thead</a></code>, <code><a
   href="#tbody">tbody</a></code>, or <code><a
   href="#tfoot0">tfoot</a></code> elements that are themselves children of
   the <code><a href="#table">table</a></code> element. The elements in the
   collection must be ordered such that those elements whose parent is a
   <code><a href="#thead0">thead</a></code> are included first, in tree
   order, followed by those elements whose parent is either a <code><a
   href="#table">table</a></code> or <code><a href="#tbody">tbody</a></code>
   element, again in tree order, followed finally by those elements whose
   parent is a <code><a href="#tfoot0">tfoot</a></code> element, still in
   tree order.

  <p>The behaviour of the <dfn id=insertrow
   title=dom-table-insertRow><code>insertRow(<var
   title="">index</var>)</code></dfn> method depends on the state of the
   table. When it is called, the method must act as required by the first
   item in the following list of conditions that describes the state of the
   table and the <var title="">index</var> argument:

  <dl class=switch>
   <dt>If <var title="">index</var> is less than -1 or greater than the
    number of elements in <code title=dom-table-rows><a
    href="#rows">rows</a></code> collection:

   <dd>The method must raise an <code>INDEX_SIZE_ERR</code> exception.

   <dt>If the <code title=dom-table-rows><a href="#rows">rows</a></code>
    collection has zero elements in it, and the <code><a
    href="#table">table</a></code> has no <code><a
    href="#tbody">tbody</a></code> elements in it:

   <dd>The method must create a <code><a href="#tbody">tbody</a></code>
    element, then create a <code><a href="#tr">tr</a></code> element, then
    append the <code><a href="#tr">tr</a></code> element to the <code><a
    href="#tbody">tbody</a></code> element, then append the <code><a
    href="#tbody">tbody</a></code> element to the <code><a
    href="#table">table</a></code> element, and finally return the <code><a
    href="#tr">tr</a></code> element.

   <dt>If the <code title=dom-table-rows><a href="#rows">rows</a></code>
    collection has zero elements in it:

   <dd>The method must create a <code><a href="#tr">tr</a></code> element,
    append it to the last <code><a href="#tbody">tbody</a></code> element in
    the table, and return the <code><a href="#tr">tr</a></code> element.

   <dt>If <var title="">index</var> is equal to -1 or equal to the number of
    items in <code title=dom-table-rows><a href="#rows">rows</a></code>
    collection:

   <dd>The method must create a <code><a href="#tr">tr</a></code> element,
    and append it to the parent of the last <code><a href="#tr">tr</a></code>
    element in the <code title=dom-table-rows><a href="#rows">rows</a></code>
    collection. Then, the newly created <code><a href="#tr">tr</a></code>
    element must be returned.

   <dt>Otherwise:

   <dd>The method must create a <code><a href="#tr">tr</a></code> element,
    insert it immediately before the <var title="">index</var>th <code><a
    href="#tr">tr</a></code> element in the <code title=dom-table-rows><a
    href="#rows">rows</a></code> collection, in the same parent, and finally
    must return the newly created <code><a href="#tr">tr</a></code> element.
  </dl>

  <p>The <dfn id=deleterow title=dom-table-deleteRow><code>deleteRow(<var
   title="">index</var>)</code></dfn> method must remove the <var
   title="">index</var>th element in the <code title=dom-table-rows><a
   href="#rows">rows</a></code> collection from its parent. If <var
   title="">index</var> is less than zero or greater than or equal to the
   number of elements in the <code title=dom-table-rows><a
   href="#rows">rows</a></code> collection, the method must instead raise an
   <code>INDEX_SIZE_ERR</code> exception.

  <h4 id=the-caption><span class=secno>3.15.2. </span>The <dfn
   id=caption0><code>caption</code></dfn> element</h4>
  <!-- element has no special category -->

  <dl class=element>
   <dt>Contexts in which this element may be used:

   <dd>As the first element child of a <code><a
    href="#table">table</a></code> element.

   <dt>Content model:

   <dd><a href="#significant" title="significant inline
    content">Significant</a> <a href="#strictly">strictly inline-level
    content</a>.

   <dt>Element-specific attributes:

   <dd>None.

   <dt>DOM interface:

   <dd>No difference from <code><a
    href="#htmlelement">HTMLElement</a></code>.
  </dl>

  <p>The <code><a href="#caption0">caption</a></code> element represents the
   title of the <code><a href="#table">table</a></code> that is its parent,
   if it has a parent and that is a <code><a href="#table">table</a></code>
   element.

  <p>The <code><a href="#caption0">caption</a></code> element takes part in
   the <a href="#table0">table model</a>.

  <h4 id=the-colgroup><span class=secno>3.15.3. </span>The <dfn
   id=colgroup><code>colgroup</code></dfn> element</h4>
  <!-- element has no special category -->

  <dl class=element>
   <dt>Contexts in which this element may be used:

   <dd>As a child of a <code><a href="#table">table</a></code> element, after
    any <code><a href="#caption0">caption</a></code> elements and before any
    <code><a href="#thead0">thead</a></code>, <code><a
    href="#tbody">tbody</a></code>, <code><a href="#tfoot0">tfoot</a></code>,
    and <code><a href="#tr">tr</a></code> elements.

   <dt>Content model:

   <dd>Zero or more <code><a href="#col">col</a></code> elements.

   <dt>Element-specific attributes:

   <dd><code title=attr-colgroup-span><a href="#span0">span</a></code>, but
    only if the element contains no <code><a href="#col">col</a></code>
    elements

   <dt>DOM interface:

   <dd>
    <pre
     class=idl>interface <dfn id=htmltablecolelement>HTMLTableColElement</dfn> : <a href="#htmlelement">HTMLElement</a> {
           attribute unsigned long <a href="#span1" title=dom-colgroup-span>span</a>;
};</pre>
  </dl>

  <p>The <code><a href="#colgroup">colgroup</a></code> element represents a
   <a href="#column0" title=concept-column-group>group</a> of one or more <a
   href="#column" title=concept-column>columns</a> in the <code><a
   href="#table">table</a></code> that is its parent, if it has a parent and
   that is a <code><a href="#table">table</a></code> element.

  <p>If the <code><a href="#colgroup">colgroup</a></code> element contains no
   <code><a href="#col">col</a></code> elements, then the element may have a
   <dfn id=span0 title=attr-colgroup-span><code>span</code></dfn> content
   attribute specified, whose value must be a <a href="#valid">valid
   non-negative integer</a> greater than zero. Its default value, which must
   be used if <a href="#rules" title="rules for parsing non-negative
   integers">parsing the attribute as a non-negative integer</a> returns
   either an error or zero, is 1.

  <p>The <code><a href="#colgroup">colgroup</a></code> element and its <code
   title=attr-colgroup-span><a href="#span0">span</a></code> attribute take
   part in the <a href="#table0">table model</a>.

  <p>The <dfn id=span1 title=dom-colgroup-span><code>span</code></dfn> DOM
   attribute must <a href="#reflect">reflect</a> the content attribute of the
   same name, with the exception that on setting, if the new value is 0, then
   an <code>INDEX_SIZE_ERR</code> exception must be raised.

  <h4 id=the-col><span class=secno>3.15.4. </span>The <dfn
   id=col><code>col</code></dfn> element</h4>
  <!-- element has no special category -->

  <dl class=element>
   <dt>Contexts in which this element may be used:

   <dd>As a child of a <code><a href="#colgroup">colgroup</a></code> element
    that doesn't have a <code title=attr-col-span><a
    href="#span2">span</a></code> attribute.

   <dt>Content model:

   <dd>Empty.

   <dt>Element-specific attributes:

   <dd><code title=attr-col-span><a href="#span2">span</a></code>

   <dt>DOM interface:

   <dd>
    <p><code><a href="#htmltablecolelement">HTMLTableColElement</a></code>,
     same as for <code><a href="#colgroup">colgroup</a></code> elements. This
     interface defines one member, <code title=dom-col-span><a
     href="#span3">span</a></code>.</p>
  </dl>

  <p>If a <code><a href="#col">col</a></code> element has a parent and that
   is a <code><a href="#colgroup">colgroup</a></code> element that itself has
   a parent that is a <code><a href="#table">table</a></code> element, then
   the <code><a href="#col">col</a></code> element represents one or more <a
   href="#column" title=concept-column>columns</a> in the <a href="#column0"
   title=concept-column-group>column group</a> represented by that <code><a
   href="#colgroup">colgroup</a></code>.

  <p>The element may have a <dfn id=span2
   title=attr-col-span><code>span</code></dfn> content attribute specified,
   whose value must be a <a href="#valid">valid non-negative integer</a>
   greater than zero. Its default value, which must be used if <a
   href="#rules" title="rules for parsing non-negative integers">parsing the
   attribute as a non-negative integer</a> returns either an error or zero,
   is 1.

  <p>The <code><a href="#col">col</a></code> element and its <code
   title=attr-col-span><a href="#span2">span</a></code> attribute take part
   in the <a href="#table0">table model</a>.

  <p>The <dfn id=span3 title=dom-col-span><code>span</code></dfn> DOM
   attribute must <a href="#reflect">reflect</a> the content attribute of the
   same name, with the exception that on setting, if the new value is 0, then
   an <code>INDEX_SIZE_ERR</code> exception must be raised.

  <h4 id=the-tbody><span class=secno>3.15.5. </span>The <dfn
   id=tbody><code>tbody</code></dfn> element</h4>
  <!-- element has no special category -->

  <dl class=element>
   <dt>Contexts in which this element may be used:

   <dd>As a child of a <code><a href="#table">table</a></code> element, after
    any <code><a href="#caption0">caption</a></code>, <code><a
    href="#colgroup">colgroup</a></code>, and <code><a
    href="#thead0">thead</a></code> elements, but only if there are no
    <code><a href="#tr">tr</a></code> elements that are children of the
    <code><a href="#table">table</a></code> element.

   <dt>Content model:

   <dd>One or more <code><a href="#tr">tr</a></code> elements

   <dt>Element-specific attributes:

   <dd>None.

   <dt>DOM interface:

   <dd>
    <pre
     class=idl>interface <dfn id=htmltablesectionelement>HTMLTableSectionElement</dfn> : <a href="#htmlelement">HTMLElement</a> {
  readonly attribute <a href="#htmlcollection0">HTMLCollection</a> <a href="#rows0" title=dom-tbody-rows>rows</a>;
  <a href="#htmlelement">HTMLElement</a> <a href="#insertrow0" title=dom-tbody-insertRow>insertRow</a>(in long index);
  void <a href="#deleterow0" title=dom-tbody-deleteRow>deleteRow</a>(in long index);
};</pre>

    <p>The <code><a
     href="#htmltablesectionelement">HTMLTableSectionElement</a></code>
     interface is also used for <code><a href="#thead0">thead</a></code> and
     <code><a href="#tfoot0">tfoot</a></code> elements.</p>
  </dl>

  <p>The <code><a href="#tbody">tbody</a></code> element represents a <a
   href="#row-group" title=concept-row-group>block</a> of <a href="#row0"
   title=concept-row>rows</a> that consist of a body of data for the parent
   <code><a href="#table">table</a></code> element, if the <code><a
   href="#tbody">tbody</a></code> element has a parent and it is a <code><a
   href="#table">table</a></code>.

  <p>The <code><a href="#tbody">tbody</a></code> element takes part in the <a
   href="#table0">table model</a>.

  <p>The <dfn id=rows0 title=dom-tbody-rows><code>rows</code></dfn> attribute
   must return an <code><a href="#htmlcollection0">HTMLCollection</a></code>
   rooted at the element, whose filter matches only <code><a
   href="#tr">tr</a></code> elements that are children of the element.

  <p>The <dfn id=insertrow0 title=dom-tbody-insertRow><code>insertRow(<var
   title="">index</var>)</code></dfn> method must, when invoked on an element
   <var title="">table section</var>, act as follows:

  <p>If <var title="">index</var> is less than -1 or greater than the number
   of elements in the <code title=dom-tbody-rows><a
   href="#rows0">rows</a></code> collection, the method must raise an
   <code>INDEX_SIZE_ERR</code> exception.

  <p>If <var title="">index</var> is equal to -1 or equal to the number of
   items in the <code title=dom-tbody-rows><a href="#rows0">rows</a></code>
   collection, the method must create a <code><a href="#tr">tr</a></code>
   element, append it to the element <var title="">table section</var>, and
   return the newly created <code><a href="#tr">tr</a></code> element.

  <p>Otherwise, the method must create a <code><a href="#tr">tr</a></code>
   element, insert it as a child of the <var title="">table section</var>
   element, immediately before the <var title="">index</var>th <code><a
   href="#tr">tr</a></code> element in the <code title=dom-tbody-rows><a
   href="#rows0">rows</a></code> collection, and finally must return the
   newly created <code><a href="#tr">tr</a></code> element.

  <p>The <dfn id=deleterow0 title=dom-tbody-deleteRow><code>deleteRow(<var
   title="">index</var>)</code></dfn> method must remove the <var
   title="">index</var>th element in the <code title=dom-tbody-rows><a
   href="#rows0">rows</a></code> collection from its parent. If <var
   title="">index</var> is less than zero or greater than or equal to the
   number of elements in the <code title=dom-tbody-rows><a
   href="#rows0">rows</a></code> collection, the method must instead raise an
   <code>INDEX_SIZE_ERR</code> exception.

  <h4 id=the-thead><span class=secno>3.15.6. </span>The <dfn
   id=thead0><code>thead</code></dfn> element</h4>
  <!-- element has no special category -->

  <dl class=element>
   <dt>Contexts in which this element may be used:

   <dd>As a child of a <code><a href="#table">table</a></code> element, after
    any <code><a href="#caption0">caption</a></code>, and <code><a
    href="#colgroup">colgroup</a></code> elements and before any <code><a
    href="#tbody">tbody</a></code>, <code><a href="#tfoot0">tfoot</a></code>,
    and <code><a href="#tr">tr</a></code> elements, but only if there are no
    other <code><a href="#thead0">thead</a></code> elements that are children
    of the <code><a href="#table">table</a></code> element.

   <dt>Content model:

   <dd>One or more <code><a href="#tr">tr</a></code> elements

   <dt>Element-specific attributes:

   <dd>None.

   <dt>DOM interface:

   <dd><code><a
    href="#htmltablesectionelement">HTMLTableSectionElement</a></code>, as
    defined for <code><a href="#tbody">tbody</a></code> elements.
  </dl>

  <p>The <code><a href="#thead0">thead</a></code> element represents the <a
   href="#row-group" title=concept-row-group>block</a> of <a href="#row0"
   title=concept-row>rows</a> that consist of the column labels (headers) for
   the parent <code><a href="#table">table</a></code> element, if the
   <code><a href="#thead0">thead</a></code> element has a parent and it is a
   <code><a href="#table">table</a></code>.

  <p>The <code><a href="#thead0">thead</a></code> element takes part in the
   <a href="#table0">table model</a>.

  <h4 id=the-tfoot><span class=secno>3.15.7. </span>The <dfn
   id=tfoot0><code>tfoot</code></dfn> element</h4>
  <!-- element has no special category -->

  <dl class=element>
   <dt>Contexts in which this element may be used:

   <dd>As a child of a <code><a href="#table">table</a></code> element, after
    any <code><a href="#caption0">caption</a></code>, <code><a
    href="#colgroup">colgroup</a></code>, and <code><a
    href="#thead0">thead</a></code> elements and before any <code><a
    href="#tbody">tbody</a></code> and <code><a href="#tr">tr</a></code>
    elements, but only if there are no other <code><a
    href="#tfoot0">tfoot</a></code> elements that are children of the
    <code><a href="#table">table</a></code> element.

   <dd>As a child of a <code><a href="#table">table</a></code> element, after
    any <code><a href="#caption0">caption</a></code>, <code><a
    href="#colgroup">colgroup</a></code>, <code><a
    href="#thead0">thead</a></code>, <code><a href="#tbody">tbody</a></code>,
    and <code><a href="#tr">tr</a></code> elements, but only if there are no
    other <code><a href="#tfoot0">tfoot</a></code> elements that are children
    of the <code><a href="#table">table</a></code> element.

   <dt>Content model:

   <dd>One or more <code><a href="#tr">tr</a></code> elements

   <dt>Element-specific attributes:

   <dd>None.

   <dt>DOM interface:

   <dd><code><a
    href="#htmltablesectionelement">HTMLTableSectionElement</a></code>, as
    defined for <code><a href="#tbody">tbody</a></code> elements.
  </dl>

  <p>The <code><a href="#tfoot0">tfoot</a></code> element represents the <a
   href="#row-group" title=concept-row-group>block</a> of <a href="#row0"
   title=concept-row>rows</a> that consist of the column summaries (footers)
   for the parent <code><a href="#table">table</a></code> element, if the
   <code><a href="#tfoot0">tfoot</a></code> element has a parent and it is a
   <code><a href="#table">table</a></code>.

  <p>The <code><a href="#tfoot0">tfoot</a></code> element takes part in the
   <a href="#table0">table model</a>.

  <h4 id=the-tr><span class=secno>3.15.8. </span>The <dfn
   id=tr><code>tr</code></dfn> element</h4>
  <!-- element has no special category -->

  <dl class=element>
   <dt>Contexts in which this element may be used:

   <dd>As a child of a <code><a href="#thead0">thead</a></code> element.

   <dd>As a child of a <code><a href="#tbody">tbody</a></code> element.

   <dd>As a child of a <code><a href="#tfoot0">tfoot</a></code> element.

   <dd>As a child of a <code><a href="#table">table</a></code> element, after
    any <code><a href="#caption0">caption</a></code>, <code><a
    href="#colgroup">colgroup</a></code>, and <code><a
    href="#thead0">thead</a></code> elements, but only if there are no
    <code><a href="#tbody">tbody</a></code> elements that are children of the
    <code><a href="#table">table</a></code> element.

   <dt>Content model:

   <dd>One or more <code><a href="#td">td</a></code> or <code><a
    href="#th">th</a></code> elements

   <dt>Element-specific attributes:

   <dd>None.

   <dt>DOM interface:

   <dd>
    <pre
     class=idl>interface <dfn id=htmltablerowelement>HTMLTableRowElement</dfn> : <a href="#htmlelement">HTMLElement</a> {
  readonly attribute long <a href="#rowindex" title=dom-tr-rowIndex>rowIndex</a>;
  readonly attribute long <a href="#rowindex0" title=dom-tr-sectionRowIndex>sectionRowIndex</a>;
  readonly attribute <a href="#htmlcollection0">HTMLCollection</a> <a href="#cells" title=dom-tr-cells>cells</a>;
  <a href="#htmlelement">HTMLElement</a> <a href="#insertcell" title=dom-tr-insertCell>insertCell</a>(in long index);
  void <span>deleteCell</span>(in long index);
};</pre>
  </dl>

  <p>The <code><a href="#tr">tr</a></code> element represents a <a
   href="#row0" title=concept-row>row</a> of <a href="#cell"
   title=concept-cell>cells</a> in a <a href="#table1"
   title=concept-table>table</a>.

  <p>The <code><a href="#tr">tr</a></code> element takes part in the <a
   href="#table0">table model</a>.

  <p>The <dfn id=rowindex title=dom-tr-rowIndex><code>rowIndex</code></dfn>
   element must, if the element has a parent <code><a
   href="#table">table</a></code> element, or a parent <code><a
   href="#tbody">tbody</a></code>, <code><a href="#thead0">thead</a></code>,
   or <code><a href="#tfoot0">tfoot</a></code> element and a
   <em>grandparent</em> <code><a href="#table">table</a></code> element,
   return the index of the <code><a href="#tr">tr</a></code> element in that
   <code><a href="#table">table</a></code> element's <code
   title=dom-table-rows><a href="#rows">rows</a></code> collection. If there
   is no such <code><a href="#table">table</a></code> element, then the
   attribute must return 0.

  <p>The <dfn id=rowindex0
   title=dom-tr-sectionRowIndex><code>rowIndex</code></dfn> DOM attribute
   must, if the element has a parent <code><a href="#table">table</a></code>,
   <code><a href="#tbody">tbody</a></code>, <code><a
   href="#thead0">thead</a></code>, or <code><a
   href="#tfoot0">tfoot</a></code> element, return the index of the <code><a
   href="#tr">tr</a></code> element in the parent element's <code
   title="">rows</code> collection (for tables, that's the <code
   title=dom-table-rows><a href="#rows">rows</a></code> collection; for table
   sections, that's the <code title=dom-tbody-rows><a
   href="#rows0">rows</a></code> collection). If there is no such parent
   element, then the attribute must return 0.

  <p>The <dfn id=cells title=dom-tr-cells><code>cells</code></dfn> attribute
   must return an <code><a href="#htmlcollection0">HTMLCollection</a></code>
   rooted at the <code><a href="#tr">tr</a></code> element, whose filter
   matches only <code><a href="#td">td</a></code> and <code><a
   href="#th">th</a></code> elements that are children of the <code><a
   href="#tr">tr</a></code> element.

  <p>The <dfn id=insertcell title=dom-tr-insertCell><code>insertCell(<var
   title="">index</var>)</code></dfn> method must act as follows:

  <p>If <var title="">index</var> is less than -1 or greater than the number
   of elements in the <code title=dom-tr-cells><a
   href="#cells">cells</a></code> collection, the method must raise an
   <code>INDEX_SIZE_ERR</code> exception.

  <p>If <var title="">index</var> is equal to -1 or equal to the number of
   items in <code title=dom-tr-cells><a href="#cells">cells</a></code>
   collection, the method must create a <code><a href="#td">td</a></code>
   element, append it to the <code><a href="#tr">tr</a></code> element, and
   return the newly created <code><a href="#td">td</a></code> element.

  <p>Otherwise, the method must create a <code><a href="#td">td</a></code>
   element, insert it as a child of the <code><a href="#tr">tr</a></code>
   element, immediately before the <var title="">index</var>th <code><a
   href="#td">td</a></code> or <code><a href="#th">th</a></code> element in
   the <code title=dom-tr-cells><a href="#cells">cells</a></code> collection,
   and finally must return the newly created <code><a
   href="#td">td</a></code> element.

  <p>The <dfn id=deletecell title=dom-tr-deleteCell><code>deleteCell(<var
   title="">index</var>)</code></dfn> method must remove the <var
   title="">index</var>th element in the <code title=dom-tr-cells><a
   href="#cells">cells</a></code> collection from its parent. If <var
   title="">index</var> is less than zero or greater than or equal to the
   number of elements in the <code title=dom-tr-cells><a
   href="#cells">cells</a></code> collection, the method must instead raise
   an <code>INDEX_SIZE_ERR</code> exception.

  <h4 id=the-td><span class=secno>3.15.9. </span>The <dfn
   id=td><code>td</code></dfn> element</h4>
  <!-- element has no special category -->

  <dl class=element>
   <dt>Contexts in which this element may be used:

   <dd>As a child of a <code><a href="#tr">tr</a></code> element.

   <dt>Content model:

   <dd>Zero or more <a href="#block-level0">block-level elements</a>, or <a
    href="#inline-level0">inline-level content</a> (but not both).

   <dt>Element-specific attributes:

   <dd><code title=attr-td-colspan><a href="#colspan">colspan</a></code>

   <dd><code title=attr-td-rowspan><a href="#rowspan">rowspan</a></code>

   <dt>DOM interface:

   <dd>
    <pre
     class=idl>interface <dfn id=htmltablecellelement>HTMLTableCellElement</dfn> : <a href="#htmlelement">HTMLElement</a> {
           attribute long <a href="#colspan0" title=dom-td-colSpan>colSpan</a>;
           attribute long <a href="#rowspan0" title=dom-td-rowSpan>rowSpan</a>;
  readonly attribute long <a href="#cellindex" title=dom-td-cellIndex>cellIndex</a>;
};</pre>
  </dl>

  <p>The <code><a href="#td">td</a></code> element represents a data <a
   href="#cell" title=concept-cell>cell</a> in a table.

  <p>The <code><a href="#td">td</a></code> element may have a <dfn id=colspan
   title=attr-td-colspan><code>colspan</code></dfn> content attribute
   specified, whose value must be a <a href="#valid">valid non-negative
   integer</a> greater than zero. Its default value, which must be used if <a
   href="#rules" title="rules for parsing non-negative integers">parsing the
   attribute as a non-negative integer</a> returns either an error or zero,
   is 1.

  <p>The <code><a href="#td">td</a></code> element may also have a <dfn
   id=rowspan title=attr-td-rowspan><code>rowspan</code></dfn> content
   attribute specified, whose value must be a <a href="#valid">valid
   non-negative integer</a>. Its default value, which must be used if <a
   href="#rules" title="rules for parsing non-negative integers">parsing the
   attribute as a non-negative integer</a> returns an error, is also 1.

  <p>The <code><a href="#td">td</a></code> element and its <code
   title=attr-td-colspan><a href="#colspan">colspan</a></code> and <code
   title=attr-td-rowspan><a href="#rowspan">rowspan</a></code> attributes
   take part in the <a href="#table0">table model</a>.

  <p>The <dfn id=colspan0 title=dom-td-colspan><code>colspan</code></dfn> DOM
   attribute must <a href="#reflect">reflect</a> the content attribute of the
   same name, with the exception that on setting, if the new value is 0, then
   an <code>INDEX_SIZE_ERR</code> exception must be raised.

  <p>The <dfn id=rowspan0 title=dom-td-rowspan><code>rowspan</code></dfn> DOM
   attribute must <a href="#reflect">reflect</a> the content attribute of the
   same name.

  <p>The <dfn id=cellindex
   title=dom-td-cellIndex><code>cellIndex</code></dfn> DOM attribute must, if
   the element has a parent <code><a href="#tr">tr</a></code> element, return
   the index of the cell's element in the parent element's <code
   title=dom-tr-cells><a href="#cells">cells</a></code> collection. If there
   is no such parent element, then the attribute must return 0.

  <h4 id=the-th><span class=secno>3.15.10. </span>The <dfn
   id=th><code>th</code></dfn> element</h4>
  <!-- element has no special category -->

  <dl class=element>
   <dt>Contexts in which this element may be used:

   <dd>As a child of a <code><a href="#tr">tr</a></code> element.

   <dt>Content model:

   <dd>Zero or more <a href="#block-level0">block-level elements</a>, or <a
    href="#inline-level0">inline-level content</a> (but not both).

   <dt>Element-specific attributes:

   <dd><code title=attr-th-colspan><a href="#colspan1">colspan</a></code>

   <dd><code title=attr-th-rowspan><a href="#rowspan1">rowspan</a></code>

   <dd><code title=attr-th-scope><a href="#scope0">scope</a></code>

   <dt>DOM interface:

   <dd>
    <pre
     class=idl>interface <dfn id=htmltableheadercellelement>HTMLTableHeaderCellElement</dfn> : <a href="#htmltablecellelement">HTMLTableCellElement</a> {
           attribute DOMString <a href="#scope1" title=dom-th-scope>scope</a>;
};</pre>
  </dl>

  <p>The <code><a href="#th">th</a></code> element represents a header <a
   href="#cell" title=concept-cell>cell</a> in a table.

  <p>The <code><a href="#th">th</a></code> element may have a <dfn
   id=colspan1 title=attr-th-colspan><code>colspan</code></dfn> content
   attribute specified, whose value must be a <a href="#valid">valid
   non-negative integer</a> greater than zero. Its default value, which must
   be used if <a href="#rules" title="rules for parsing non-negative
   integers">parsing the attribute as a non-negative integer</a> returns
   either an error or zero, is 1.

  <p>The <code><a href="#th">th</a></code> element may also have a <dfn
   id=rowspan1 title=attr-th-rowspan><code>rowspan</code></dfn> content
   attribute specified, whose value must be a <a href="#valid">valid
   non-negative integer</a>. Its default value, which must be used if <a
   href="#rules" title="rules for parsing non-negative integers">parsing the
   attribute as a non-negative integer</a> returns an error, is also 1.

  <p>The <code><a href="#th">th</a></code> element may have a <dfn id=scope0
   title=attr-th-scope><code>scope</code></dfn> content attribute specified.
   The <code title=attr-th-scope><a href="#scope0">scope</a></code> attribute
   is an <a href="#enumerated">enumerated attribute</a> with five states,
   four of which have explicit keywords:

  <dl>
   <dt>The <dfn id=row title=attr-th-scope-row><code>row</code></dfn>
    keyword, which maps to the <em>row</em> state

   <dd>The <em>row</em> state means the header cell applies to all the
    remaining cells in the row.

   <dt>The <dfn id=col0 title=attr-th-scope-col><code>col</code></dfn>
    keyword, which maps to the <em>column</em> state

   <dd>The <em>column</em> state means the header cell applies to all the
    remaining cells in the column.

   <dt>The <dfn id=rowgroup
    title=attr-th-scope-rowgroup><code>rowgroup</code></dfn> keyword, which
    maps to the <em>row group</em> state

   <dd>The <em>row group</em> state means the header cell applies to all the
    remaining cells in the row group.

   <dt>The <dfn id=colgroup0
    title=attr-th-scope-colgroup><code>colgroup</code></dfn> keyword, which
    maps to the <em>column group</em> state

   <dd>The <em>column group</em> state means the header cell applies to all
    the remaining cells in the column group.

   <dt>The <em>auto</em> state

   <dd>The <em>auto</em> state makes the header cell apply to a set of cells
    selected based on context.
  </dl>

  <p>The <code title=attr-th-scope><a href="#scope0">scope</a></code>
   attribute's <em>missing value default</em> is the <em>auto</em> state.

  <p>The exact effect of these values is described in detail in the <a
   href="#algorithm2">algorithm for assigning header cells to data cells</a>,
   which user agents must apply to determine the relationships between data
   cells and header cells.

  <p>The <code><a href="#th">th</a></code> element and its <code
   title=attr-th-colspan><a href="#colspan1">colspan</a></code>, <code
   title=attr-th-rowspan><a href="#rowspan1">rowspan</a></code>, and <code
   title=attr-th-scope><a href="#scope0">scope</a></code> attributes take
   part in the <a href="#table0">table model</a>.

  <p>The <dfn id=scope1 title=dom-th-scope><code>scope</code></dfn> DOM
   attribute must <a href="#reflect">reflect</a> the content attribute of the
   same name.

  <p>The <code><a
   href="#htmltableheadercellelement">HTMLTableHeaderCellElement</a></code>
   interface inherits from the <code><a
   href="#htmltablecellelement">HTMLTableCellElement</a></code> interface and
   therefore also has the DOM attributes defined above in the <code><a
   href="#td">td</a></code> section.

  <h4 id=processing><span class=secno>3.15.11. </span>Processing model</h4>

  <p>The various table elements and their content attributes together define
   the <dfn id=table0>table model</dfn>.

  <p>A <dfn id=table1 title=concept-table>table</dfn> consists of cells
   aligned on a two-dimensional grid of <dfn id=slots
   title=concept-slots>slots</dfn> with coordinates (<var title="">x</var>,
   <var title="">y</var>). The grid is finite, and is either empty or has one
   or more slots. If the grid has one or more slots, then the <var
   title="">x</var> coordinates are always in the range
   <span>1&nbsp;&le;&nbsp;<var title="">x</var>&nbsp;&le;&nbsp;<var
   title="">x<sub title="">max</sub></var></span>, and the <var
   title="">y</var> coordinates are always in the range
   <span>1&nbsp;&le;&nbsp;<var title="">y</var>&nbsp;&le;&nbsp;<var
   title="">y<sub title="">max</sub></var></span>. If one or both of <var
   title="">x<sub title="">max</sub></var> and <var title="">y<sub
   title="">max</sub></var> are zero, then the table is empty (has no slots).
   Tables correspond to <code><a href="#table">table</a></code> elements.

  <p>A <dfn id=cell title=concept-cell>cell</dfn> is a set of slots anchored
   at a slot (<var title="">cell<sub title="">x</sub></var>, <var
   title="">cell<sub title="">y</sub></var>), and with a particular <var
   title="">width</var> and <var title="">height</var> such that the cell
   covers all the slots with coordinates (<var title="">x</var>, <var
   title="">y</var>) where <span><var title="">cell<sub
   title="">x</sub></var>&nbsp;&le;&nbsp;<var
   title="">x</var>&nbsp;&lt;&nbsp;<var title="">cell<sub
   title="">x</sub></var>+<var title="">width</var></span> and <span><var
   title="">cell<sub title="">y</sub></var>&nbsp;&le;&nbsp;<var
   title="">y</var>&nbsp;&lt;&nbsp;<var title="">cell<sub
   title="">y</sub></var>+<var title="">height</var></span>. Cell can either
   be <em>data cells</em> or <em>header cells</em>. Data cells correspond to
   <code><a href="#td">td</a></code> elements, and have zero or more
   associated header cells. Header cells correspond to <code><a
   href="#th">th</a></code> elements.

  <p>A <dfn id=row0 title=concept-row>row</dfn> is a complete set of slots
   from <span><var title="">x</var>=1</span> to <span><var
   title="">x</var>=<var title="">x<sub title="">max</sub></var></span>, for
   a particular value of <var title="">y</var>. Rows correspond to <code><a
   href="#tr">tr</a></code> elements.

  <p>A <dfn id=column title=concept-column>column</dfn> is a complete set of
   slots from <span><var title="">y</var>=1</span> to <span><var
   title="">y</var>=<var title="">y<sub title="">max</sub></var></span>, for
   a particular value of <var title="">x</var>. Columns can correspond to
   <code><a href="#col">col</a></code> elements, but in the absense of
   <code><a href="#col">col</a></code> elements are implied.

  <p>A <dfn id=row-group title=concept-row-group>row group</dfn> is a set of
   <a href="#row0" title=concept-row>rows</a> anchored at a slot (1, <var
   title="">group<sub title="">y</sub></var>) with a particular <var
   title="">height</var> such that the row group covers all the slots with
   coordinates (<var title="">x</var>, <var title="">y</var>) where
   <span>1&nbsp;&le;&nbsp;<var title="">x</var>&nbsp;&lt;&nbsp;<var
   title="">x<sub title="">max</sub></var></span> and <span><var
   title="">group<sub title="">y</sub></var>&nbsp;&le;&nbsp;<var
   title="">y</var>&nbsp;&lt;&nbsp;<var title="">group<sub
   title="">y</sub></var>+<var title="">height</var></span>. Row groups
   correspond to <code><a href="#tbody">tbody</a></code>, <code><a
   href="#thead0">thead</a></code>, and <code><a
   href="#tfoot0">tfoot</a></code> elements. Not every row is necessarily in
   a row group.

  <p>A <dfn id=column0 title=concept-column-group>column group</dfn> is a set
   of <a href="#column" title=concept-column>columns</a> anchored at a slot
   (<var title="">group<sub title="">x</sub></var>, 1) with a particular <var
   title="">width</var> such that the column group covers all the slots with
   coordinates (<var title="">x</var>, <var title="">y</var>) where
   <span><var title="">group<sub title="">x</sub></var>&nbsp;&le;&nbsp;<var
   title="">x</var>&nbsp;&lt;&nbsp;<var title="">group<sub
   title="">x</sub></var>+<var title="">width</var></span> and
   <span>1&nbsp;&le;&nbsp;<var title="">y</var>&nbsp;&lt;&nbsp;<var
   title="">y<sub title="">max</sub></var></span>. Column groups correspond
   to <code><a href="#colgroup">colgroup</a></code> elements. Not every
   column is necessarily in a column group.

  <p><a href="#row-group" title=concept-row-group>Row groups</a> cannot
   overlap each other. Similarly, <a href="#column0"
   title=concept-column-group>column groups</a> cannot overlap each other.

  <p>A <a href="#cell" title=concept-cell>cell</a> cannot cover slots that
   are from two or more <a href="#row-group" title=concept-row-group>row
   groups</a>. It is, however, possible for a cell to be in multiple <a
   href="#column0" title=concept-column-group>column groups</a>. All the
   slots that form part of one cell are part of zero or one <a
   href="#row-group" title=concept-row-group>row groups</a> and zero or more
   <a href="#column0" title=concept-column-group>column groups</a>.

  <p>In addition to <a href="#cell" title=concept-cell>cells</a>, <a
   href="#column" title=concept-column>columns</a>, <a href="#row0"
   title=concept-row>rows</a>, <a href="#row-group"
   title=concept-row-group>row groups</a>, and <a href="#column0"
   title=concept-column-group>column groups</a>, <a href="#table1"
   title=concept-table>tables</a> can have a <code><a
   href="#caption0">caption</a></code> element associated with them. This
   gives the table a heading, or legend.

  <p>A <dfn id=table2>table model error</dfn> is an error with the data
   represented by <code><a href="#table">table</a></code> elements and their
   descendants. Documents must not have table model errors.

  <h5 id=forming><span class=secno>3.15.11.1. </span>Forming a table</h5>

  <p>To determine which elements correspond to which slots in a <a
   href="#table1" title=concept-table>table</a> associated with a <code><a
   href="#table">table</a></code> element, to determine the dimensions of the
   table (<var title="">x<sub title="">max</sub></var> and <var
   title="">y<sub title="">max</sub></var>), and to determine if there are
   any <a href="#table2" title="table model error">table model errors</a>,
   user agents must use the following algorithm:

  <ol>
   <li>
    <p>Let <var title="">x<sub title="">max</sub></var> be zero.</p>

   <li>
    <p>Let <var title="">y<sub title="">max</sub></var> be zero.</p>

   <li>
    <p>Let <var title="">the table</var> be the <a href="#table1"
     title=concept-table>table</a> represented by the <code><a
     href="#table">table</a></code> element. The <var title="">x<sub
     title="">max</sub></var> and <var title="">y<sub
     title="">max</sub></var> variables give <var title="">the table</var>'s
     extent. <var title="">The table</var> is initially empty.</p>

   <li>
    <p>If the <code><a href="#table">table</a></code> element has no table
     children, then return <var title="">the table</var> (which will be
     empty), and abort these steps.</p>

   <li>
    <p>Let the <var title="">current element</var> be the first element child
     of the <code><a href="#table">table</a></code> element.</p>

    <p>If a step in this algorithm ever requires the <var title="">current
     element</var> to be advanced to the next child of the <code><a
     href="#table">table</a></code> when there is no such next child, then
     the algorithm must be aborted at that point and the algorithm must
     return <var title="">the table</var>.</p>

   <li>
    <p>While the <var title="">current element</var> is not one of the
     following elements, advance the <var title="">current element</var> to
     the next child of the <code><a href="#table">table</a></code>:</p>

    <ul class=brief>
     <li><code><a href="#caption0">caption</a></code>

     <li><code><a href="#colgroup">colgroup</a></code>

     <li><code><a href="#thead0">thead</a></code>

     <li><code><a href="#tbody">tbody</a></code>

     <li><code><a href="#tfoot0">tfoot</a></code>

     <li><code><a href="#tr">tr</a></code>
    </ul>

   <li>
    <p>If the <var title="">current element</var> is a <code><a
     href="#caption0">caption</a></code>, then that is the <code><a
     href="#caption0">caption</a></code> element associated with <var
     title="">the table</var>. Otherwise, it has no associated <code><a
     href="#caption0">caption</a></code> element.</p>

   <li>
    <p>If the <var title="">current element</var> is a <code><a
     href="#caption0">caption</a></code>, then while the <var
     title="">current element</var> is not one of the following elements,
     advance the <var title="">current element</var> to the next child of the
     <code><a href="#table">table</a></code>:</p>

    <ul class=brief>
     <li><code><a href="#colgroup">colgroup</a></code>

     <li><code><a href="#thead0">thead</a></code>

     <li><code><a href="#tbody">tbody</a></code>

     <li><code><a href="#tfoot0">tfoot</a></code>

     <li><code><a href="#tr">tr</a></code>
    </ul>

    <p>(Otherwise, the <var title="">current element</var> will already be
     one of those elements.)</p>

   <li>
    <p>If the <var title="">current element</var> is a <code><a
     href="#colgroup">colgroup</a></code>, follow these substeps:</p>

    <ol>
     <li>
      <p>Let <var title="">next column</var> be 1.</p>

     <li>
      <p><em>Column groups.</em> Process the <var title="">current
       element</var> according to the appropriate one of the following two
       cases:</p>

      <dl class=switch>
       <dt>If the <var title="">current element</var> has any <code><a
        href="#col">col</a></code> element children

       <dd>
        <p>Follow these steps:</p>

        <ol>
         <li>
          <p>Let <var title="">x<sub title="">start</sub></var> have the
           value <span><var title="">x<sub title="">max</sub></var>+1</span>.</p>

         <li>
          <p>Let the <var title="">current column</var> be the first <code><a
           href="#col">col</a></code> element child of the <code><a
           href="#colgroup">colgroup</a></code> element.</p>

         <li>
          <p><em>Columns.</em> If the <var title="">current column</var>
           <code><a href="#col">col</a></code> element has a <code
           title=attr-col-span><a href="#span2">span</a></code> attribute,
           then parse its value using the <a href="#rules">rules for parsing
           non-negative integers</a>.</p>

          <p>If the result of parsing the value is not an error or zero, then
           let <var title="">span</var> be that value.</p>

          <p>Otherwise, if the <code><a href="#col">col</a></code> element
           has no <code title=attr-col-span><a href="#span2">span</a></code>
           attribute, or if trying to parse the attribute's value resulted in
           an error, then let <var title="">span</var> be 1.</p>

         <li>
          <p>Increase <var title="">x<sub title="">max</sub></var> by <var
           title="">span</var>.</p>

         <li>
          <p>Let the last <var title="">span</var> <a href="#column"
           title=concept-column>columns</a> in <var title="">the table</var>
           correspond to the <var title="">current column</var> <code><a
           href="#col">col</a></code> element.</p>

         <li>
          <p>If <var title="">current column</var> is not the last <code><a
           href="#col">col</a></code> element child of the <code><a
           href="#colgroup">colgroup</a></code> element, then let the <var
           title="">current column</var> be the next <code><a
           href="#col">col</a></code> element child of the <code><a
           href="#colgroup">colgroup</a></code> element, and return to the
           third step of this innermost group of steps (columns).</p>

         <li>
          <p>Let all the last <a href="#column"
           title=concept-column>columns</a> in <var title="">the table</var>
           from <span>x=<var title="">x<sub title="">start</sub></var></span>
           to <span>x=<var title="">x<sub title="">max</sub></var></span>
           form a new <a href="#column0" title=concept-column-group>column
           group</a>, anchored at the slot (<var title="">x<sub
           title="">start</sub></var>, 1), with width <var title="">x<sub
           title="">max</sub></var>-<var title="">x<sub
           title="">start</sub></var>-1, corresponding to the <code><a
           href="#colgroup">colgroup</a></code> element.</p>
        </ol>

       <dt>If the <var title="">current element</var> has no <code><a
        href="#col">col</a></code> element children

       <dd>
        <ol>
         <li>
          <p>If the <code><a href="#colgroup">colgroup</a></code> element has
           a <code title=attr-colgroup-span><a href="#span0">span</a></code>
           attribute, then parse its value using the <a href="#rules">rules
           for parsing non-negative integers</a>.</p>

          <p>If the result of parsing the value is not an error or zero, then
           let <var title="">span</var> be that value.</p>

          <p>Otherwise, if the <code><a href="#colgroup">colgroup</a></code>
           element has no <code title=attr-col-span><a
           href="#span2">span</a></code> attribute, or if trying to parse the
           attribute's value resulted in an error, then let <var
           title="">span</var> be 1.</p>

         <li>
          <p>Increase <var title="">x<sub title="">max</sub></var> by <var
           title="">span</var>.</p>

         <li>
          <p>Let the last <var title="">span</var> <a href="#column"
           title=concept-column>columns</a> in <var title="">the table</var>
           form a new <a href="#column0" title=concept-column-group>column
           group</a>, anchored at the slot (<var title="">x<sub
           title="">max</sub></var>-<var title="">span</var>+1, 1), with
           width <var title="">span</var>, corresponding to the <code><a
           href="#colgroup">colgroup</a></code> element.</p>
        </ol>
      </dl>

     <li>
      <p>Advance the <var title="">current element</var> to the next child of
       the <code><a href="#table">table</a></code>.</p>

     <li>
      <p>While the <var title="">current element</var> is not one of the
       following elements, advance the <var title="">current element</var> to
       the next child of the <code><a href="#table">table</a></code>:</p>

      <ul class=brief>
       <li><code><a href="#colgroup">colgroup</a></code>

       <li><code><a href="#thead0">thead</a></code>

       <li><code><a href="#tbody">tbody</a></code>

       <li><code><a href="#tfoot0">tfoot</a></code>

       <li><code><a href="#tr">tr</a></code>
      </ul>

     <li>
      <p>If the <var title="">current element</var> is a <code><a
       href="#colgroup">colgroup</a></code> element, jump to step 2 in these
       substeps (column groups).</p>
    </ol>

   <li>
    <p>Let <var title="">y<sub title="">current</sub></var> be zero. When the
     algorithm is aborted, if <var title="">y<sub
     title="">current</sub></var> does not equal <var title="">y<sub
     title="">max</sub></var>, then that is a <a href="#table2">table model
     error</a>.</p>

   <li>
    <p>Let the <var title="">list of downward-growing cells</var> be an empty
     list.</p>

   <li>
    <p><em>Rows.</em> While the <var title="">current element</var> is not
     one of the following elements, advance the <var title="">current
     element</var> to the next child of the <code><a
     href="#table">table</a></code>:</p>

    <ul class=brief>
     <li><code><a href="#thead0">thead</a></code>

     <li><code><a href="#tbody">tbody</a></code>

     <li><code><a href="#tfoot0">tfoot</a></code>

     <li><code><a href="#tr">tr</a></code>
    </ul>

   <li>
    <p>If the <var title="">current element</var> is a <code><a
     href="#tr">tr</a></code>, then run the <a href="#algorithm0">algorithm
     for processing rows</a> (defined below), then return to the previous
     step (rows).</p>

   <li>
    <p>Otherwise, run the <a href="#algorithm">algorithm for ending a row
     group</a>.</p>

   <li>
    <p>Let <var title="">y<sub title="">start</sub></var> have the value
     <span><var title="">y<sub title="">max</sub></var>+1</span>.</p>

   <li>
    <p>For each <code><a href="#tr">tr</a></code> element that is a child of
     the <var title="">current element</var>, in tree order, run the <a
     href="#algorithm0">algorithm for processing rows</a> (defined below).</p>

   <li> <!-- if we added any rows, make them part of a row group -->
    <p>If <span><var title="">y<sub
     title="">max</sub></var>&nbsp;&ge;&nbsp;<var title="">y<sub
     title="">start</sub></var></span>, then let all the last <a href="#row0"
     title=concept-row>rows</a> in <var title="">the table</var> from
     <span>y=<var title="">y<sub title="">start</sub></var></span> to
     <span>y=<var title="">y<sub title="">max</sub></var></span> form a new
     <a href="#row-group" title=concept-row-group>row group</a>, anchored at
     the slot with coordinate (1, <var title="">y<sub
     title="">start</sub></var>), with height <var title="">y<sub
     title="">max</sub></var>-<var title="">y<sub
     title="">start</sub></var>+1, corresponding to the <var title="">current
     element</var>.</p>

   <li>
    <p>Run the <a href="#algorithm">algorithm for ending a row group</a>
     again.</p>

   <li>
    <p>Return to step 12 (rows).</p>
  </ol>

  <p>The <dfn id=algorithm>algorithm for ending a row group</dfn>, which is
   invoked by the set of steps above when starting and eding a block of rows,
   is:

  <ol>
   <li>
    <p>If <var title="">y<sub title="">current</sub></var> is less than <var
     title="">y<sub title="">max</sub></var>, then this is a <a
     href="#table2">table model error</a>.</p>

   <li>
    <p>While <var title="">y<sub title="">current</sub></var> is less than
     <var title="">y<sub title="">max</sub></var>, follow these steps:</p>

    <ol>
     <li>
      <p>Increase <var title="">y<sub title="">current</sub></var> by 1.</p>

     <li>
      <p>Run the <a href="#algorithm1">algorithm for growing downward-growing
       cells</a>.</p>
    </ol>

   <li>
    <p>Empty the <var title="">list of downward-growing cells</var>.</p>
  </ol>

  <p>The <dfn id=algorithm0>algorithm for processing rows</dfn>, which is
   invoked by the set of steps above for processing <code><a
   href="#tr">tr</a></code> elements, is:

  <ol>
   <li>
    <p>Increase <var title="">y<sub title="">current</sub></var> by 1.</p>
    <!-- ymax is increased below once we know cell dimensions -->

   <li>
    <p>Run the <a href="#algorithm1">algorithm for growing downward-growing
     cells</a>.</p>

   <li>
    <p>Let <var title="">x<sub title="">current</sub></var> be 1.</p>
    <!-- xmax is increased below once we know cell dimensions -->

   <li>
    <p>If the <code><a href="#tr">tr</a></code> element being processed
     contains no <code><a href="#td">td</a></code> or <code><a
     href="#th">th</a></code> elements, then abort this set of steps and
     return to the algorithm above.</p>

   <li>
    <p>Let <var title="">current cell</var> be the first <code><a
     href="#td">td</a></code> or <code><a href="#th">th</a></code> element in
     the <code><a href="#tr">tr</a></code> element being processed.</p>

   <li>
    <p><em>Cells.</em> While <var title="">x<sub title="">current</sub></var>
     is less than or equal to <var title="">x<sub title="">max</sub></var>
     and the slot with coordinate (<var title="">x<sub
     title="">current</sub></var>, <var title="">y<sub
     title="">current</sub></var>) already has a cell assigned to it,
     increase <var title="">x<sub title="">current</sub></var> by 1.</p>

   <li>
    <p>If <var title="">x<sub title="">current</sub></var> is greater than
     <var title="">x<sub title="">max</sub></var>, increase <var
     title="">x<sub title="">max</sub></var> by 1 (which will make them
     equal).</p>

   <li>
    <p>If the <var title="">current cell</var> has a <code
     title="">colspan</code> attribute, then <span title="rules for parsing
     non-negative integer values">parse that attribute's value</span>, and
     let <var title="">colspan</var> be the result.</p>

    <p>If parsing that value failed, or returned zero, or if the attribute is
     absent, then let <var title="">colspan</var> be 1, instead.</p>

   <li>
    <p>If the <var title="">current cell</var> has a <code
     title="">rowspan</code> attribute, then <span title="rules for parsing
     non-negative integer values">parse that attribute's value</span>, and
     let <var title="">rowspan</var> be the result.</p>

    <p>If parsing that value failed or if the attribute is absent, then let
     <var title="">rowspan</var> be 1, instead.</p>

   <li>
    <p>If <var title="">rowspan</var> is zero, then let <var title="">cell
     grows downward</var> be true, and set <var title="">rowspan</var> to 1.
     Otherwise, let <var title="">cell grows downward</var> be false.</p>

   <li>
    <p>If <span><var title="">x<sub
     title="">max</sub></var>&nbsp;&lt;&nbsp;<var title="">x<sub
     title="">current</sub></var>+<var title="">colspan</var>-1</span>, then
     let <var title="">x<sub title="">max</sub></var> be <var title="">x<sub
     title="">current</sub></var>+<var title="">colspan</var>-1.</p>

   <li>
    <p>If <span><var title="">y<sub
     title="">max</sub></var>&nbsp;&lt;&nbsp;<var title="">y<sub
     title="">current</sub></var>+<var title="">rowspan</var>-1</span>, then
     let <var title="">y<sub title="">max</sub></var> be <var title="">y<sub
     title="">current</sub></var>+<var title="">rowspan</var>-1.</p>

   <li>
    <p>Let the slots with coordinates (<var title="">x</var>, <var
     title="">y</var>) such that <span><var title="">x<sub
     title="">current</sub></var>&nbsp;&le;&nbsp;<var
     title="">x</var>&nbsp;&lt;&nbsp;<var title="">x<sub
     title="">current</sub></var>+<var title="">colspan</var></span> and
     <span><var title="">y<sub
     title="">current</sub></var>&nbsp;&le;&nbsp;<var
     title="">y</var>&nbsp;&lt;&nbsp;<var title="">y<sub
     title="">current</sub></var>+<var title="">rowspan</var></span> be
     covered by a new <a href="#cell" title=concept-cell>cell</a> <var
     title="">c</var>, anchored at (<var title="">x<sub
     title="">current</sub></var>, <var title="">y<sub
     title="">current</sub></var>), which has width <var
     title="">colspan</var> and height <var title="">rowspan</var>,
     corresponding to the <var title="">current cell</var> element.</p>

    <p>If the <var title="">current cell</var> element is a <code><a
     href="#th">th</a></code> element, let this new cell <var
     title="">c</var> be a header cell; otherwise, let it be a data cell. To
     establish what header cells apply to a data cell, use the <a
     href="#algorithm2">algorithm for assigning header cells to data
     cells</a> described in the next section.</p>

    <p>If any of the slots involved already had a <a href="#cell"
     title=concept-cell>cell</a> covering them, then this is a <a
     href="#table2">table model error</a>. Those slots now have two cells
     overlapping.</p>

   <li>
    <p>If <var title="">cell grows downward</var> is true, then add the tuple
     {<var title="">c</var>, <var title="">x<sub
     title="">current</sub></var>, <var title="">colspan</var>} to the <var
     title="">list of downward-growing cells</var>.</p>

   <li>
    <p>Increase <var title="">x<sub title="">current</sub></var> by <var
     title="">colspan</var>.</p>

   <li>
    <p>If <var title="">current cell</var> is the last <code><a
     href="#td">td</a></code> or <code><a href="#th">th</a></code> element in
     the <code><a href="#tr">tr</a></code> element being processed, then
     abort this set of steps and return to the algorithm above.</p>

   <li>
    <p>Let <var title="">current cell</var> be the next <code><a
     href="#td">td</a></code> or <code><a href="#th">th</a></code> element in
     the <code><a href="#tr">tr</a></code> element being processed.</p>

   <li>
    <p>Return to step 5 (cells).</p>
  </ol>

  <p>The <dfn id=algorithm1>algorithm for growing downward-growing
   cells</dfn>, used when adding a new row, is as follows:

  <ol>
   <li>
    <p>If the <var title="">list of downward-growing cells</var> is empty, do
     nothing. Abort these steps; return to the step that invoked this
     algorithm.</p>

   <li>
    <p>Otherwise, if <var title="">y<sub title="">max</sub></var> is less
     than <var title="">y<sub title="">current</sub></var>, then increase
     <var title="">y<sub title="">max</sub></var> by 1 (this will make it
     equal to <var title="">y<sub title="">current</sub></var>).</p>

   <li>
    <p>For each {<var title="">cell</var>, <var title="">cell<sub
     title="">x</sub></var>, <var title="">width</var>} tuple in the <var
     title="">list of downward-growing cells</var>, extend the <a
     href="#cell" title=concept-cell>cell</a> <var title="">cell</var> so
     that it also covers the slots with coordinates (<var title="">x</var>,
     <var title="">y<sub title="">current</sub></var>), where <span><var
     title="">cell<sub title="">x</sub></var>&nbsp;&le;&nbsp;<var
     title="">x</var>&nbsp;&lt;&nbsp;<var title="">cell<sub
     title="">x</sub></var>+<var title="">width</var>-1</span>.</p>
  </ol>

  <p>If, after establishing which elements correspond to which slots, there
   exists a <a href="#column" title=concept-column>column</a> in the <a
   href="#table1" title=concept-table>table</a> containing only <span
   title=concept-slot>slots</span> that do not have a <a href="#cell"
   title=concept-cell>cell</a> anchored to them, then this is a <a
   href="#table2">table model error</a>.

  <h5 id=header-and-data-cell-semantics><span class=secno>3.15.11.2.
   </span>Forming relationships between data cells and header cells</h5>

  <p>Each data cell can be assigned zero or more header cells. The <dfn
   id=algorithm2>algorithm for assigning header cells to data cells</dfn> is
   as follows.

  <p>For each header cell in the table, in <a href="#tree-order">tree
   order</a>:

  <ol>
   <li>
    <p>Let (<var title="">header<sub title="">x</sub></var>, <var
     title="">header<sub title="">y</sub></var>) be the coordinate of the
     slot to which the header cell is anchored.</p>

   <li>
    <p>Examine the <code title=attr-th-scope><a
     href="#scope0">scope</a></code> attribute of the <code><a
     href="#th">th</a></code> element corresponding to the header cell, and,
     based on its state, apply the appropriate substep:</p>

    <dl class=switch>
     <dt>If it is in the <em title=attr-th-scope-row><a
      href="#row">row</a></em> state

     <dd>
      <p>Assign the header cell to any data cells anchored at slots with
       coordinates (<var title="">data<sub title="">x</sub></var>, <var
       title="">data<sub title="">y</sub></var>) where <span><var
       title="">header<sub title="">x</sub></var>&nbsp;&lt;&nbsp;<var
       title="">data<sub title="">x</sub></var>&nbsp;&le;&nbsp;<var
       title="">x<sub title="">max</sub></var></span> and <span><var
       title="">data<sub title="">y</sub></var>&nbsp;=&nbsp;<var
       title="">header<sub title="">y</sub></var></span>.</p>

     <dt>If it is in the <em title=attr-th-scope-col><a
      href="#col0">column</a></em> state

     <dd>
      <p>Assign the header cell to any data cells anchored at slots with
       coordinates (<var title="">data<sub title="">x</sub></var>, <var
       title="">data<sub title="">y</sub></var>) where <span><var
       title="">data<sub title="">x</sub></var>&nbsp;=&nbsp;<var
       title="">header<sub title="">x</sub></var></span> and <span><var
       title="">header<sub title="">y</sub></var>&nbsp;&lt;&nbsp;<var
       title="">data<sub title="">y</sub></var>&nbsp;&le;&nbsp;<var
       title="">y<sub title="">max</sub></var></span>.</p>

     <dt>If it is in the <em title=attr-th-scope-rowgroup><a
      href="#rowgroup">row group</a></em> state

     <dd>
      <p>If the header cell is not in a <a href="#row-group"
       title=concept-row-group>row group</a>, then don't assign the header
       cell to any data cells.</p>

      <p>Otherwise, let (1, <var title="">group<sub title="">y</sub></var>)
       be the slot at which the row group is anchored, let <var
       title="">height</var> be the number of rows in the row group, and
       assign the header cell to any data cells anchored at slots with
       coordinates (<var title="">data<sub title="">x</sub></var>, <var
       title="">data<sub title="">y</sub></var>) where <span><var
       title="">header<sub title="">x</sub></var>&nbsp;&le;&nbsp;<var
       title="">data<sub title="">x</sub></var>&nbsp;&le;&nbsp;<var
       title="">x<sub title="">max</sub></var></span> and <span><var
       title="">header<sub title="">y</sub></var>&nbsp;&le;&nbsp;<var
       title="">data<sub title="">y</sub></var>&nbsp;&lt;&nbsp;<var
       title="">group<sub title="">y</sub></var>+<var
       title="">height</var></span>.</p>

     <dt>If it is in the <em title=attr-th-scope-colgroup><a
      href="#colgroup0">column group</a></em> state

     <dd>
      <p>If the header cell is not in a <a href="#column0"
       title=concept-column-group>column group</a>, then don't assign the
       header cell to any data cells.</p>

      <p>Otherwise, let (<var title="">group<sub title="">x</sub></var>, 1)
       be the slot at which the column group is anchored, let <var
       title="">width</var> be the number of columns in the column group, and
       assign the header cell to any data cells anchored at slots with
       coordinates (<var title="">data<sub title="">x</sub></var>, <var
       title="">data<sub title="">y</sub></var>) where <span><var
       title="">header<sub title="">x</sub></var>&nbsp;&le;&nbsp;<var
       title="">data<sub title="">x</sub></var>&nbsp;&lt;&nbsp;<var
       title="">group<sub title="">x</sub></var>+<var
       title="">width</var></span> and <span><var title="">header<sub
       title="">y</sub></var>&nbsp;&le;&nbsp;<var title="">data<sub
       title="">y</sub></var>&nbsp;&le;&nbsp;<var title="">y<sub
       title="">max</sub></var></span>.</p>

     <dt>Otherwise, it is in the <em title="">auto</em> state

     <dd>
      <p>If the header cell is not in the first row of the table, or not in
       the first cell of a row, then don't assign the header cell to any data
       cells.</p>

      <p>Otherwise, if the header cell is in the first row of the table,
       assign the header cell to any data cells anchored at slots with
       coordinates (<var title="">data<sub title="">x</sub></var>, <var
       title="">data<sub title="">y</sub></var>) where <span><var
       title="">data<sub title="">x</sub></var>&nbsp;=&nbsp;<var
       title="">header<sub title="">x</sub></var></span> and <span><var
       title="">header<sub title="">y</sub></var>&nbsp;&lt;&nbsp;<var
       title="">data<sub title="">y</sub></var>&nbsp;&le;&nbsp;<var
       title="">y<sub title="">max</sub></var></span>.</p>

      <p>Otherwise, the header cell is in the first column of the table;
       assign the header cell to any data cells anchored at slots with
       coordinates (<var title="">data<sub title="">x</sub></var>, <var
       title="">data<sub title="">y</sub></var>) where <span><var
       title="">header<sub title="">x</sub></var>&nbsp;&lt;&nbsp;<var
       title="">data<sub title="">x</sub></var>&nbsp;&le;&nbsp;<var
       title="">x<sub title="">max</sub></var></span> and <span><var
       title="">data<sub title="">y</sub></var>&nbsp;=&nbsp;<var
       title="">header<sub title="">y</sub></var></span>.</p>
    </dl>
  </ol>

  <h3 id=forms><span class=secno>3.16. </span>Forms</h3>
  <!-- XXX everything in WF2 -->

  <p class=big-issue>This section will contain definitions of the
   <code>form</code> element and so forth.

  <p class=big-issue>This section will be a rewrite of the HTML4 Forms and
   Web Forms 2.0 specifications, with hopefully no normative changes.</p>
  <!-- From HTML4: BUTTON FIELDSET FORM INPUT LABEL OPTGROUP OPTION
  SELECT TEXTAREA -->

  <h4 id=the-form><span class=secno>3.16.1. </span>The <code>form</code>
   element</h4>

  <h4 id=the-fieldset><span class=secno>3.16.2. </span>The
   <code>fieldset</code> element</h4>

  <h4 id=the-input><span class=secno>3.16.3. </span>The <code>input</code>
   element</h4>

  <h4 id=the-button><span class=secno>3.16.4. </span>The <code>button</code>
   element</h4>

  <h4 id=the-label><span class=secno>3.16.5. </span>The <code>label</code>
   element</h4>

  <h4 id=the-select><span class=secno>3.16.6. </span>The <code>select</code>
   element</h4>

  <h4 id=the-datalist><span class=secno>3.16.7. </span>The
   <code>datalist</code> element</h4>

  <h4 id=the-optgroup><span class=secno>3.16.8. </span>The
   <code>optgroup</code> element</h4>

  <h4 id=the-option><span class=secno>3.16.9. </span>The <code>option</code>
   element</h4>

  <h4 id=the-textarea><span class=secno>3.16.10. </span>The
   <code>textarea</code> element</h4>

  <h4 id=the-output><span class=secno>3.16.11. </span>The <code>output</code>
   element</h4>

  <h4 id=processing0><span class=secno>3.16.12. </span>Processing model</h4>

  <p class=big-issue>See <a
   href="http://www.whatwg.org/specs/web-forms/current-work/#extend-form-controls">WF2</a>
   for now

  <h5 id=form-submission><span class=secno>3.16.12.1. </span>Form submission</h5>

  <p class=big-issue>See <a
   href="http://www.whatwg.org/specs/web-forms/current-work/#form-submission">WF2</a>
   for now

  <h3 id=scripting0><span class=secno>3.17. </span>Scripting</h3>

  <h4 id=script><span class=secno>3.17.1. </span>The <dfn
   id=script0><code>script</code></dfn> element</h4>

  <p><a href="#block-level0" title="block-level elements">Block-level
   element</a>, <a href="#strictly">strictly inline-level content</a>, and <a
   href="#metadata" title="metadata elements">metadata element</a>.

  <dl class=element>
   <dt>Contexts in which this element may be used:

   <dd>In a <code><a href="#head">head</a></code> element.

   <dd>Where <a href="#block-level0">block-level elements</a> are expected.

   <dd>Where <a href="#inline-level0">inline-level content</a> is expected.

   <dt>Content model:

   <dd>If there is no <code title=attr-script-src><a
    href="#src9">src</a></code> attribute, depends on the value of the <code
    title=attr-script-type><a href="#type11">type</a></code> attribute.

   <dd>If there <em>is</em> a <code title=attr-script-src><a
    href="#src9">src</a></code> attribute, the element must be empty.

   <dt>Element-specific attributes:

   <dd><code title=attr-script-src><a href="#src9">src</a></code>

   <dd><code title=attr-script-defer><a href="#defer">defer</a></code>

   <dd><code title=attr-script-async><a href="#async">async</a></code>

   <dd><code title=attr-script-type><a href="#type11">type</a></code>

   <dt>DOM interface:

   <dd>
    <pre
     class=idl>interface <dfn id=htmlscriptelement>HTMLScriptElement</dfn> : <a href="#htmlelement">HTMLElement</a> {
           attribute DOMString <code title=dom-script-src><a href="#src10">src</a></code>;
           attribute boolean <code title=dom-script-defer><a href="#defer0">defer</a></code>;
           attribute boolean <code title=dom-script-async><a href="#async0">async</a></code>;
           attribute DOMString <code title=dom-script-type><a href="#type12">type</a></code>;
           attribute DOMString <code title=dom-script-text><a href="#text0">text</a></code>;
};</pre>
  </dl>

  <p>The <code><a href="#script0">script</a></code> element allows authors to
   include dynamic script in their documents.

  <p>When the <dfn id=src9 title=attr-script-src><code>src</code></dfn>
   attribute is set, the <code><a href="#script0">script</a></code> element
   refers to an external file. The value of the attribute must be a URI (or
   IRI).

  <p>If the <code title=attr-script-src><a href="#src9">src</a></code>
   attribute is not set, then the script is given by the contents of the
   element.

  <p>The language of the script may be given by the <dfn id=type11
   title=attr-script-type><code>type</code></dfn> attribute. If the attribute
   is present, its value must be a valid MIME type, optionally with
   parameters. <a href="#refsRFC2046">[RFC2046]</a>

  <p>The <dfn id=defer title=attr-script-defer><code>defer</code></dfn> and
   <dfn id=async title=attr-script-async><code>async</code></dfn> attributes
   are <a href="#boolean0" title="boolean attribute">boolean attributes</a>
   that indicate how the script should be executed.

  <p>There are three possible modes that can be selected using these
   attributes. If the <code title=attr-script-defer><a
   href="#defer">defer</a></code> attribute is present, then the script is
   executed when the page has finished parsing. If the <code
   title=attr-script-defer><a href="#defer">defer</a></code> attribute is not
   present but the <code title=attr-script-async><a
   href="#async">async</a></code> attribute is present, then the script will
   be executed asynchronously, as soon as it is available. If neither
   attribute is present, then the script is downloaded and executed
   immediately, before the user agent continues parsing the page. The exact
   processing details for these attributes is described below.

  <p>The <code title=attr-script-async><a href="#async">async</a></code>
   attribute must not be specified if the <code title=attr-script-defer><a
   href="#defer">defer</a></code> attribute is specified.

  <p>Changing the <code title=attr-script-src><a href="#src9">src</a></code>,
   <code title=attr-script-type><a href="#type11">type</a></code>, <code
   title=attr-script-defer><a href="#defer">defer</a></code> and <code
   title=attr-script-async><a href="#async">async</a></code> attributes
   dynamically has no direct effect; these attribute are only used at
   specific times described below (namely, when the element is inserted into
   the document).

  <p><code><a href="#script0">script</a></code> elements have three
   associated pieces of metadata. The first is a flag indicating whether or
   not the script block has been <dfn id=already>"already executed"</dfn>.
   Initially, <code><a href="#script0">script</a></code> elements must have
   this flag unset (script blocks, when created, are not "already executed").
   When a <code><a href="#script0">script</a></code> element is cloned, the
   "already executed" flag, if set, must be propagated to the clone when it
   is created. The second is a flag indicating whether the element was <dfn
   id=parser-inserted>"parser-inserted"</dfn>. This flag is set by the <a
   href="#html-0">HTML parser</a> and is used to handle <code
   title=dom-document-write-HTML><a
   href="#document.write0">document.write()</a></code> calls. The third piece
   of metadata is <dfn id=the-scripts><var>the script's type</var></dfn>. It
   is determined when the script is run, based on the attributes on the
   element at that time.

  <p><dfn id=running0 title="running a script">Running a script</dfn>: when a
   script block is <span>inserted into a document</span>, the user agent must
   act as follows:

  <ol>
   <li>
    <p>If the <code><a href="#script0">script</a></code> element has a <code
     title=attr-script-type><a href="#type11">type</a></code> attribute but
     its value is the empty string, or if the <code><a
     href="#script0">script</a></code> element has no <code
     title=attr-script-type><a href="#type11">type</a></code> attribute but
     it has a <code title=attr-script-language>language</code> attribute, and
     <em>that</em> attribute's value is the empty string, let <var><a
     href="#the-scripts">the script's type</a></var> for this <code><a
     href="#script0">script</a></code> element be "<code
     title="">text/javascript</code>".</p>

    <p>Otherwise, if the <code><a href="#script0">script</a></code> element
     has a <code title=attr-script-type><a href="#type11">type</a></code>
     attribute, let <var><a href="#the-scripts">the script's type</a></var>
     for this <code><a href="#script0">script</a></code> element be the value
     of that attribute.</p>

    <p>Otherwise, if the element has a <code
     title=attr-script-language>language</code> attribute, let <var><a
     href="#the-scripts">the script's type</a></var> for this <code><a
     href="#script0">script</a></code> element be the concatenation of the
     string "<code title="">text/</code>" followed by the value of the <code
     title=attr-script-language>language</code> attribute.</p>

   <li>
    <p>If <a href="#scripting1">scripting is disabled</a>, or if the
     <code>Document</code> has <code title=dom-document-designMode><a
     href="#designMode">designMode</a></code> enabled, or if the user agent
     does not <a href="#support">support the scripting language</a> given by
     <var><a href="#the-scripts">the script's type</a></var> for this
     <code><a href="#script0">script</a></code> element, or if the <code><a
     href="#script0">script</a></code> element has its <a
     href="#already">"already executed"</a> flag set, then the user agent
     must abort these steps at this point. The script is not executed.</p>

   <li>
    <p>The user agent must set the element's <a href="#already">"already
     executed"</a> flag.</p>

   <li>
    <p>If the element has a <code title=attr-script-src><a
     href="#src9">src</a></code> attribute, then a load for the specified
     content must be started.</p>

    <p class=note>Later, once the load has completed, the user agent will
     have to complete <a href="#when-a" title="when a script completes
     loading">the steps described below</a>.</p>

    <p>For performance reasons, user agents may start loading the script as
     soon as the attribute is set, instead, in the hope that the element will
     be inserted into the document. Either way, once the element is inserted
     into the document, the load must have started. If the UA performs such
     prefetching, but the element is never inserted in the document, or the
     <code title=attr-script-src><a href="#src9">src</a></code> attribute is
     dynamically changed, then the user agent will not execute the script,
     and the load will have been effectively wasted.</p>

   <li>
    <p>Then, the first of the following options that describes the situation
     must be followed:</p>

    <dl class=switch>
     <dt>If the document is still being parsed, and the element has a <code
      title=attr-script-defer><a href="#defer">defer</a></code> attribute

     <dd>The element must be added to the end of the <a href="#list-of">list
      of scripts that will execute when the document has finished
      parsing</a>. The user agent must begin <a href="#when-a" title="when a
      script completes loading">the next set of steps</a> when the script is
      ready. <span class=big-issue>This isn't compatible with IE for inline
      deferred scripts, but then what IE does is pretty hard to pin down
      exactly. Do we want to keep this like it is? Be more compatible?</span>
      <!--XXX  
     http://www.websiteoptimization.com/speed/tweak/defer/test/
     internal deferred scripts execute before any external scripts execute, or before the LOAD if there are none
     external deferred scripts execute before the LOAD
     -->
      

     <dt>If the element has an <code title=attr-script-async><a
      href="#async">async</a></code> attribute and a <code
      title=attr-script-src><a href="#src9">src</a></code> attribute

     <dd>The element must be added to the end of the <a href="#list-of0">list
      of scripts that will execute asynchronously</a>. The user agent must
      jump to <a href="#when-a" title="when a script completes loading">the
      next set of steps</a> once the script is ready.

     <dt>If the element has an <code title=attr-script-async><a
      href="#async">async</a></code> attribute but no <code
      title=attr-script-src><a href="#src9">src</a></code> attribute, and the
      <a href="#list-of0">list of scripts that will execute
      asynchronously</a> is not empty

     <dd>The element must be added to the end of the <a href="#list-of0">list
      of scripts that will execute asynchronously</a>.

     <dt>If the element has a <code title=attr-script-src><a
      href="#src9">src</a></code> attribute and has been flagged as <a
      href="#parser-inserted">"parser-inserted"</a>

     <dd>The element is <a href="#the-script">the script that will execute as
      soon as the parser resumes</a>. (There can only be one such script at a
      time.)

     <dt>If the element has a <code title=attr-script-src><a
      href="#src9">src</a></code> attribute

     <dd>The element must be added to the end of the <a href="#list-of1">list
      of scripts that will execute as soon as possible</a>. The user agent
      must jump to <a href="#when-a" title="when a script completes
      loading">the next set of steps</a> when the script is ready.

     <dt>Otherwise

     <dd>The user agent must immediately <a href="#executing0"
      title="executing a script block">execute the script</a>, even if other
      scripts are already executing.
    </dl>
  </ol>

  <p><dfn id=when-a title="when a script completes loading">When a script
   completes loading</dfn>: If a script whose element was added to one of the
   lists mentioned above completes loading while the document is still being
   parsed, then the parser handles it. Otherwise, when a script completes
   loading, the UA must follow the following steps as soon as as any other
   scripts that may be executing have finished executing:

  <dl class=switch>
   <dt>If the script's element was added to the <dfn id=list-of>list of
    scripts that will execute when the document has finished parsing</dfn>:

   <dd>
    <ol>
     <li>
      <p>If the script's element is not the first element in the list, then
       do nothing yet. Stop going through these steps.</p>

     <li>
      <p>Otherwise, <a href="#executing0" title="executing a script
       block">execute the script</a> (that is, the script associated with the
       first element in the list).</p>

     <li>
      <p>Remove the script's element from the list (i.e. shift out the first
       entry in the list).</p>

     <li>
      <p>If there are any more entries in the list, and if the script
       associated with the element that is now the first in the list is
       already loaded, then jump back to step two to execute it.</p>
    </ol>

   <dt>If the script's element was added to the <dfn id=list-of0>list of
    scripts that will execute asynchronously</dfn>:

   <dd>
    <ol>
     <li>
      <p>If the script is not the first element in the list, then do nothing
       yet. Stop going through these steps.</p>

     <li>
      <p><a href="#executing0" title="executing a script block">Execute the
       script</a> (the script associated with the first element in the list).</p>

     <li>
      <p>Remove the script's element from the list (i.e. shift out the first
       entry in the list).</p>

     <li>
      <p>If there are any more scripts in the list, and the element now at
       the head of the list had no <code title=attr-script-src><a
       href="#src9">src</a></code> attribute when it was added to the list,
       or had one, but its associated script has finished loading, then jump
       back to step two to execute the script associated with this element.</p>
    </ol>

   <dt>If the script's element was added to the <dfn id=list-of1>list of
    scripts that will execute as soon as possible</dfn>:

   <dd>
    <ol>
     <li>
      <p><a href="#executing0" title="executing a script block">Execute the
       script</a>.</p>

     <li>
      <p>Remove the script's element from the list.</p>
    </ol>

   <dt>If the script is <dfn id=the-script>the script that will execute as
    soon as the parser resumes</dfn>:

   <dd>
    <p>The script will be handled <a href="#scriptTagParserResumes">when the
     parser resumes</a> (amazingly enough).</p>
  </dl>

  <p>The download of an external script must <a href="#delays">delay the
   <code title=event-load>load</code> event</a>.

  <p><dfn id=executing0 title="executing a script block">Executing a script
   block</dfn>: If the load resulted in an error (for example a DNS error, or
   an HTTP 404 error), then executing the script must just consist of <a
   href="#firing5" title="fire an error event">firing an <code
   title=event-error>error</code> event</a> at the element.

  <p>If the load was successful, then first the user agent must <a
   href="#firing4">fire a <code title=event-load>load</code> event</a> at the
   element, and then, if <a href="#scripting2">scripting is enabled</a>, and
   the <code>Document</code> does not have <code
   title=dom-document-designMode><a href="#designMode">designMode</a></code>
   enabled, and the <code>Document</code> is the <a href="#active">active
   document</a> in its <a href="#browsing0">browsing context</a>, the user
   agent must execute the script:

  <p>If the script is from an external file, then that file must be used as
   the file to execute.

  <p>If the script is inline, then, for scripting languages that consist of
   pure text, user agents must use the value of the DOM <code
   title=dom-script-text><a href="#text0">text</a></code> attribute (defined
   below) as the script to execute, and for XML-based scripting languages,
   user agents must use all the child nodes of the <code><a
   href="#script0">script</a></code> element as the script to execute.

  <p>In any case, the user agent must execute the script according to the
   semantics defined by the language associated with <var><a
   href="#the-scripts">the script's type</a></var> (see the <a
   href="#scriptingLanguages">scripting languages</a> section below).

  <p>Scripts must be executed in the scope of the <a
   href="#browsing0">browsing context</a> of the element's
   <code>Document</code>.

  <p class=note>The element's attributes' values might have changed between
   when the element was inserted into the document and when the script has
   finished loading, as may its other attributes; similarly, the element
   itself might have been taken back out of the DOM, or had other changes
   made. These changes do not in any way affect the above steps; only the
   values of the attributes at the time the <code><a
   href="#script0">script</a></code> element is first inserted into the
   document matter.

  <p>The DOM attributes <dfn id=src10
   title=dom-script-src><code>src</code></dfn>, <dfn id=type12
   title=dom-script-type><code>type</code></dfn>, <dfn id=defer0
   title=dom-script-defer><code>defer</code></dfn>, <dfn id=async0
   title=dom-script-async><code>async</code></dfn>, each must <a
   href="#reflect">reflect</a> the respective content attributes of the same
   name.

  <p>The DOM attribute <dfn id=text0
   title=dom-script-text><code>text</code></dfn> must return a concatenation
   of the contents of all the <a href="#text-node" title="text node">text
   nodes</a> that are direct children of the <code><a
   href="#script0">script</a></code> element (ignoring any other nodes such
   as comments or elements), in tree order. On setting, it must act the same
   way as the <code><a href="#textcontent">textContent</a></code> DOM
   attribute.

  <h5 id=scriptingLanguages><span class=secno>3.17.1.1. </span>Scripting
   languages</h5>

  <p>A user agent is said to <dfn id=support>support the scripting
   language</dfn> if <var><a href="#the-scripts">the script's type</a></var>
   matches the MIME type of a scripting language that the user agent
   implements.

  <p>The following lists some MIME types and the languages to which they
   refer:

  <dl>
   <dt><code>text/javascript</code>

   <dd>ECMAScript. <a href="#refsECMA262">[ECMA262]</a>

   <dt><code>text/javascript;e4x=1</code>

   <dd>ECMAScript with ECMAScript for XML. <a
    href="#refsECMA357">[ECMA357]</a>
  </dl>

  <p>User agents may support other MIME types and other languages.

  <p>When examining types to determine if they support the language, user
   agents must not ignore unknown MIME parameters &mdash; types with unknown
   parameters must be assumed to be unsupported.</p>
  <!--
   XXX we should reference #refsRFC4329 http://www.ietf.org/rfc/rfc4329
  -->

  <h4 id=the-noscript><span class=secno>3.17.2. </span>The <dfn
   id=noscript><code>noscript</code></dfn> element</h4>

  <p>When <a href="#scripting1">scripting is disabled</a>: <a
   href="#transparent0">transparent</a> <a href="#block-level0"
   title="block-level elements">block-level element</a>, and <a
   href="#transparent0">transparent</a> <a href="#strictly">strictly
   inline-level content</a>.

  <p>When <a href="#scripting2">scripting is enabled</a>: <a
   href="#block-level0" title="block-level elements">block-level element</a>,
   and <a href="#strictly">strictly inline-level content</a>.

  <dl class=element>
   <dt>Contexts in which this element may be used:

   <dd>In a <code><a href="#head">head</a></code> element of an <a
    href="#html-" title=">HTML documents">HTML document</a>, if there are no
    ancestor <code><a href="#noscript">noscript</a></code> elements.

   <dd>Where <a href="#block-level0">block-level elements</a> are expected in
    <a href="#html-">HTML documents</a>, if there are no ancestor <code><a
    href="#noscript">noscript</a></code> elements.

   <dd>Where <a href="#inline-level0">inline-level content</a> is expected in
    <a href="#html-">HTML documents</a>, if there are no ancestor <code><a
    href="#noscript">noscript</a></code> elements.

   <dt>Content model:

   <dd>When <a href="#scripting1">scripting is disabled</a>: <a
    href="#transparent0">transparent</a>, but there must be no <code><a
    href="#noscript">noscript</a></code> element descendants.

   <dd>When <a href="#scripting2">scripting is enabled</a>: Text that
    conforms to the requirements given in the prose.

   <dt>Element-specific attributes:

   <dd>None.

   <dt>DOM interface:

   <dd>No difference from <code><a
    href="#htmlelement">HTMLElement</a></code>.
  </dl>

  <p>The <code><a href="#noscript">noscript</a></code> element does not
   represent anything. It is used to present different markup to user agents
   that support scripting and those that don't support scripting, by
   affecting how the document is parsed.

  <p>The <code><a href="#noscript">noscript</a></code> element must not be
   used in <a href="#xml-documents">XML documents</a>.

  <p>When used in <a href="#html-">HTML documents</a>, the allowed content
   model depends on whether scripting is enabled or not.

  <p>If <a href="#scripting1">scripting is disabled</a>, then the content
   model of a <code><a href="#noscript">noscript</a></code> element is <a
   href="#transparent0">transparent</a>, with the additional restriction that
   a <code><a href="#noscript">noscript</a></code> element must not have a
   <code><a href="#noscript">noscript</a></code> element as an ancestor (that
   is, <code><a href="#noscript">noscript</a></code> can't be nested).

  <p>If <a href="#scripting2">scripting is enabled</a>, then the content
   model of a <code><a href="#noscript">noscript</a></code> element is text,
   except that the text must be such that running the following algorithm
   results in a conforming document with no <code><a
   href="#noscript">noscript</a></code> elements and no <code><a
   href="#script0">script</a></code> elements, and such that no step in the
   algorithm causes an <a href="#html-0">HTML parser</a> to flag a <a
   href="#parse">parse error</a>:

  <ol>
   <li>Remove every <code><a href="#script0">script</a></code> element from
    the document.

   <li>Make a list of every <code><a href="#noscript">noscript</a></code>
    element in the document. For every <code><a
    href="#noscript">noscript</a></code> element in that list, perform the
    following steps:
    <ol>
     <li>Let the <var title="">parent element</var> be the parent element of
      the <code><a href="#noscript">noscript</a></code> element.

     <li>Take all the children of the <var title="">parent element</var> that
      come before the <code><a href="#noscript">noscript</a></code> element,
      and call these elements <var title="">the before children</var>.

     <li>Take all the children of the <var title="">parent element</var> that
      come <em>after</em> the <code><a href="#noscript">noscript</a></code>
      element, and call these elements <var title="">the after
      children</var>.

     <li>Let <var title="">s</var> be the concatenation of all the <a
      href="#text-node">text node</a> children of the <code><a
      href="#noscript">noscript</a></code> element.

     <li>Set the <code title=dom-innerHTML-HTML><a
      href="#innerhtml0">innerHTML</a></code> attribute of the <var
      title="">parent element</var> to the value of <var title="">s</var>.
      (This, as a side-effect, causes the <code><a
      href="#noscript">noscript</a></code> element to be removed from the
      document.)

     <li>Insert <var title="">the before children</var> at the start of the
      <var title="">parent element</var>, preserving their original relative
      order.

     <li>Insert <var title="">the after children</var> at the end of the <var
      title="">parent element</var>, preserving their original relative
      order.
    </ol>
  </ol>

  <p>The <code><a href="#noscript">noscript</a></code> element has no other
   requirements. In particular, children of the <code><a
   href="#noscript">noscript</a></code> element are not exempt from form
   submission, scripting, and so forth, even when scripting is enabled.

  <p class=note>All these contortions are required because, for historical
   reasons, the <code><a href="#noscript">noscript</a></code> element causes
   the <a href="#html-0">HTML parser</a> to act differently based on whether
   scripting is enabled or not. The element is not allowed in XML, because in
   XML the parser is not affected by such state, and thus the element would
   not have the desired effect.

  <h4 id=the-event-source><span class=secno>3.17.3. </span>The <dfn
   id=event-source><code>event-source</code></dfn> element</h4>

  <p><a href="#block-level0" title="block-level elements">Block-level
   element</a>, <a href="#strictly">strictly inline-level content</a>, and <a
   href="#metadata" title="metadata elements">metadata element</a>.

  <dl class=element>
   <dt>Contexts in which this element may be used:

   <dd>In a <code><a href="#head">head</a></code> element.

   <dd>Where <a href="#block-level0">block-level elements</a> are expected.

   <dd>Where <a href="#inline-level0">inline-level content</a> is expected.

   <dt>Content model:

   <dd>Empty.

   <dt>Element-specific attributes:

   <dd><code title=attr-event-source-src><a href="#src11">src</a></code>

   <dt>DOM interface:

   <dd>
    <pre
     class=idl>interface <dfn id=htmleventsourceelement>HTMLEventSourceElement</dfn> : <a href="#htmlelement">HTMLElement</a> {
           attribute DOMString <a href="#src12" title=dom-event-source-src>src</a>;
};</pre>
  </dl>

  <p>The <code><a href="#event-source">event-source</a></code> element
   represents a target for events generated by a remote server.

  <p>The <dfn id=src11 title=attr-event-source-src><code>src</code></dfn>
   attribute, if specified, must give a URI (or IRI) pointing to a resource
   that uses the <code>application/x-dom-event-stream</code> format.

  <p>When the element is inserted into the document, if it has the <code
   title=attr-event-source-src><a href="#src11">src</a></code> attribute
   specified, the user agent must act as if the <code
   title=dom-remoteEventTarget-addEventSource><a
   href="#addeventsource">addEventSource()</a></code> method on the <code><a
   href="#event-source">event-source</a></code> element had been invoked with
   the URI resulting from resolving the <code title=attr-event-source-src><a
   href="#src11">src</a></code> attribute's value to an absolute URI.

  <p>While the element is in a document, if its <code
   title=attr-event-source-src><a href="#src11">src</a></code> attribute is
   mutated, the user agent must act as if first the <code
   title=dom-remoteEventTarget-removeEventSource><a
   href="#removeeventsource">removeEventSource()</a></code> method on the
   <code><a href="#event-source">event-source</a></code> element had been
   invoked with the URI resulting from resolving the old value of the
   attribute to an absolute URI, and then as if the <code
   title=dom-remoteEventTarget-addEventSource><a
   href="#addeventsource">addEventSource()</a></code> method on the element
   had been invoked with the URI resulting from resolving the <em>new</em>
   value of the <code title=attr-event-source-src><a
   href="#src11">src</a></code> attribute to an absolute URI.

  <p>When the element is removed from the document, if it has the <code
   title=attr-event-source-src><a href="#src11">src</a></code> attribute
   specified, or, when the <code title=attr-event-source-src><a
   href="#src11">src</a></code> attribute is about to be removed, the user
   agent must act as if the <code
   title=dom-remoteEventTarget-removeEventSource><a
   href="#removeeventsource">removeEventSource()</a></code> method on the
   <code><a href="#event-source">event-source</a></code> element had been
   invoked with the URI resulting from resolving the <code
   title=attr-event-source-src><a href="#src11">src</a></code> attribute's
   value to an absolute URI.

  <p>There can be more than one <code><a
   href="#event-source">event-source</a></code> element per document, but
   authors should take care to avoid opening multiple connections to the same
   server as HTTP recommends a limit to the number of simultaneous
   connections that a user agent can open per server.</p>
  <!-- XXX should we make 'load', 'error', 'abort' events fire on this
  element? -->

  <p>The <dfn id=src12 title=dom-event-source-src><code>src</code></dfn> DOM
   attribute must reflect the content attribute of the same name.

  <h3 id=interactive><span class=secno>3.18. </span>Interactive elements</h3>

  <h4 id=the-details><span class=secno>3.18.1. </span>The <dfn
   id=details><code>details</code></dfn> element</h4>

  <p><a href="#interactive1" title="interactive elements">Interactive</a>, <a
   href="#block-level0" title="block-level elements">block-level element</a>.

  <dl class=element>
   <dt>Contexts in which this element may be used:

   <dd>Where <a href="#block-level0">block-level elements</a> are expected.

   <dt>Content model:

   <dd>One <code><a href="#legend">legend</a></code> element followed by
    either one or more <a href="#block-level0">block-level elements</a> or <a
    href="#inline-level0">inline-level content</a> (but not both).

   <dt>Element-specific attributes:

   <dd><code title=attr-details-open><a href="#open0">open</a></code>

   <dt>DOM interface:

   <dd>
    <pre
     class=idl>interface <dfn id=htmldetailselement>HTMLDetailsElement</dfn> : <a href="#htmlelement">HTMLElement</a> {
  attribute boolean <a href="#open1" title=dom-details-open>open</a>;
};</pre>
  </dl>

  <p>The <code><a href="#details">details</a></code> element represents
   additional information or controls which the user can obtain on demand.

  <p>The first element child of a <code><a href="#details">details</a></code>
   element, if it is a <code><a href="#legend">legend</a></code> element,
   represents the summary of the details.

  <p>If the first element is not a <code><a href="#legend">legend</a></code>
   element, the UA should provide its own legend (e.g. "Details").

  <p>The <dfn id=open0 title=attr-details-open><code>open</code></dfn>
   content attribute is a <a href="#boolean0">boolean attribute</a>. If
   present, it indicates that the details should be shown to the user. If the
   attribute is absent, the details should not be shown.

  <p>If the attribute is removed, then the details should be hidden. If the
   attribute is added, the details should be shown.

  <p>The user should be able to request that the details be shown or hidden.

  <p>The <dfn id=open1 title=dom-details-open><code>open</code></dfn>
   attribute must <a href="#reflect">reflect</a> the <code
   title=attr-details-open><a href="#open0">open</a></code> content
   attribute.</p>
  <!--
http://mail.gnome.org/archives/usability/2006-June/msg00015.html
http://developer.apple.com/documentation/UserExperience/Conceptual/OSXHIGuidelines/XHIGControls/chapter_18_section_7.html
https://www.google.com/base/settings
-->

  <p class=big-issue>Rendering will be described in the Rendering section in
   due course. Basically CSS :open and :closed match the element, it's a
   block-level element by default, and when it matches :closed it renders as
   if it had an XBL binding attached to it whose template was just
   <code>&lt;template>&#x25B6;&lt;content
   includes="legend:first-child"&gt;Details&lt;/content>&lt;/template></code>,
   and when it's :open it acts as if it had an XBL binding attached to it
   whose template was just <code>&lt;template>&#x25BC;&lt;content
   includes="legend:first-child"&gt;Details&lt;/content>&lt;content/>&lt;/template></code>
   or some such.

  <p class=big-issue>Clicking the legend would make it open/close (and would
   change the content attribute). Question: Do we want the content attribute
   to reflect the actual state like this? I think we do, the DOM not
   reflecting state has been a pain in the neck before. But is it
   semantically ok?

  <h4 id=datagrid><span class=secno>3.18.2. </span>The <dfn
   id=datagrid0><code>datagrid</code></dfn> element</h4>

  <p><a href="#interactive1" title="interactive elements">Interactive</a>, <a
   href="#block-level0" title="block-level elements">block-level element</a>.

  <dl class=element>
   <dt>Contexts in which this element may be used:

   <dd>Where <a href="#block-level0">block-level elements</a> are expected,
    if there are no ancestor <a href="#interactive1">interactive
    elements</a>.

   <dt>Content model:

   <dd>Either: Nothing.

   <dd>Or: One or more <a href="#block-level0">block-level elements</a>, the
    first of which is not a <code><a href="#table">table</a></code> element.

   <dd>Or: A single <code><a href="#table">table</a></code> element.

   <dd>Or: A single <code>select</code> element.

   <dd>Or: A single <code>datalist</code> element.

   <dt>Element-specific attributes:

   <dd><code title=attr-datagrid-multiple><a
    href="#multiple0">multiple</a></code>

   <dd><code title=attr-datagrid-disabled><a
    href="#disabled3">disabled</a></code>

   <dt>DOM interface:

   <dd>
    <pre
     class=idl>interface <dfn id=htmldatagridelement>HTMLDataGridElement</dfn> : <a href="#htmlelement">HTMLElement</a> {
           attribute <a href="#datagriddataprovider">DataGridDataProvider</a> <a href="#data2" title=dom-datagrid-data>data</a>;
  readonly attribute <a href="#datagridselection">DataGridSelection</a> <a href="#selection0" title=dom-datagrid-selection>selection</a>;
           attribute boolean <a href="#multiple" title=dom-datagrid-multiple>multiple</a>;
           attribute boolean <a href="#disabled2" title=dom-datagrid-disabled>disabled</a>;
  void <a href="#updateeverything" title=dom-datagrid-updateEverything>updateEverything</a>();
  void <a href="#updaterowschanged" title=dom-datagrid-updateRowsChanged>updateRowsChanged</a>(in <a href="#rowspecification">RowSpecification</a> row, in unsigned long count);
  void <a href="#updaterowsinserted" title=dom-datagrid-updateRowsInserted>updateRowsInserted</a>(in <a href="#rowspecification">RowSpecification</a> row, in unsigned long count);
  void <a href="#updaterowsremoved" title=dom-datagrid-updateRowsRemoved>updateRowsRemoved</a>(in <a href="#rowspecification">RowSpecification</a> row, in unsigned long count);
  void <a href="#updaterowchanged" title=dom-datagrid-updateRowChanged>updateRowChanged</a>(in <a href="#rowspecification">RowSpecification</a> row);
  void <a href="#updatecolumnchanged" title=dom-datagrid-updateColumnChanged>updateColumnChanged</a>(in unsigned long column);
  void <a href="#updatecellchanged" title=dom-datagrid-updateCellChanged>updateCellChanged</a>(in <a href="#rowspecification">RowSpecification</a> row, in unsigned long column);
};</pre>
  </dl>

  <p class=big-issue>One possible thing to be added is a way to detect when a
   row/selection has been deleted, activated, etc, by the user (delete key,
   enter key, etc).</p>
  <!-- XXXPA -->

  <p class=big-issue>This element is defined as interactive, which means it
   can't contain other interactive elements, despite the fact that we expect
   it to work with other interactive elements e.g. checkboxes and input
   fields. It should be called something like a Leaf Interactive Element or
   something, which counts for ancestors looking in and not descendants
   looking out.

  <p>The <code><a href="#datagrid0">datagrid</a></code> element represents an
   interactive representation of tree, list, or tabular data.

  <p>The data being presented can come either from the content, as elements
   given as children of the <code><a href="#datagrid0">datagrid</a></code>
   element, or from a scripted data provider given by the <code
   title=dom-datagrid-data><a href="#data2">data</a></code> DOM attribute.

  <p>The <code title=attr-datagrid-multiple><a
   href="#multiple0">multiple</a></code> and <code
   title=attr-datagrid-disabled><a href="#disabled3">disabled</a></code>
   attributes are <a href="#boolean0" title="boolean attribute">boolean
   attributes</a>. Their effects are described in the processing model
   sections below.

  <p>The <dfn id=multiple
   title=dom-datagrid-multiple><code>multiple</code></dfn> and <dfn
   id=disabled2 title=dom-datagrid-disabled><code>disabled</code></dfn> DOM
   attributes must <a href="#reflect">reflect</a> the <code
   title=attr-datagrid-multiple><a href="#multiple0">multiple</a></code> and
   <code title=attr-datagrid-disabled><a
   href="#disabled3">disabled</a></code> content attributes respectively.

  <h5 id=the-datagrid><span class=secno>3.18.2.1. </span>The <code><a
   href="#datagrid0">datagrid</a></code> data model</h5>

  <p><em>This section is non-normative.</em>

  <p>In the <code><a href="#datagrid0">datagrid</a></code> data model, data
   is structured as a set of rows representing a tree, each row being split
   into a number of columns. The columns are always present in the data
   model, although individual columns may be hidden in the presentation.

  <p>Each row can have child rows. Child rows may be hidden or shown, by
   closing or opening (respectively) the parent row.

  <p>Rows are referred to by the path along the tree that one would take to
   reach the row, using zero-based indices. Thus, the first row of a list is
   row "0", the second row is row "1"; the first child row of the first row
   is row "0,0", the second child row of the first row is row "0,1"; the
   fourth child of the seventh child of the third child of the tenth row is
   "9,2,6,3", etc.

  <p>The columns can have captions. Those captions are not considered a row
   in their own right, they are obtained separately.

  <p>Selection of data in a <code><a href="#datagrid0">datagrid</a></code>
   operates at the row level. If the <code title=attr-datagrid-multiple><a
   href="#multiple0">multiple</a></code> attribute is present, multiple rows
   can be selected at once, otherwise the user can only select one row at a
   time.

  <p>The <code><a href="#datagrid0">datagrid</a></code> element can be
   disabled entirely by setting the <code title=attr-datagrid-disabled><a
   href="#disabled3">disabled</a></code> attribute.</p>
  <!--XXXDND
  <p class="big-issue">selection draggable [normative definitions are
  in the interactive part below]</p>
-->

  <p>Columns, rows, and cells can each have specific flags, known as classes,
   applied to them by the data provider. These classes <a
   href="#datagridClassSummary">affect the functionality</a> of the <code><a
   href="#datagrid0">datagrid</a></code> element, and are also <a
   href="#datagridPseudos">passed to the style system</a>. They are similar
   in concept to the <code title=attr-class><a href="#class">class</a></code>
   attribute, except that they are not specified on elements but are given by
   scripted data providers.</p>
  <!-- XXX check xrefs -->

  <h5 id=how-rows><span class=secno>3.18.2.2. </span>How rows are identified</h5>

  <p>The chains of numbers that give a row's path, or identifier, are
   represented by objects that implement the <a
   href="#rowspecification">RowSpecification</a> interface.

  <pre class=idl>interface <dfn id=rowspecification>RowSpecification</dfn> {
  // binding-specific interface
};</pre>

  <p>In ECMAScript, two classes of objects are said to implement this
   interface: Numbers representing non-negative integers, and homogeneous
   arrays of Numbers representing non-negative integers. Thus,
   <code>[1,0,9]</code> is a <a
   href="#rowspecification">RowSpecification</a>, as is <code>1</code> on its
   own. However, <code>[1,0.2,9]</code> is not a <a
   href="#rowspecification">RowSpecification</a> object, since its second
   value is not an integer.

  <p>User agents must always represent <code><a
   href="#rowspecification">RowSpecification</a></code>s in ECMAScript by
   using arrays, even if the path only has one number.

  <p>The root of the tree is represented by the empty path; in ECMAScript,
   this is the empty array (<code>[]</code>). Only the <code
   title=dom-provider-getRowCount><a
   href="#getrowcount">getRowCount()</a></code> and <code
   title=dom-provider-getChildAtPosition><a
   href="#getchildatposition">GetChildAtPosition()</a></code> methods ever
   get called with the empty path.

  <h5 id=the-data><span class=secno>3.18.2.3. </span>The data provider
   interface</h5>

  <p><em>The conformance criteria in this section apply to any implementation
   of the <code><a
   href="#datagriddataprovider">DataGridDataProvider</a></code>, including
   (and most commonly) the content author's implementation(s).</em>

  <pre class=idl>// To be implemented by Web authors as a JS object
interface <dfn id=datagriddataprovider>DataGridDataProvider</dfn> {
  void <a href="#initialize" title=dom-provider-initialize>initialize</a>(in HTMLDataGridElement datagrid);
  unsigned long <a href="#getrowcount" title=dom-provider-getRowCount>getRowCount</a>(in <a href="#rowspecification">RowSpecification</a> row);
  unsigned long <a href="#getchildatposition" title=dom-provider-getChildAtPosition>getChildAtPosition</a>(in <a href="#rowspecification">RowSpecification</a> parentRow, in unsigned long position);
  unsigned long <a href="#getcolumncount" title=dom-provider-getColumnCount>getColumnCount</a>();
  DOMString <a href="#getcaptiontext" title=dom-provider-getCaptionText>getCaptionText</a>(in unsigned long column);
  void <a href="#getcaptionclasses" title=dom-provider-getCaptionClasses>getCaptionClasses</a>(in unsigned long column, in DOMTokenList classes);
  DOMString <a href="#getrowimage" title=dom-provider-getRowImage>getRowImage</a>(in <a href="#rowspecification">RowSpecification</a> row);
  <a href="#htmlmenuelement">HTMLMenuElement</a> <a href="#getrowmenu" title=dom-provider-getRowMenu>getRowMenu</a>(in <a href="#rowspecification">RowSpecification</a> row);
  void <a href="#getrowclasses" title=dom-provider-getRowClasses>getRowClasses</a>(in <a href="#rowspecification">RowSpecification</a> row, in DOMTokenList classes);
  DOMString <a href="#getcelldata" title=dom-provider-getCellData>getCellData</a>(in <a href="#rowspecification">RowSpecification</a> row, in unsigned long column);
  void <a href="#getcellclasses" title=dom-provider-getCellClasses>getCellClasses</a>(in <a href="#rowspecification">RowSpecification</a> row, in unsigned long column, in DOMTokenList classes);
<!--XXXDND
  boolean <span title="dom-provider-canDrop">canDrop</span>(in <span>RowSpecification</span> row, in <span>RowSpecification</span> position, data);
  boolean <span title="dom-provider-dropped">dropped</span>(in <span>RowSpecification</span> row, in <span>RowSpecification</span> position, data);
-->  void <a href="#togglecolumnsortstate" title=dom-provider-toggleColumnSortState>toggleColumnSortState</a>(in unsigned long column);
  void <a href="#setcellcheckedstate" title=dom-provider-setCellCheckedState>setCellCheckedState</a>(in <a href="#rowspecification">RowSpecification</a> row, in unsigned long column, in long state);
  void <a href="#cyclecell" title=dom-provider-cycleCell>cycleCell</a>(in <a href="#rowspecification">RowSpecification</a> row, in unsigned long column);
  void <a href="#editcell" title=dom-provider-editCell>editCell</a>(in <a href="#rowspecification">RowSpecification</a> row, in unsigned long column, in DOMString data);
<!--XXXPA
  void <span title="dom-provider-performAction">performAction</span>(in DOMString action); // required if .performAction() is ever invoked on the datagrid
  void <span title="dom-provider-performActionOnRow">performActionOnRow</span>(in <span>RowSpecification</span> row, in DOMString action); // required if getRowClasses ever includes 'deletable' or if <span title="dom-provider-.performActionOnRow">.performActionOnRow</span>() is ever invoked on the datagrid
  void <span title="dom-provider-performActionOnCell">performActionOnCell</span>(in <span>RowSpecification</span> row, in unsigned long column, in DOMString action); // required if .performActionOnCell() is ever invoked on the datagrid
-->};</pre>
  <!-- based on http://lxr.mozilla.org/seamonkey/source/layout/xul/base/src/tree/public/nsITreeView.idl -->

  <p>The <code><a
   href="#datagriddataprovider">DataGridDataProvider</a></code> interface
   represents the interface that objects must implement to be used as custom
   data views for <code><a href="#datagrid0">datagrid</a></code> elements.

  <p>Not all the methods are required. The minimum number of methods that
   must be implemented in a useful view is two: the <code
   title=dom-provider-getRowCount><a
   href="#getrowcount">getRowCount()</a></code> and <code
   title=dom-provider-getCellData><a
   href="#getcelldata">getCellData()</a></code> methods.

  <p>Once the object is written, it must be hooked up to the <code><a
   href="#datagrid0">datagrid</a></code> using the <dfn id=data2
   title=dom-datagrid-data><code>data</code></dfn> DOM attribute.

  <p>The following methods may be usefully implemented:

  <dl>
   <dt><dfn id=initialize title=dom-provider-initialize><code>initialize(<var
    title="">datagrid</var>)</code></dfn>

   <dd>Called by the <code><a href="#datagrid0">datagrid</a></code> element
    (the one given by the <var title="">datagrid</var> argument) after it has
    first populated itself. This would typically be used to set the initial
    selection of the <code><a href="#datagrid0">datagrid</a></code> element
    when it is first loaded. The data provider could also use this method
    call to register a <code title=event-select><a
    href="#select">select</a></code> event handler on the <code><a
    href="#datagrid0">datagrid</a></code> in order to monitor selection
    changes.

   <dt><dfn id=getrowcount
    title=dom-provider-getRowCount><code>getRowCount(<var
    title="">row</var>)</code></dfn>

   <dd>Must return the number of rows that are children of the specified <var
    title="">row</var>, including rows that are off-screen. If <var
    title="">row</var> is empty, then the number of rows at the top level
    must be returned. If the value that this method would return for a given
    <var title="">row</var> changes, the relevant update methods on the
    <code><a href="#datagrid0">datagrid</a></code> must be called first.
    Otherwise, this method must always return the same number. For a list (as
    opposed to a tree), this method must return 0 whenever it is called with
    a <var title="">row</var> identifier that is not empty.

   <dt><dfn id=getchildatposition
    title=dom-provider-getChildAtPosition><code>getChildAtPosition(<var
    title="">parentRow</var>, <var title="">position</var>)</code></dfn>

   <dd>Must return the index of the row that is a child of <var
    title="">parentRow</var> and that is to be positioned as the <var
    title="">position</var>th row under <var title="">parentRow</var> when
    rendering the children of <var title="">parentRow</var>. If <var
    title="">parentRow</var> is empty, then <var title="">position</var>
    refers to the <var title="">position</var>th row at the top level of the
    data grid. May be omitted if the rows are always to be sorted in the
    natural order. (The natural order is the one where the method always
    returns <var title="">position</var>.) For a given <var
    title="">parentRow</var>, this method must never return the same value
    for different values of <var title="">position</var>. The returned value
    <var title="">x</var> must be in the range 0&nbsp;&le;&nbsp;<var
    title="">x</var>&nbsp;&lt;&nbsp;<var title="">n</var>, where <var
    title="">n</var> is the value returned by <code
    title=dom-provider-getRowCount><a href="#getrowcount">getRowCount(<var
    title="">parentRow</var>)</a></code>.

   <dt><dfn id=getcolumncount
    title=dom-provider-getColumnCount><code>getColumnCount()</code></dfn>

   <dd>Must return the number of columns currently in the data model
    (including columns that might be hidden). May be omitted if there is only
    one column. If the value that this method would return changes, the
    <code><a href="#datagrid0">datagrid</a></code>'s <code
    title=dom-datagrid-updateEverything><a
    href="#updateeverything">updateEverything()</a></code> method must be
    called.

   <dt><dfn id=getcaptiontext
    title=dom-provider-getCaptionText><code>getCaptionText(<var
    title="">column</var>)</code></dfn>

   <dd>Must return the caption, or label, for column <var
    title="">column</var>. May be omitted if the columns have no captions. If
    the value that this method would return changes, the <code><a
    href="#datagrid0">datagrid</a></code>'s <code
    title=dom-datagrid-updateColumnChanged><a
    href="#updatecolumnchanged">updateColumnChanged()</a></code> method must
    be called with the appropriate column index.

   <dt><dfn id=getcaptionclasses
    title=dom-provider-getCaptionClasses><code>getCaptionClasses(<var
    title="">column</var>, <var title="">classes</var>)</code></dfn>

   <dd>Must add the classes that apply to column <var title="">column</var>
    to the <var title="">classes</var> object. May be omitted if the columns
    have no special classes. If the classes that this method would add
    changes, the <code><a href="#datagrid0">datagrid</a></code>'s <code
    title=dom-datagrid-updateColumnChanged><a
    href="#updatecolumnchanged">updateColumnChanged()</a></code> method must
    be called with the appropriate column index. Some classes have <a
    href="#datagridClassSummary">predefined meanings</a>.

   <dt><dfn id=getrowimage
    title=dom-provider-getRowImage><code>getRowImage(<var
    title="">row</var>)</code></dfn>

   <dd>Must return a URI to an image that represents row <var
    title="">row</var>, or the empty string if there is no applicable image.
    May be omitted if no rows have associated images. If the value that this
    method would return changes, the <code><a
    href="#datagrid0">datagrid</a></code>'s update methods must be called to
    update the row in question.

   <dt><dfn id=getrowmenu title=dom-provider-getRowMenu><code>getRowMenu(<var
    title="">row</var>)</code></dfn>

   <dd>Must return an <code><a
    href="#htmlmenuelement">HTMLMenuElement</a></code> object that is to be
    used as a context menu for row <var title="">row</var>, or null if there
    is no particular context menu. May be omitted if none of the rows have a
    special context menu. As this method is called immediately before showing
    the menu in question, no precautions need to be taken if the return value
    of this method changes.

   <dt><dfn id=getrowclasses
    title=dom-provider-getRowClasses><code>getRowClasses(<var
    title="">row</var>, <var title="">classes</var>)</code></dfn>

   <dd>Must add the classes that apply to row <var title="">row</var> to the
    <var title="">classes</var> object. May be omitted if the rows have no
    special classes. If the classes that this method would add changes, the
    <code><a href="#datagrid0">datagrid</a></code>'s update methods must be
    called to update the row in question. Some classes have <a
    href="#datagridClassSummary">predefined meanings</a>.

   <dt><dfn id=getcelldata
    title=dom-provider-getCellData><code>getCellData(<var title="">row</var>,
    <var title="">column</var>)</code></dfn>

   <dd>Must return the value of the cell on row <var title="">row</var> in
    column <var title="">column</var>. For text cells, this must be the text
    to show for that cell. For <a href="#progress1"
    title=datagrid-cell-class-progress>progress bar cells</a>, this must be
    either a floating point number in the range 0.0 to 1.0 (converted to a
    string representation<!-- XXX this isn't
   technically enough to define what the author must be doing here,
   but let's let that slide until someone notices -->),
    indicating the fraction of the progress bar to show as full (1.0 meaning
    complete), or the empty string, indicating an indeterminate progress bar.
    If the value that this method would return changes, the <code><a
    href="#datagrid0">datagrid</a></code>'s update methods must be called to
    update the rows that changed. If only one cell changed, the <code
    title=dom-datagrid-updateCellChanged><a
    href="#updatecellchanged">updateCellChanged()</a></code> method may be
    used.

   <dt><dfn id=getcellclasses
    title=dom-provider-getCellClasses><code>getCellClasses(<var
    title="">row</var>, <var title="">column</var>, <var
    title="">classes</var>)</code></dfn>

   <dd>Must add the classes that apply to the cell on row <var
    title="">row</var> in column <var title="">column</var> to the <var
    title="">classes</var> object. May be omitted if the cells have no
    special classes. If the classes that this method would add changes, the
    <code><a href="#datagrid0">datagrid</a></code>'s update methods must be
    called to update the rows or cells in question. Some classes have <a
    href="#datagridClassSummary">predefined meanings</a>.

   <dt><dfn id=togglecolumnsortstate
    title=dom-provider-toggleColumnSortState><code>toggleColumnSortState(<var
    title="">column</var>)</code></dfn>

   <dd>Called by the <code><a href="#datagrid0">datagrid</a></code> when the
    user tries to sort the data using a particular column <var
    title="">column</var>. The data provider must update its state so that
    the <code title=dom-provider-getChildAtPosition><a
    href="#getchildatposition">GetChildAtPosition()</a></code> method returns
    the new order, and the classes of the columns returned by <code
    title=dom-provider-getCaptionClasses><a
    href="#getcaptionclasses">getCaptionClasses()</a></code> represent the
    new sort status. There is no need to tell the <code><a
    href="#datagrid0">datagrid</a></code> that it the data has changed, as
    the <code><a href="#datagrid0">datagrid</a></code> automatically assumes
    that the entire data model will need updating.

   <dt><dfn id=setcellcheckedstate
    title=dom-provider-setCellCheckedState><code>setCellCheckedState(<var
    title="">row</var>, <var title="">column</var>, <var
    title="">state</var>)</code></dfn>

   <dd>Called by the <code><a href="#datagrid0">datagrid</a></code> when the
    user changes the state of a checkbox cell on row <var title="">row</var>,
    column <var title="">column</var>. The checkbox should be toggled to the
    state given by <var title="">state</var>, which is a positive integer (1)
    if the checkbox is to be checked, zero (0) if it is to be unchecked, and
    a negative number (-1) if it is to be set to the indeterminate state.
    There is no need to tell the <code><a
    href="#datagrid0">datagrid</a></code> that the cell has changed, as the
    <code><a href="#datagrid0">datagrid</a></code> automatically assumes that
    the given cell will need updating.

   <dt><dfn id=cyclecell title=dom-provider-cycleCell><code>cycleCell(<var
    title="">row</var>, <var title="">column</var>)</code></dfn>

   <dd>Called by the <code><a href="#datagrid0">datagrid</a></code> when the
    user changes the state of a cyclable cell on row <var title="">row</var>,
    column <var title="">column</var>. The data provider should change the
    state of the cell to the new state, as appropriate. There is no need to
    tell the <code><a href="#datagrid0">datagrid</a></code> that the cell has
    changed, as the <code><a href="#datagrid0">datagrid</a></code>
    automatically assumes that the given cell will need updating.

   <dt><dfn id=editcell title=dom-provider-editCell><code>editCell(<var
    title="">row</var>, <var title="">column</var>, <var
    title="">data</var>)</code></dfn>

   <dd>Called by the <code><a href="#datagrid0">datagrid</a></code> when the
    user edits the cell on row <var title="">row</var>, column <var
    title="">column</var>. The new value of the cell is given by <var
    title="">data</var>. The data provider should update the cell
    accordingly. There is no need to tell the <code><a
    href="#datagrid0">datagrid</a></code> that the cell has changed, as the
    <code><a href="#datagrid0">datagrid</a></code> automatically assumes that
    the given cell will need updating.</dd>
   <!--XXXPA
  void performAction(in DOMString action); // required if .performAction() is ever invoked on the datagrid
  void performActionOnRow(in <span>RowSpecification</span> row, in DOMString action); // required if getRowClasses ever includes 'deletable' or if .performActionOnRow() is ever invoked on the datagrid
  void performActionOnCell(in <span>RowSpecification</span> row, in unsigned long column, in DOMString action); // required if .performActionOnCell() is ever invoked on the datagrid
-->
  </dl>

  <p>The following classes (for rows, columns, and cells) may be usefully
   used in conjunction with this interface:

  <table id=datagridClassSummary>
   <tbody>
    <tr>
     <th>Class name

     <th>Applies to

     <th>Description

    <tr>
     <td><!--checked--><dfn id=checked
      title=datagrid-cell-class-checked><code>checked</code></dfn>

     <td>Cells

     <td>The cell has a checkbox and it is checked. (The <code
      title=datagrid-cell-class-cyclable><a
      href="#cyclable">cyclable</a></code> and <code
      title=datagrid-cell-class-progress><a
      href="#progress1">progress</a></code> classes override this, though.)

    <tr>
     <td><!--cyclable--><dfn id=cyclable
      title=datagrid-cell-class-cyclable><code>cyclable</code></dfn>

     <td>Cells

     <td>The cell can be cycled through multiple values. (The <code
      title=datagrid-cell-class-progress><a
      href="#progress1">progress</a></code> class overrides this, though.)

    <tr>
     <td><!--editable--><dfn id=editable
      title=datagrid-cell-class-editable><code>editable</code></dfn>

     <td>Cells

     <td>The cell can be edited. (The <code
      title=datagrid-cell-class-cyclable><a
      href="#cyclable">cyclable</a></code>, <code
      title=datagrid-cell-class-progress><a
      href="#progress1">progress</a></code>, <code
      title=datagrid-cell-class-checked><a
      href="#checked">checked</a></code>, <code
      title=datagrid-cell-class-checked><a
      href="#checked">unchecked</a></code> and <code
      title=datagrid-cell-class-checked><a
      href="#checked">indeterminate</a></code> classes override this,
      though.)

    <tr>
     <td><!--header--><dfn id=header0
      title=datagrid-row-class-header><code>header</code></dfn>

     <td>Rows

     <td>The row is a heading, not a data row.

    <tr>
     <td><!--indeterminate--><dfn id=indeterminate
      title=datagrid-cell-class-indeterminate><code>indeterminate</code></dfn>

     <td>Cells

     <td>The cell has a checkbox, and it can be set to an indeterminate
      state. If neither the <code title=datagrid-cell-class-checked><a
      href="#checked">checked</a></code> nor <code
      title=datagrid-cell-class-checked><a
      href="#checked">unchecked</a></code> classes are present, then the
      checkbox is in that state, too. (The <code
      title=datagrid-cell-class-cyclable><a
      href="#cyclable">cyclable</a></code> and <code
      title=datagrid-cell-class-progress><a
      href="#progress1">progress</a></code> classes override this, though.)

    <tr>
     <td><!--initially-hidden--><dfn id=initially-hidden
      title=datagrid-column-class-initially-hidden><code>initially-hidden</code></dfn>

     <td>Columns

     <td>The column will not be shown when the <code><a
      href="#datagrid0">datagrid</a></code> is initially rendered. If this
      class is not present on the column when the <code><a
      href="#datagrid0">datagrid</a></code> is initially rendered, the column
      will be visible if space allows.

    <tr>
     <td><!--initially-closed--><dfn id=initially-closed
      title=datagrid-row-class-initially-closed><code>initially-closed</code></dfn>

     <td>Rows

     <td>The row will be closed when the <code><a
      href="#datagrid0">datagrid</a></code> is initially rendered. If neither
      this class nor the <code title=datagrid-row-class-initially-open><a
      href="#initially-open">initially-open</a></code> class is present on
      the row when the <code><a href="#datagrid0">datagrid</a></code> is
      initially rendered, the initial state will depend on platform
      conventions.

    <tr>
     <td><!--initially-open--><dfn id=initially-open
      title=datagrid-row-class-initially-open><code>initially-open</code></dfn>

     <td>Rows

     <td>The row will be opened when the <code><a
      href="#datagrid0">datagrid</a></code> is initially rendered. If neither
      this class nor the <code title=datagrid-row-class-initially-closed><a
      href="#initially-closed">initially-closed</a></code> class is present
      on the row when the <code><a href="#datagrid0">datagrid</a></code> is
      initially rendered, the initial state will depend on platform
      conventions.

    <tr>
     <td><!--progress--><dfn id=progress1
      title=datagrid-cell-class-progress><code>progress</code></dfn>

     <td>Cells

     <td>The cell is a progress bar.

    <tr>
     <td><!--reversed--><dfn id=reversed
      title=datagrid-column-class-reversed><code>reversed</code></dfn>

     <td>Columns

     <td>If the cell is sorted, the sort direction is descending, instead of
      ascending.

    <tr>
     <td><!--selectable-separator--><dfn id=selectable-separator
      title=datagrid-row-class-selectable-separator><code>selectable-separator</code></dfn>

     <td>Rows

     <td>The row is a normal, selectable, data row, except that instead of
      having data, it only has a separator. (The <code
      title=datagrid-row-class-header><a href="#header0">header</a></code>
      and <code title=datagrid-row-class-separator><a
      href="#separator">separator</a></code> classes override this, though.)

    <tr>
     <td><!--separator--><dfn id=separator
      title=datagrid-row-class-separator><code>separator</code></dfn>

     <td>Rows

     <td>The row is a separator row, not a data row. (The <code
      title=datagrid-row-class-header><a href="#header0">header</a></code>
      class overrides this, though.)

    <tr>
     <td><!--sortable--><dfn id=sortable
      title=datagrid-column-class-sortable><code>sortable</code></dfn>

     <td>Columns

     <td>The data can be sorted by this column.

    <tr>
     <td><!--sorted--><dfn id=sorted
      title=datagrid-column-class-sorted><code>sorted</code></dfn>

     <td>Columns

     <td>The data is sorted by this column. Unless the <code
      title=datagrid-column-class-reversed><a
      href="#reversed">reversed</a></code> class is also present, the sort
      direction is ascending.

    <tr>
     <td><!--unchecked--><dfn id=unchecked
      title=datagrid-cell-class-unchecked><code>unchecked</code></dfn>

     <td>Cells

     <td>The cell has a checkbox and, unless the <code
      title=datagrid-cell-class-checked><a href="#checked">checked</a></code>
      class is present as well, it is unchecked. (The <code
      title=datagrid-cell-class-cyclable><a
      href="#cyclable">cyclable</a></code> and <code
      title=datagrid-cell-class-progress><a
      href="#progress1">progress</a></code> classes override this, though.)
    </tr>
    <!--XXXPA
   <tr>
    <td><!- -deletable- -><dfn title="datagrid-row-class-deletable"><code>deletable</code></dfn></td>
    <td>Rows</td>
    <td></td>
   </tr>
-->
  </table>

  <h5 id=the-default><span class=secno>3.18.2.4. </span>The default data
   provider</h5>

  <p>The user agent must supply a default data provider for the case where
   the <code><a href="#datagrid0">datagrid</a></code>'s <code
   title=dom-datagrid-data><a href="#data2">data</a></code> attribute is
   null. It must act as described in this section.

  <p>The behaviour of the default data provider depends on the nature of the
   first element child of the <code><a href="#datagrid0">datagrid</a></code>.

  <dl class=switch>
   <dt>While the first element child is a <code><a
    href="#table">table</a></code> element

   <dd>
    <p><strong><code title=dom-provider-getRowCount><a
     href="#getrowcount">getRowCount(<var
     title="">row</var>)</a></code></strong>: The number of rows returned by
     the default data provider for the root of the tree (when <var
     title="">row</var> is empty) must be the total number of <code><a
     href="#tr">tr</a></code> elements that are children of <code><a
     href="#tbody">tbody</a></code> elements that are children of the
     <code><a href="#table">table</a></code>, if there are any such child
     <code><a href="#tbody">tbody</a></code> elements. If there are no such
     <code><a href="#tbody">tbody</a></code> elements then the number of rows
     returned for the root must be the number of <code><a
     href="#tr">tr</a></code> elements that are children of the <code><a
     href="#table">table</a></code>.</p>

    <p>When <var title="">row</var> is not empty, the number of rows returned
     must be zero.</p>

    <p class=note>The <code><a href="#table">table</a></code>-based default
     data provider cannot represent a tree.</p>

    <p class=note>Rows in <code><a href="#thead0">thead</a></code> elements
     do not contribute to the number of rows returned, although they do
     affect the columns and column captions. Rows in <code><a
     href="#tfoot0">tfoot</a></code> elements are <a href="#ignored"
     title=ignore>ignored</a> completely by this algorithm.</p>

    <p id=defaultDataProviderTableMapper><strong><code
     title=dom-provider-getChildAtPosition><a
     href="#getchildatposition">getChildAtPosition(<var title="">row</var>,
     <var title="">i</var>)</a></code></strong>: The default data provider
     must return the mapping appropriate to the <a
     href="#defaultDataProviderTableSort">current sort order</a>.</p>

    <p><strong><code title=dom-provider-getColumnCount><a
     href="#getcolumncount">getColumnCount()</a></code></strong>: The number
     of columns returned must be the number of <code><a
     href="#td">td</a></code> element children in the first <code><a
     href="#tr">tr</a></code> element child of the first <code><a
     href="#tbody">tbody</a></code> element child of the <code><a
     href="#table">table</a></code>, if there are any such <code><a
     href="#tbody">tbody</a></code> elements. If there are no such <code><a
     href="#tbody">tbody</a></code> elements, then it must be the number of
     <code><a href="#td">td</a></code> element children in the first <code><a
     href="#tr">tr</a></code> element child of the <code><a
     href="#table">table</a></code>, if any, or otherwise 1. If the number
     that would be returned by these rules is 0, then 1 must be returned
     instead.</p>

    <p><strong><code title=dom-provider-getCaptionText><a
     href="#getcaptiontext">getCaptionText(<var
     title="">i</var>)</a></code></strong>: If the <code><a
     href="#table">table</a></code> has no <code><a
     href="#thead0">thead</a></code> element child, or if its first <code><a
     href="#thead0">thead</a></code> element child has no <code><a
     href="#tr">tr</a></code> element child, the default data provider must
     return the empty string for all captions. Otherwise, the value of the
     <code><a href="#textcontent">textContent</a></code> attribute of the
     <var title="">i</var>th <code><a href="#th">th</a></code> element child
     of the first <code><a href="#tr">tr</a></code> element child of the
     first <code><a href="#thead0">thead</a></code> element child of the
     <code><a href="#table">table</a></code> element must be returned. If
     there is no such <code><a href="#th">th</a></code> element, the empty
     string must be returned.</p>

    <p><strong><code title=dom-provider-getCaptionClasses><a
     href="#getcaptionclasses">getCaptionClasses(<var title="">i</var>, <var
     title="">classes</var>)</a></code></strong>: If the <code><a
     href="#table">table</a></code> has no <code><a
     href="#thead0">thead</a></code> element child, or if its first <code><a
     href="#thead0">thead</a></code> element child has no <code><a
     href="#tr">tr</a></code> element child, the default data provider must
     not add any classes for any of the captions. Otherwise, each class in
     the <code title=attr-class><a href="#class">class</a></code> attribute
     of the <var title="">i</var>th <code><a href="#th">th</a></code> element
     child of the first <code><a href="#tr">tr</a></code> element child of
     the first <code><a href="#thead0">thead</a></code> element child of the
     <code><a href="#table">table</a></code> element must be added to the
     <var title="">classes</var>. If there is no such <code><a
     href="#th">th</a></code> element, no classes must be added. The user
     agent must then:</p>

    <ol>
     <li>Remove the <code title=datagrid-column-class-sorted><a
      href="#sorted">sorted</a></code> and <code
      title=datagrid-column-class-reversed><a
      href="#reversed">reversed</a></code> classes.

     <li>If the <code><a href="#table">table</a></code> element has a <code
      title=attr-class><a href="#class">class</a></code> attribute that
      includes the <code title="">sortable</code> class, add the <code
      title=datagrid-column-class-sortable><a
      href="#sortable">sortable</a></code> class.

     <li>If the column is the one currently being used to sort the data, add
      the <code title=datagrid-column-class-sorted><a
      href="#sorted">sorted</a></code> class.

     <li>If the column is the one currently being used to sort the data, and
      it is sorted in descending order, add the <code
      title=datagrid-column-class-reversed><a
      href="#reversed">reversed</a></code> class as well.
    </ol>

    <p>The various row- and cell- related methods operate relative to a
     particular element, the element of the row or cell specified by their
     arguments.</p>

    <p><strong>For rows</strong>: Since the default data provider for a
     <code><a href="#table">table</a></code> always returns 0 as the number
     of children for any row other than the root, the path to the row passed
     to these methods will always consist of a single number. In the prose
     below, this number is referred to as <var title="">i</var>.</p>

    <p>If the <code><a href="#table">table</a></code> has <code><a
     href="#tbody">tbody</a></code> element children, the element for the
     <var title="">i</var>th row is the <var title="">i</var>th <code><a
     href="#tr">tr</a></code> element that is a child of a <code><a
     href="#tbody">tbody</a></code> element that is a child of the <code><a
     href="#table">table</a></code> element. If the <code><a
     href="#table">table</a></code> does not have <code><a
     href="#tbody">tbody</a></code> element children, then the element for
     the <var title="">i</var>th real row is the <var title="">i</var>th
     <code><a href="#tr">tr</a></code> element that is a child of the
     <code><a href="#table">table</a></code> element.</p>

    <p><strong>For cells</strong>: Given a row and its element, the row's
     <var title="">i</var>th cell's element is the <var title="">i</var>th
     <code><a href="#td">td</a></code> element child of the row element.</p>

    <p class=note>The <code>colspan</code> and <code>rowspan</code>
     attributes are <a href="#ignored" title=ignore>ignored</a> by this
     algorithm.</p>

    <p><strong><code title=dom-provider-getRowImage><a
     href="#getrowimage">getRowImage(<var
     title="">i</var>)</a></code></strong>: If the row's first cell's element
     has an <code><a href="#img">img</a></code> element child, then the URI
     of the row's image is the URI of the first <code><a
     href="#img">img</a></code> element child of the row's first cell's
     element. Otherwise, the URI of the row's image is the empty string.</p>
    <!-- XXX well. that sentence could
    have gone better, that's for sure. -->
    
    <p><strong><code title=dom-provider-getRowMenu><a
     href="#getrowmenu">getRowMenu(<var
     title="">i</var>)</a></code></strong>: If the row's first cell's element
     has a <code><a href="#menu">menu</a></code> element child, then the
     row's menu is the first <code><a href="#menu">menu</a></code> element
     child of the row's first cell's element. Otherwise, the row has no menu.</p>

    <p><strong><code title=dom-provider-getRowClasses><a
     href="#getrowclasses">getRowClasses(<var title="">i</var>, <var
     title="">classes</var>)</a></code></strong>: The default data provider
     must never add a class to the row's classes.</p>

    <p id=defaultDataProviderTableSort><strong><code
     title=dom-provider-toggleColumnSortState><a
     href="#togglecolumnsortstate">toggleColumnSortState(<var
     title="">i</var>)</a></code></strong>: If the data is already being
     sorted on the given column, then the user agent must change the current
     sort mapping to be the inverse of the current sort mapping; if the sort
     order was ascending before, it is now descending, otherwise it is now
     ascending. Otherwise, if the current sort column is another column, or
     the data model is currently not sorted, the user agent must create a new
     mapping, which maps rows in the data model to rows in the DOM so that
     the rows in the data model are sorted by the specified column, in
     ascending order. (Which sort comparison operator to use is left up to
     the UA to decide.)</p>

    <p>When the sort mapping is changed, the values returned by the <code
     title=dom-provider-getChildAtPosition><a
     href="#getchildatposition">getChildAtPosition()</a></code> method for
     the default data provider <a href="#defaultDataProviderTableMapper">will
     change appropriately</a>.</p>

    <p><strong><code title=dom-provider-getCellData><a
     href="#getcelldata">getCellData(<var title="">i</var>, <var
     title="">j</var>)</a></code>, <code title=dom-provider-getCellClasses><a
     href="#getcellclasses">getCellClasses(<var title="">i</var>, <var
     title="">j</var>, <var title="">classes</var>)</a></code>, <code
     title=dom-provider-setCellCheckedState><a
     href="#setcellcheckedstate">getCellCheckedState(<var title="">i</var>,
     <var title="">j</var>, <var title="">state</var>)</a></code>, <code
     title=dom-provider-cycleCell><a href="#cyclecell">cycleCell(<var
     title="">i</var>, <var title="">j</var>)</a></code>, and <code
     title=dom-provider-editCell><a href="#editcell">editCell(<var
     title="">i</var>, <var title="">j</var>, <var
     title="">data</var>)</a></code></strong>: See <a
     href="#commonDefaultDataGridMethodDefinitions">the common definitions
     below</a>.</p>

    <p>The data provider must call the <code><a
     href="#datagrid0">datagrid</a></code>'s update methods appropriately
     whenever the descendants of the <code><a
     href="#datagrid0">datagrid</a></code> mutate. For example, if a <code><a
     href="#tr">tr</a></code> is removed, then the <code
     title=dom-datagrid-updateRowsRemoved><a
     href="#updaterowsremoved">updateRowsRemoved()</a></code> methods would
     probably need to be invoked, and any change to a cell or its descendants
     must cause the cell to be updated. If the <code><a
     href="#table">table</a></code> element stops being the first child of
     the <code><a href="#datagrid0">datagrid</a></code>, then the data
     provider must call the <code title=dom-datagrid-updateEverything><a
     href="#updateeverything">updateEverything()</a></code> method on the
     <code><a href="#datagrid0">datagrid</a></code>. Any change to a cell
     that is in the column that the data provider is currently using as its
     sort column must also cause the sort to be reperformed, with a call to
     <code title=dom-datagrid-updateEverything><a
     href="#updateeverything">updateEverything()</a></code> if the change did
     affect the sort order.</p>

   <dt>While the first element child is a <code>select</code> or
    <code>datalist</code> element

   <dd>
    <p>The default data provider must return 1 for the column count, the
     empty string for the column's caption, and must not add any classes to
     the column's classes.</p>

    <p>For the rows, assume the existence of a node filter view of the
     descendants of the first element child of the <code><a
     href="#datagrid0">datagrid</a></code> element (the <code>select</code>
     or <code>datalist</code> element), that skips all nodes other than
     <code>optgroup</code> and <code>option</code> elements, as well as any
     descendents of any <code>option</code> elements.</p>

    <p>Given a path <var title="">row</var>, the corresponding element is the
     one obtained by drilling into the view, taking the child given by the
     path each time.</p>

    <div class=example>
     <p>Given the following XML markup:</p>

     <pre>&lt;datagrid>
 &lt;select>
  &lt;!-- the options and optgroups have had their labels and values removed
       to make the underlying structure clearer -->
  &lt;optgroup>
   &lt;option/>
   &lt;option/>
  &lt;/optgroup>
  &lt;optgroup>
   &lt;option/>
   &lt;optgroup id="a">
    &lt;option/>
    &lt;option/>
    &lt;bogus/>
    &lt;option id="b"/>
   &lt;/optgroup>
   &lt;option/>
  &lt;/optgroup>
 &lt;/select>
&lt;/datagrid></pre>

     <p>The path "1,1,2" would select the element with ID "b". In the
      filtered view, the text nodes, comment nodes, and bogus elements are
      ignored; so for instance, the element with ID "a" (path "1,1") has only
      3 child nodes in the view.</p>
    </div>

    <p><code title=dom-provider-getRowCount><a
     href="#getrowcount">getRowCount(<var title="">row</var>)</a></code> must
     drill through the view to find the element corresponding to the method's
     argument, and return the number of child nodes in the filtered view that
     the corresponding element has. (If the <var title="">row</var> is empty,
     the corresponding element is the <code>select</code> element at the root
     of the filtered view.)</p>

    <p><code title=dom-provider-getChildAtPosition><a
     href="#getchildatposition">getChildAtPosition(<var title="">row</var>,
     <var title="">position</var>)</a></code> must return <var
     title="">position</var>. (The <code>select</code>/<code>datalist</code>
     default data provider does not support sorting the data grid.)</p>

    <p><code title=dom-provider-getRowImage><a
     href="#getrowimage">getRowImage(<var title="">i</var>)</a></code> must
     return the empty string, <code title=dom-provider-getRowMenu><a
     href="#getrowmenu">getRowMenu(<var title="">i</var>)</a></code> must
     return null.</p>

    <p><code title=dom-provider-getRowClasses><a
     href="#getrowclasses">getRowClasses(<var title="">row</var>, <var
     title="">classes</var>)</a></code> must add the classes from the
     following list to <var title="">classes</var> when their condition is
     met:</p>

    <ul>
     <li>If the <var title="">row</var>'s corresponding element is an
      <code>optgroup</code> element: <code title=datagrid-row-class-header><a
      href="#header0">header</a></code>

     <li>If the <var title="">row</var>'s corresponding element contains
      other elements that are also in the view, and the element's <code
      title=attr-class><a href="#class">class</a></code> attribute contains
      the <code title="">closed</code> class: <code
      title=datagrid-row-class-initially-closed><a
      href="#initially-closed">initially-closed</a></code>

     <li>If the <var title="">row</var>'s corresponding element contains
      other elements that are also in the view, and the element's <code
      title=attr-class><a href="#class">class</a></code> attribute contains
      the <code title="">open</code> class: <code
      title=datagrid-row-class-initially-open><a
      href="#initially-open">initially-open</a></code>
    </ul>

    <p>The <code title=dom-provider-getCellData><a
     href="#getcelldata">getCellData(<var title="">row</var>, <var
     title="">cell</var>)</a></code> method must return the value of the
     <code title=attr-optgroup-label>label</code> attribute if the <var
     title="">row</var>'s corresponding element is an <code>optgroup</code>
     element, otherwise, if the <var title="">row</var>'s corresponding
     element is an <code>option</code>element, its <code
     title=attr-option-label>label</code> attribute if it has one, otherwise
     the value of its <code><a href="#textcontent">textContent</a></code> DOM
     attribute.</p>

    <p>The <code title=dom-provider-getCellClasses><a
     href="#getcellclasses">getCellClasses(<var title="">row</var>, <var
     title="">cell</var>, <var title="">classes</var>)</a></code> method must
     add no classes.</p>

    <p class=big-issue><!-- select-provider-selection
    XXX-->autoselect
     some rows when initialised, reflect the selection in the select, reflect
     the multiple attribute somehow.</p>

    <p>The data provider must call the <code><a
     href="#datagrid0">datagrid</a></code>'s update methods appropriately
     whenever the descendants of the <code><a
     href="#datagrid0">datagrid</a></code> mutate.</p>

   <dt>While the first element child is another element

   <dd>
    <p>The default data provider must return 1 for the column count, the
     empty string for the column's caption, and must not add any classes to
     the column's classes.</p>

    <p>For the rows, assume the existence of a node filter view of the
     descendants of the <code><a href="#datagrid0">datagrid</a></code> that
     skips all nodes other than <code><a href="#li">li</a></code>, <code><a
     href="#h1">h1</a></code>-<code><a href="#h6">h6</a></code>, and <code><a
     href="#hr">hr</a></code> elements, and skips any descendants of <code><a
     href="#menu">menu</a></code> elements.</p>

    <p>Given this view, each element in the view represents a row in the data
     model. The element corresponding to a path <var title="">row</var> is
     the one obtained by drilling into the view, taking the child given by
     the path each time. The element of the row of a particular method call
     is the element given by drilling into the view along the path given by
     the method's arguments.</p>

    <p><code title=dom-provider-getRowCount><a
     href="#getrowcount">getRowCount(<var title="">row</var>)</a></code> must
     return the number of child elements in this view for the given row, or
     the number of elements at the root of the view if the <var
     title="">row</var> is empty.</p>

    <div class=example>
     <p>In the following example, the elements are identified by the paths
      given by their child text nodes:</p>

     <pre>&lt;datagrid>
 &lt;ol>
  &lt;li> row 0 &lt;/li>
  &lt;li> row 1
   &lt;ol>
    &lt;li> row 1,0 &lt;/li>
   &lt;/ol>
  &lt;/li>
  &lt;li> row 2 &lt;/li>
 &lt;/ol>
&lt;/datagrid></pre>

     <p>In this example, only the <code><a href="#li">li</a></code> elements
      actually appear in the data grid; the <code><a href="#ol">ol</a></code>
      element does not affect the data grid's processing model.</p>
    </div>

    <p><code title=dom-provider-getChildAtPosition><a
     href="#getchildatposition">getChildAtPosition(<var title="">row</var>,
     <var title="">position</var>)</a></code> must return <var
     title="">position</var>. (The generic default data provider does not
     support sorting the data grid.)</p>

    <p><code title=dom-provider-getRowImage><a
     href="#getrowimage">getRowImage(<var title="">i</var>)</a></code> must
     return the URI of the image given by the first <code><a
     href="#img">img</a></code> element descendant (in the real DOM) of the
     row's element, that is not also a descendant of another element in the
     filtered view that is a descendant of the row's element.</p>

    <div class=example>
     <p>In the following example, the row with path "1,0" returns
      "http://example.com/a" as its image URI, and the other rows (including
      the row with path "1") return the empty string:</p>

     <pre>&lt;datagrid>
 &lt;ol>
  &lt;li> row 0 &lt;/li>
  &lt;li> row 1
   &lt;ol>
    &lt;li> row 1,0 &lt;img src="http://example.com/a" alt=""> &lt;/li>
   &lt;/ol>
  &lt;/li>
  &lt;li> row 2 &lt;/li>
 &lt;/ol>
&lt;/datagrid></pre>
    </div>

    <p><code title=dom-provider-getRowMenu><a
     href="#getrowmenu">getRowMenu(<var title="">i</var>)</a></code> must
     return the first <code><a href="#menu">menu</a></code> element
     descendant (in the real DOM) of the row's element, that is not also a
     descendant of another element in the filtered view that is a decsendant
     of the row's element. (This is analogous to the image case above.)</p>

    <p><code title=dom-provider-getRowClasses><a
     href="#getrowclasses">getRowClasses(<var title="">i</var>, <var
     title="">classes</var>)</a></code> must add the classes from the
     following list to <var title="">classes</var> when their condition is
     met:</p>

    <ul>
     <li>If the row's element contains other elements that are also in the
      view, and the element's <code title=attr-class><a
      href="#class">class</a></code> attribute contains the <code
      title="">closed</code> class: <code
      title=datagrid-row-class-initially-closed><a
      href="#initially-closed">initially-closed</a></code>

     <li>If the row's element contains other elements that are also in the
      view, and the element's <code title=attr-class><a
      href="#class">class</a></code> attribute contains the <code
      title="">open</code> class: <code
      title=datagrid-row-class-initially-open><a
      href="#initially-open">initially-open</a></code>

     <li>If the row's element is an <code><a
      href="#h1">h1</a></code>-<code><a href="#h6">h6</a></code> element:
      <code title=datagrid-row-class-header><a
      href="#header0">header</a></code>

     <li>If the row's element is an <code><a href="#hr">hr</a></code>
      element: <code title=datagrid-row-class-separator><a
      href="#separator">separator</a></code></li>
     <!--
     XXX no way to get selectable-separator -->
    </ul>

    <p>The <code title=dom-provider-getCellData><a
     href="#getcelldata">getCellData(<var title="">i</var>, <var
     title="">j</var>)</a></code>, <code title=dom-provider-getCellClasses><a
     href="#getcellclasses">getCellClasses(<var title="">i</var>, <var
     title="">j</var>, <var title="">classes</var>)</a></code>, <code
     title=dom-provider-setCellCheckedState><a
     href="#setcellcheckedstate">getCellCheckedState(<var title="">i</var>,
     <var title="">j</var>, <var title="">state</var>)</a></code>, <code
     title=dom-provider-cycleCell><a href="#cyclecell">cycleCell(<var
     title="">i</var>, <var title="">j</var>)</a></code>, and <code
     title=dom-provider-editCell><a href="#editcell">editCell(<var
     title="">i</var>, <var title="">j</var>, <var
     title="">data</var>)</a></code> methods must act as described in <a
     href="#commonDefaultDataGridMethodDefinitions">the common definitions
     below</a>, treating the row's element as being the cell's element.</p>

    <p class=big-issue id=generic-provider-selection>selection handling?</p>

    <p>The data provider must call the <code><a
     href="#datagrid0">datagrid</a></code>'s update methods appropriately
     whenever the descendants of the <code><a
     href="#datagrid0">datagrid</a></code> mutate.</p>

   <dt>Otherwise, while there is no element child

   <dd>
    <p>The data provider must return 0 for the number of rows, 1 for the
     number of columns, the empty string for the first column's caption, and
     must add no classes when asked for that column's classes. If the
     <code><a href="#datagrid0">datagrid</a></code>'s child list changes such
     that there is a first element child, then the data provider must call
     the <code title=dom-datagrid-updateEverything><a
     href="#updateeverything">updateEverything()</a></code> method on the
     <code><a href="#datagrid0">datagrid</a></code>.</p>
  </dl>

  <h6 id=commonDefaultDataGridMethodDefinitions><span class=secno>3.18.2.4.1.
   </span>Common default data provider method definitions for cells</h6>

  <p>These definitions are used for the cell-specific methods of the default
   data providers (other than in the
   <code>select</code>/<code>datalist</code> case). How they behave is based
   on the contents of an element that represents the cell given by their
   first two arguments. Which element that is is defined in the previous
   section.

  <dl>
   <dt>Cyclable cells

   <dd>
    <p>If the first element child of a cell's element is a
     <code>select</code> element that has a no <code
     title=attr-select-multiple>multiple</code> attribute and has at least
     one <code>option</code> element descendent, then the cell acts as a
     cyclable cell.</p>

    <p>The "current" <code>option</code> element is the selected
     <code>option</code> element, or the first <code>option</code> element if
     none is selected.</p>

    <p>The <code title=dom-provider-getCellData><a
     href="#getcelldata">getCellData()</a></code> method must return the
     <code><a href="#textcontent">textContent</a></code> of the current
     <code>option</code> element (the <code
     title=attr-option-label>label</code> attribute is <a href="#ignored"
     title=ignore>ignored</a> in this context as the <code>optgroup</code>s
     are not displayed).</p>

    <p>The <code title=dom-provider-getCellClasses><a
     href="#getcellclasses">getCellClasses()</a></code> method must add the
     <code title=datagrid-cell-class-cyclable><a
     href="#cyclable">cyclable</a></code> class and then all the classes of
     the current <code>option</code> element.</p>

    <p>The <code title=dom-provider-cycleCell><a
     href="#cyclecell">cycleCell()</a></code> method must change the
     selection of the <code>select</code> element such that the next
     <code>option</code> element after the current <code>option</code>
     element is the only one that is selected (in <a href="#tree-order">tree
     order</a>). If the current <code>option</code> element is the last
     <code>option</code> element descendent of the <code>select</code>, then
     the first <code>option</code> element descendent must be selected
     instead.</p>

    <p>The <code title=dom-provider-setCellCheckedState><a
     href="#setcellcheckedstate">setCellCheckedState()</a></code> and <code
     title=dom-provider-editCell><a href="#editcell">editCell()</a></code>
     methods must do nothing.</p>

   <dt>Progress bar cells

   <dd>
    <p>If the first element child of a cell's element is a <code><a
     href="#progress">progress</a></code> element, then the cell acts as a
     progress bar cell.</p>

    <p>The <code title=dom-provider-getCellData><a
     href="#getcelldata">getCellData()</a></code> method must return the
     value returned by the <code><a href="#progress">progress</a></code>
     element's <code title=dom-progress-position><a
     href="#position">position</a></code> DOM attribute.</p>

    <p>The <code title=dom-provider-getCellClasses><a
     href="#getcellclasses">getCellClasses()</a></code> method must add the
     <code title=datagrid-cell-class-progress><a
     href="#progress1">progress</a></code> class.</p>

    <p>The <code title=dom-provider-setCellCheckedState><a
     href="#setcellcheckedstate">setCellCheckedState()</a></code>, <code
     title=dom-provider-cycleCell><a
     href="#cyclecell">cycleCell()</a></code>, and <code
     title=dom-provider-editCell><a href="#editcell">editCell()</a></code>
     methods must do nothing.</p>

   <dt>Checkbox cells

   <dd>
    <p>If the first element child of a cell's element is an
     <code>input</code> element that has a <code
     title=attr-input-type>type</code> attribute with the value <code
     title="">checkbox</code>, then the cell acts as a check box cell.</p>

    <p>The <code title=dom-provider-getCellData><a
     href="#getcelldata">getCellData()</a></code> method must return the
     <code><a href="#textcontent">textContent</a></code> of the cell element.</p>

    <p>The <code title=dom-provider-getCellClasses><a
     href="#getcellclasses">getCellClasses()</a></code> method must add the
     <code title=datagrid-cell-class-checked><a
     href="#checked">checked</a></code> class if the <code>input</code>
     element is <span title=dom-input-checked>checked</span>, and the <code
     title=datagrid-cell-class-unchecked><a
     href="#unchecked">unchecked</a></code> class otherwise.</p>

    <p>The <code title=dom-provider-setCellCheckedState><a
     href="#setcellcheckedstate">setCellCheckedState()</a></code> method must
     set the <code>input</code> element's checkbox <span
     title=dom-input-checked>state</span> to checked if the method's third
     argument is 1, and to unchecked otherwise.</p>

    <p>The <code title=dom-provider-cycleCell><a
     href="#cyclecell">cycleCell()</a></code> and <code
     title=dom-provider-editCell><a href="#editcell">editCell()</a></code>
     methods must do nothing.</p>

   <dt>Editable cells

   <dd>
    <p>If the first element child of a cell's element is an
     <code>input</code> element that has a <code
     title=attr-input-type>type</code> attribute with the value <code
     title="">text</code> or that has no <code
     title=attr-input-type>type</code> attribute at all, then the cell acts
     as an editable cell.</p>

    <p>The <code title=dom-provider-getCellData><a
     href="#getcelldata">getCellData()</a></code> method must return the
     <code title=dom-input-value>value</code> of the <code>input</code>
     element.</p>

    <p>The <code title=dom-provider-getCellClasses><a
     href="#getcellclasses">getCellClasses()</a></code> method must add the
     <code title=datagrid-cell-class-editable><a
     href="#editable">editable</a></code> class.</p>

    <p>The <code title=dom-provider-editCell><a
     href="#editcell">editCell()</a></code> method must set the
     <code>input</code> element's <code title=dom-input-value>value</code>
     DOM attribute to the value of the third argument to the method.</p>

    <p>The <code title=dom-provider-setCellCheckedState><a
     href="#setcellcheckedstate">setCellCheckedState()</a></code> and <code
     title=dom-provider-cycleCell><a href="#cyclecell">cycleCell()</a></code>
     methods must do nothing.</p>
  </dl>
  <!-- XXX Calculated cells, like in spreadsheets? -->

  <h5 id=populating><span class=secno>3.18.2.5. </span>Populating the
   <code><a href="#datagrid0">datagrid</a></code> element</h5>

  <p>A <code><a href="#datagrid0">datagrid</a></code> must be disabled until
   its end tag has been parsed (in the case of a <code><a
   href="#datagrid0">datagrid</a></code> element in the original document
   markup) or until it has been inserted into the document (in the case of a
   dynamically created element). After that point, the element must fire a
   single <code title=event-load><a href="#load0">load</a></code> event at
   itself, which doesn't bubble and cannot be canceled.

  <p class=big-issue>The end-tag parsing thing should be moved to the parsing
   section.

  <p>The <code><a href="#datagrid0">datagrid</a></code> must then populate
   itself using the data provided by the data provider assigned to the <code
   title=dom-datagrid-data><a href="#data2">data</a></code> DOM attribute.
   After the view is populated (using the methods described below), the
   <code><a href="#datagrid0">datagrid</a></code> must invoke the <code
   title=dom-provider-initialize><a
   href="#initialize">initialize()</a></code> method on the data provider
   specified by the <code title=dom-datagrid-data><a
   href="#data2">data</a></code> attribute, passing itself (the <code><a
   href="#htmldatagridelement">HTMLDataGridElement</a></code> object) as the
   only argument.

  <p>When the <code title=dom-datagrid-data><a href="#data2">data</a></code>
   attribute is null, the <code><a href="#datagrid0">datagrid</a></code> must
   use the default data provider described in the previous section.

  <p>To obtain data from the data provider, the element must invoke methods
   on the data provider object in the following ways:

  <dl>
   <dt>To determine the total number of columns

   <dd>Invoke the <code title=dom-provider-getColumnCount><a
    href="#getcolumncount">getColumnCount()</a></code> method with no
    arguments. The return value is the number of columns. If the return value
    is zero or negative, not an integer, or simply not a numeric type, or if
    the method is not defined, then 1 must be used instead.

   <dt>To get the captions to use for the columns

   <dd>Invoke the <code title=dom-provider-getCaptionText><a
    href="#getcaptiontext">getCaptionText()</a></code> method with the index
    of the column in question. The index <var title="">i</var> must be in the
    range 0 &le; <var title="">i</var> &lt; <var title="">N</var>, where <var
    title="">N</var> is the total number of columns. The return value is the
    string to use when referring to that column. If the method returns null
    or the empty string, the column has no caption. If the method is not
    defined, then none of the columns have any captions.

   <dt>To establish what classes apply to a column

   <dd>Invoke the <code title=dom-provider-getCaptionClasses><a
    href="#getcaptionclasses">getCaptionClasses()</a></code> method with the
    index of the column in question, and an object implementing the <code><a
    href="#domtokenlist0">DOMTokenList</a></code> interface, associated with
    an anonymous empty string. The index <var title="">i</var> must be in the
    range 0 &le; <var title="">i</var> &lt; <var title="">N</var>, where <var
    title="">N</var> is the total number of columns. The tokens contained in
    the string underlying <code><a
    href="#domtokenlist0">DOMTokenList</a></code> object when the method
    returns represent the classes that apply to the given column. If the
    method is not defined, no classes apply to the column.

   <dt>To establish whether a column should be initially included in the
    visible columns

   <dd>Check whether the <code
    title=datagrid-column-class-initially-hidden><a
    href="#initially-hidden">initially-hidden</a></code> class applies to the
    column. If it does, then the column should not be initially included; if
    it does not, then the column should be initially included.

   <dt id=columnType2>To establish whether the data can be sorted relative to
    a particular column

   <dd>Check whether the <code title=datagrid-column-class-sortable><a
    href="#sortable">sortable</a></code> class applies to the column. If it
    does, then the user should be able to ask the UA to display the data
    sorted by that column; if it does not, then the user agent must not allow
    the user to ask for the data to be sorted by that column.

   <dt>To establish if a column is a sorted column

   <dd>If the user agent can handle multiple columns being marked as sorted
    simultaneously: Check whether the <code
    title=datagrid-column-class-sorted><a href="#sorted">sorted</a></code>
    class applies to the column. If it does, then that column is the sorted
    column, otherwise it is not.

   <dd>If the user agent can only handle one column being marked as sorted at
    a time: Check each column in turn, starting with the first one, to see
    whether the <code title=datagrid-column-class-sorted><a
    href="#sorted">sorted</a></code> class applies to that column. The first
    column that has that class, if any, is the sorted column. If none of the
    columns have that class, there is no sorted column.

   <dt>To establish the sort direction of a sorted column

   <dd>Check whether the <code title=datagrid-column-class-reversed><a
    href="#reversed">reversed</a></code> class applies to the column. If it
    does, then the sort direction is descending (down; first rows have the
    highest values), otherwise it is ascending (up; first rows have the
    lowest values).

   <dt>To determine the total number of rows

   <dd>Determine the number of rows for the root of the data grid, and
    determine the number of child rows for each open row. The total number of
    rows is the sum of all these numbers.

   <dt>To determine the number of rows for the root of the data grid

   <dd>Invoke the <code title=dom-provider-getRowCount><a
    href="#getrowcount">getRowCount()</a></code> method with a <code><a
    href="#rowspecification">RowSpecification</a></code> object representing
    the empty path as its only argument. The return value is the number of
    rows at the top level of the data grid. If the return value of the method
    is negative, not an integer, or simply not a numeric type, or if the
    method is not defined, then zero must be used instead.

   <dt>To determine the number of child rows for a row

   <dd>Invoke the <code title=dom-provider-getRowCount><a
    href="#getrowcount">getRowCount()</a></code> method with a <code><a
    href="#rowspecification">RowSpecification</a></code> object representing
    the path to the row in question. The return value is the number of child
    rows for the given row. If the return value of the method is negative,
    not an integer, or simply not a numeric type, or if the method is not
    defined, then zero must be used instead.

   <dt>To determine what order to render rows in

   <dd>
    <p>Invoke the <code title=dom-provider-getChildAtPosition><a
     href="#getchildatposition">getChildAtPosition()</a></code> method with a
     <code><a href="#rowspecification">RowSpecification</a></code> object
     representing the path to the parent of the rows that are being rendered
     as the first argument, and the position that is being rendered as the
     second argument. The return value is the index of the row to render in
     that position.</p>

    <div class=example>
     <p>If the rows are:</p>

     <ol>
      <li> Row "0"
       <ol>
        <li> Row "0,0"

        <li> Row "0,1"
       </ol>

      <li> Row "1"
       <ol>
        <li> Row "1,0"

        <li> Row "1,1"
       </ol>
     </ol>

     <p>...and the <code title=dom-provider-getChildAtPosition><a
      href="#getchildatposition">getChildAtPosition()</a></code> method is
      implemented as follows:</p>

     <pre>function getChildAtPosition(parent, child) {
  // always return the reverse order
  return getRowCount(parent)-child-1;
}</pre>

     <p>...then the rendering would actually be:</p>

     <ol>
      <li> Row "1"
       <ol>
        <li> Row "1,1"

        <li> Row "1,0"
       </ol>

      <li> Row "0"
       <ol>
        <li> Row "0,1"

        <li> Row "0,0"
       </ol>
     </ol>
    </div>

    <p>If the return value of the method is negative, larger than the number
     of rows that the <code title=dom-provider-getRowCount><a
     href="#getrowcount">getRowCount()</a></code> method reported for that
     parent, not an integer, or simply not a numeric type, then the entire
     data grid should be disabled. Similarly, if the method returns the same
     value for two or more different values for the second argument (with the
     same first argument, and assuming that the data grid hasn't had relevant
     update methods invoked in the meantime), then the data grid should be
     disabled. Instead of disabling the data grid, the user agent may act as
     if the <code title=dom-provider-getChildAtPosition><a
     href="#getchildatposition">getChildAtPosition()</a></code> method was
     not defined on the data provider (thus disabling sorting for that data
     grid, but still letting the user interact with the data). If the method
     is not defined, then the return value must be assumed to be the same as
     the second argument (an indentity transform; the data is rendered in its
     natural order).</p>

   <dt>To establish what classes apply to a row

   <dd>Invoke the <code title=dom-provider-getRowClasses><a
    href="#getrowclasses">getRowClasses()</a></code> method with a <code><a
    href="#rowspecification">RowSpecification</a></code> object representing
    the row in question, and a <code><a
    href="#domtokenlist0">DOMTokenList</a></code> associated with an empty
    string. The tokens contained in the <code><a
    href="#domtokenlist0">DOMTokenList</a></code> object's underlying string
    when the method returns represent the classes that apply to the row in
    question. If the method is not defined, no classes apply to the row.

   <dt>To establish whether a row is a data row or a special row

   <dd>Examine the classes that apply to the row. If the <code
    title=datagrid-row-class-header><a href="#header0">header</a></code>
    class applies to the row, then it is not a data row, it is a subheading.
    The data from the first cell of the row is the text of the subheading,
    the rest of the cells must be ignored. Otherwise, if the <code
    title=datagrid-row-class-separator><a
    href="#separator">separator</a></code> class applies to the row, then in
    the place of the row, a separator should be shown. Otherwise, if the
    <code title=datagrid-row-class-selectable-separator><a
    href="#selectable-separator">selectable-separator</a></code> class
    applies to the row, then the row should be a data row, but represented as
    a separator. (The difference between a <code
    title=datagrid-row-class-separator><a
    href="#separator">separator</a></code> and a <code
    title=datagrid-row-class-selectable-separator><a
    href="#selectable-separator">selectable-separator</a></code> is that the
    former is not an item that can be actually selected, whereas the second
    can be selected and thus has a context menu that applies to it, and so
    forth.) For both kinds of separator rows, the data of the rows' cells
    must all be ignored. If none of those three classes apply then the row is
    a simple data row.

   <dt id=rowType1>To establish whether a row is openable

   <dd>Determine the number of child rows for that row. If there are one or
    more child rows, then the row is openable.

   <dt>To establish whether a row should be initially open or closed

   <dd>If <a href="#rowType1">the row is openable</a>, examine the classes
    that apply to the row. If the <code
    title=datagrid-row-class-initially-open><a
    href="#initially-open">initially-open</a></code> class applies to the
    row, then it should be initially open. Otherwise, if the <code
    title=datagrid-row-class-initially-closed><a
    href="#initially-closed">initially-closed</a></code> class applies to the
    row, then it must be initially closed. Otherwise, if neither class
    applies to the row, or if the row is not openable, then the initial state
    of the row is entirely up to the UA.</dd>
   <!-- XXXPA
   <dt>To establish whether a row is deletable</dt>

   <dd>Check whether the <code
   title="datagrid-row-class-deletable">deletable</code> class applies
   to the row. If it does, the row is deletable, and interactive user
   agents should provide a way for the user to request that the row be
   deleted. (See the <code
   title="dom-provider-performActionOnRow">performActionOnRow()</code>
   method for more details.) Otherwise, the user agent should not
   provide the user with a method for requesting that the row be
   deleted.</dd>
-->

   <dt>To obtain a URI to an image representing a row

   <dd>Invoke the <code title=dom-provider-getRowImage><a
    href="#getrowimage">getRowImage()</a></code> method with a <code><a
    href="#rowspecification">RowSpecification</a></code> object representing
    the row in question. The return value is a string representing a URI (or
    IRI) to an image. Relative URIs must be interpreted relative to the
    <code><a href="#datagrid0">datagrid</a></code>'s base URI. If the method
    returns the empty string, null, or if the method is not defined, then the
    row has no associated image.

   <dt>To obtain a context menu appropriate for a particular row

   <dd>Invoke the <code title=dom-provider-getRowMenu><a
    href="#getrowmenu">getRowMenu()</a></code> method with a <code><a
    href="#rowspecification">RowSpecification</a></code> object representing
    the row in question. The return value is a reference to an object
    implementing the <code><a
    href="#htmlmenuelement">HTMLMenuElement</a></code> interface, i.e. a
    <code><a href="#menu">menu</a></code> element DOM node. (This element
    must then be interpreted as described in the section on context menus to
    obtain the actual context menu to use.<!-- XXXX update once menu section
   works; with xrefs -->)
    If the method returns something that is not an <code><a
    href="#htmlmenuelement">HTMLMenuElement</a></code>, or if the method is
    not defined, then the row has no associated context menu. User agents may
    provide their own default context menu, and may add items to the
    author-provided context menu. For example, such a menu could allow the
    user to change the presentation of the <code><a
    href="#datagrid0">datagrid</a></code> element.

   <dt>To establish the value of a particular cell

   <dd>Invoke the <code title=dom-provider-getCellData><a
    href="#getcelldata">getCellData()</a></code> method with the first
    argument being a <code><a
    href="#rowspecification">RowSpecification</a></code> object representing
    the row of the cell in question and the second argument being the index
    of the cell's column. The second argument must be a non-negative integer
    less than the total number of columns. The return value is the value of
    the cell. If the return value is null or the empty string, or if the
    method is not defined, then the cell has no data. (For progress bar
    cells, the cell's value must be further interpreted, as described below.)

   <dt>To establish what classes apply to a cell

   <dd>Invoke the <code title=dom-provider-getCellClasses><a
    href="#getcellclasses">getCellClasses()</a></code> method with the first
    argument being a <code><a
    href="#rowspecification">RowSpecification</a></code> object representing
    the row of the cell in question, the second argument being the index of
    the cell's column, and the third being an object implementing the
    <code><a href="#domtokenlist0">DOMTokenList</a></code> interface,
    associated with an empty string. The second argument must be a
    non-negative integer less than the total number of columns. The tokens
    contained in the <code><a href="#domtokenlist0">DOMTokenList</a></code>
    object's underlying string when the method returns represent the classes
    that apply to that cell. If the method is not defined, no classes apply
    to the cell.

   <dt id=cellType1>To establish how the type of a cell

   <dd>Examine the classes that apply to the cell. If the <code
    title=datagrid-cell-class-progress><a
    href="#progress1">progress</a></code> class applies to the cell, it is a
    progress bar. Otherwise, if the <code
    title=datagrid-cell-class-cyclable><a
    href="#cyclable">cyclable</a></code> class applies to the cell, it is a
    cycling cell whose value can be cycled between multiple states.
    Otherwise, none of these classes apply, and the cell is a simple text
    cell.

   <dt>To establish the value of a progress bar cell

   <dd>If the value <var title="">x</var> of the cell is a string that can be
    <a href="#rules1" title="rules for parsing floating point number
    values">converted to a floating-point number</a> in the range
    0.0&nbsp;&le;&nbsp;<var title="">x</var>&nbsp;&le;&nbsp;1.0, then the
    progress bar has that value (0.0 means no progress, 1.0 means complete).
    Otherwise, the progress bar is an indeterminate progress bar.

   <dt id=cellType2>To establish how a simple text cell should be presented

   <dd>Check whether one of the <code title=datagrid-cell-class-checked><a
    href="#checked">checked</a></code>, <code
    title=datagrid-cell-class-unchecked><a
    href="#unchecked">unchecked</a></code>, or <code
    title=datagrid-cell-class-indeterminate><a
    href="#indeterminate">indeterminate</a></code> classes applies to the
    cell. If any of these are present, then the cell has a checkbox,
    otherwise none are present and the cell does not have a checkbox. If the
    cell has no checkbox, check whether the <code
    title=datagrid-cell-class-editable><a
    href="#editable">editable</a></code> class applies to the cell. If it
    does, then the cell value is editable, otherwise the cell value is
    static.

   <dt>To establish the state of a cell's checkbox, if it has one

   <dd>Check whether the <code title=datagrid-cell-class-checked><a
    href="#checked">checked</a></code> class applies to the cell. If it does,
    the cell is checked. Otherwise, check whether the <code
    title=datagrid-cell-class-unchecked><a
    href="#unchecked">unchecked</a></code> class applies to the cell. If it
    does, the cell is unchecked. Otherwise, the <code
    title=datagrid-cell-class-indeterminate><a
    href="#indeterminate">indeterminate</a></code> class appplies to the cell
    and the cell's checkbox is in an indeterminate state. When the <code
    title=datagrid-cell-class-indeterminate><a
    href="#indeterminate">indeterminate</a></code> class appplies to the
    cell, the checkbox is a tristate checkbox, and the user can set it to the
    indeterminate state. Otherwise, only the <code
    title=datagrid-cell-class-checked><a href="#checked">checked</a></code>
    and/or <code title=datagrid-cell-class-unchecked><a
    href="#unchecked">unchecked</a></code> classes apply to the cell, and the
    cell can only be toggled betwen those two states.
  </dl>

  <p>If the data provider ever raises an exception while the <code><a
   href="#datagrid0">datagrid</a></code> is invoking one of its methods, the
   <code><a href="#datagrid0">datagrid</a></code> must act, for the purposes
   of that particular method call, as if the relevant method had not been
   defined.

  <p>A <code><a href="#rowspecification">RowSpecification</a></code> object
   <var title="">p</var> with <var title="">n</var> path components passed to
   a method of the data provider must fulfill the constraint
   <span>0&nbsp;&le;&nbsp;<var title="">p<sub title=""><var
   title="">i</var></sub></var>&nbsp;&lt;&nbsp;<var title="">m</var>-1</span>
   for all integer values of <var title="">i</var> in the range
   <span>0&nbsp;&le;&nbsp;<var title="">i</var>&nbsp;&lt;&nbsp;<var
   title="">n</var>-1</span>, where <var title="">m</var> is the value that
   was last returned by the <code title=dom-provider-getRowCount><a
   href="#getrowcount">getRowCount()</a></code> method when it was passed the
   <code><a href="#rowspecification">RowSpecification</a></code> object <var
   title="">q</var> with <span><var title="">i</var>-1</span> items, where
   <span><var title="">p<sub title=""><var
   title="">i</var></sub></var>&nbsp;=&nbsp;<var title="">q<sub title=""><var
   title="">i</var></sub></var></span> for all integer values of <var
   title="">i</var> in the range <span>0&nbsp;&le;&nbsp;<var
   title="">i</var>&nbsp;&lt;&nbsp;<var title="">n</var>-1</span>, with any
   changes implied by the update methods taken into account.

  <p id=inconsistentDataProvider>The data model is considered stable: user
   agents may assume that subsequent calls to the data provider methods will
   return the same data, until one of the update methods is called on the
   <code><a href="#datagrid0">datagrid</a></code> element. If a user agent is
   returned inconsistent data, for example if the number of rows returned by
   <code title=dom-provider-getRowCount><a
   href="#getrowcount">getRowCount()</a></code> varies in ways that do not
   match the calls made to the update methods, the user agent may disable the
   <code><a href="#datagrid0">datagrid</a></code>. User agents that do not
   disable the <code><a href="#datagrid0">datagrid</a></code> in inconsistent
   cases must honour the most recently returned values.

  <p>User agents may cache returned values so that the data provider is never
   asked for data that could contradict earlier data. User agents must not
   cache the return value of the <code title=dom-provider-getRowMenu><a
   href="#getrowmenu">getRowMenu</a></code> method.

  <p>The exact algorithm used to populate the data grid is not defined here,
   since it will differ based on the presentation used. However, the
   behaviour of user agents must be consistent with the descriptions above.
   For example, it would be non-conformant for a user agent to make cells
   have both a checkbox and be editable, as the descriptions above state that
   cells that have a checkbox cannot be edited.</p>
  <!-- XXX speaking of which, do we actually want that
  limitation? -->

  <h5 id=updating><span class=secno>3.18.2.6. </span>Updating the <code><a
   href="#datagrid0">datagrid</a></code></h5>

  <p>Whenever the <code title=dom-datagrid-data><a
   href="#data2">data</a></code> attribute is set to a new value, the
   <code><a href="#datagrid0">datagrid</a></code> must clear the current
   selection, remove all the displayed rows, and plan to repopulate itself
   using the information from the new data provider at the earliest
   opportunity.

  <p>There are a number of update methods that can be invoked on the <code><a
   href="#datagrid0">datagrid</a></code> element to cause it to refresh
   itself in slightly less drastic ways:

  <p>When the <dfn id=updateeverything
   title=dom-datagrid-updateEverything><code>updateEverything()</code></dfn>
   method is called, the user agent must repopulate the entire <code><a
   href="#datagrid0">datagrid</a></code>. If the number of rows decreased,
   the selection must be updated appropriately. If the number of rows
   increased, the new rows should be left unselected.

  <p>When the <dfn id=updaterowschanged
   title=dom-datagrid-updateRowsChanged><code>updateRowsChanged(<var
   title="">row</var>, <var title="">count</var>)</code></dfn> method is
   called, the user agent must refresh the rendering of the rows starting
   from the row specified by <var title="">row</var>, and including the <var
   title="">count</var> next siblings of the row (or as many next siblings as
   it has, if that is less than <var title="">count</var>), including all
   descendant rows.

  <p>When the <dfn id=updaterowsinserted
   title=dom-datagrid-updateRowsInserted><code>updateRowsInserted(<var
   title="">row</var>, <var title="">count</var>)</code></dfn> method is
   called, the user agent must assume that <var title="">count</var> new rows
   have been inserted, such that the first new row is indentified by <var
   title="">row</var>. The user agent must update its rendering and the
   selection accordingly. The new rows should not be selected.

  <p>When the <dfn id=updaterowsremoved
   title=dom-datagrid-updateRowsRemoved><code>updateRowsRemoved(<var
   title="">row</var>, <var title="">count</var>)</code></dfn> method is
   called, the user agent must assume that <var title="">count</var> rows
   have been removed starting from the row that used to be identifier by <var
   title="">row</var>. The user agent must update its rendering and the
   selection accordingly.

  <p>The <dfn id=updaterowchanged
   title=dom-datagrid-updateRowChanged><code>updateRowChanged(<var
   title="">row</var>)</code></dfn> method must be exactly equivalent to
   calling <code title=dom-datagrid-updateRowsChanged><a
   href="#updaterowschanged">updateRowsChanged(<var title="">row</var>,
   1)</a></code>.

  <p>When the <dfn id=updatecolumnchanged
   title=dom-datagrid-updateColumnChanged><code>updateColumnChanged(<var
   title="">column</var>)</code></dfn> method is called, the user agent must
   refresh the rendering of the specified column <var title="">column</var>,
   for all rows.

  <p>When the <dfn id=updatecellchanged
   title=dom-datagrid-updateCellChanged><code>updateCellChanged(<var
   title="">row</var>, <var title="">column</var>)</code></dfn> method is
   called, the user agent must refresh the rendering of the cell on row <var
   title="">row</var>, in column <var title="">column</var>.

  <p>Any effects the update methods have on the <code><a
   href="#datagrid0">datagrid</a></code>'s selection is not considered a
   change to the selection, and must therefore not fire the <code
   title=event-select><a href="#select">select</a></code> event.

  <p>These update methods should only be called by the data provider, or code
   acting on behalf of the data provider. In particular, calling the <code
   title=dom-datagrid-updateRowsInserted><a
   href="#updaterowsinserted">updateRowsInserted()</a></code> and <code
   title=dom-datagrid-updateRowsRemoved><a
   href="#updaterowsremoved">updateRowsRemoved()</a></code> methods without
   actually inserting or removing rows from the data provider is <a
   href="#inconsistentDataProvider">likely to result in inconsistent
   renderings</a>, and the user agent is likely to disable the data grid.

  <h5 id=requirements><span class=secno>3.18.2.7. </span>Requirements for
   interactive user agents</h5>

  <p><em>This section only applies to interactive user agents.</em>

  <p>If the <code><a href="#datagrid0">datagrid</a></code> element has a <dfn
   id=disabled3 title=attr-datagrid-disabled><code>disabled</code></dfn>
   attribute, then the user agent must disable the <code><a
   href="#datagrid0">datagrid</a></code>, preventing the user from
   interacting with it. The <code><a href="#datagrid0">datagrid</a></code>
   element should still continue to update itself when the data provider
   signals changes to the data, though. Obviously, conformance requirements
   stating that <code><a href="#datagrid0">datagrid</a></code> elements must
   react to users in particular ways do not apply when one is disabled.

  <p>If <a href="#rowType1">a row is openable</a>, then the user should be
   able to toggle its open/closed state. When a row's open/closed state
   changes, the user agent must update the rendering to match the new state.

  <p>If a cell is a cell whose value <a href="#cellType1">can be cycled
   between multiple states</a>, then the user must be able to activate the
   cell to cycle its value. When the user activates this "cycling" behaviour
   of a cell, then the <code><a href="#datagrid0">datagrid</a></code> must
   invoke the data provider's <code title=dom-provider-cycleCell><a
   href="#cyclecell">cycleCell()</a></code> method, with a <code><a
   href="#rowspecification">RowSpecification</a></code> object representing
   the cell's row as the first argument and the cell's column index as the
   second. The <code><a href="#datagrid0">datagrid</a></code> must act as if
   the <code><a href="#datagrid0">datagrid</a></code>'s <code
   title=dom-datagrid-updateCellChanged><a
   href="#updatecellchanged">updateCellChanged()</a></code> method had been
   invoked with those same arguments immediately before the provider's method
   was invoked.

  <p>When a cell <a href="#cellType2">has a checkbox</a>, the user must be
   able to set the checkbox's state. When the user changes the state of a
   checkbox in such a cell, the <code><a
   href="#datagrid0">datagrid</a></code> must invoke the data provider's
   <code title=dom-provider-setCellCheckedState><a
   href="#setcellcheckedstate">setCellCheckedState()</a></code> method, with
   a <code><a href="#rowspecification">RowSpecification</a></code> object
   representing the cell's row as the first argument, the cell's column index
   as the second, and the checkbox's new state as the third. The state should
   be represented by the number 1 if the new state is checked, 0 if the new
   state is unchecked, and -1 if the new state is indeterminate (which must
   only be possible if the cell has the <code
   title=datagrid-cell-class-indeterminate><a
   href="#indeterminate">indeterminate</a></code> class set). The <code><a
   href="#datagrid0">datagrid</a></code> must act as if the <code><a
   href="#datagrid0">datagrid</a></code>'s <code
   title=dom-datagrid-updateCellChanged><a
   href="#updatecellchanged">updateCellChanged()</a></code> method had been
   invoked, specifying the same cell, immediately before the provider's
   method was invoked.

  <p>If a cell <a href="#cellType2">is editable</a>, the user must be able to
   edit the data for that cell, and doing so must cause the user agent to
   invoke the <code title=dom-provider-editCell><a
   href="#editcell">editCell()</a></code> method of the data provider with
   three arguments: a <code><a
   href="#rowspecification">RowSpecification</a></code> object representing
   the cell's row, the cell's column's index, and the new text entered by the
   user. The user agent must act as if the <code
   title=dom-datagrid-updateCellChanged><a
   href="#updatecellchanged">updateCellChanged()</a></code> method had been
   invoked, with the same row and column specified, immediately before the
   provider's method was invoked.</p>
  <!-- XXXPA <p class="big-issue">define actions (performAction(), etc)</p> -->

  <h5 id=the-selection><span class=secno>3.18.2.8. </span>The selection</h5>

  <p><em>This section only applies to interactive user agents. For other user
   agents, the <code title=dom-datagrid-selection><a
   href="#selection0">selection</a></code> attribute must return null.</em>

  <pre
   class=idl>interface <dfn id=datagridselection>DataGridSelection</dfn> {
  readonly attribute unsigned long <span title=dom-DataGridSelection-count>length</span>;
  <a href="#rowspecification">RowSpecification</a> <span title=dom-DataGridSelection->item</span>(in unsigned long index);
  boolean <a href="#isselected" title=dom-DataGridSelection-isSelected>isSelected</a>(in <a href="#rowspecification">RowSpecification</a> row);
  void <a href="#setselected" title=dom-DataGridSelection-setSelected>setSelected</a>(in <a href="#rowspecification">RowSpecification</a> row, in boolean selected);
<!--  void <span title="dom-DataGridSelection-addRange">addRange</span>(in <span>RowSpecification</span> first, in <span>RowSpecification</span> last);
  void <span title="dom-DataGridSelection-removeRange">removeRange</span>(in <span>RowSpecification</span> first, in <span>RowSpecification</span> last);
XXX selection ranges -->
  void <a href="#selectall" title=dom-DataGridSelection-selectAll>selectAll</a>();
  void <a href="#invert" title=dom-DataGridSelection-invert>invert</a>();
  void <a href="#clear" title=dom-DataGridSelection-clear>clear</a>();
};</pre>

  <p>Each <code><a href="#datagrid0">datagrid</a></code> element must keep
   track of which rows are currently selected. Initially no rows are
   selected, but this can be changed via the methods described in this
   section. <!--XXX
  select-provider-selection The default data provider, for instance,
  changes which rows are selected when it is first initialised.-->

  <p>The selection of a <code><a href="#datagrid0">datagrid</a></code> is
   represented by its <dfn id=selection0
   title=dom-datagrid-selection><code>selection</code></dfn> DOM attribute,
   which must be a <code><a
   href="#datagridselection">DataGridSelection</a></code> object.

  <p><code><a href="#datagridselection">DataGridSelection</a></code> objects
   represent the rows in the selection. In the selection the rows must be
   ordered in the natural order of the data provider (and not, e.g., the
   rendered order). Rows that are not rendered because one of their ancestors
   is closed must share the same selection state as their nearest rendered
   ancestor. Such rows are not considered part of the selection for the
   purposes of iterating over the selection.

  <p class=note>This selection API doesn't allow for hidden rows to be
   selected because it is trivial to create a data provider that has infinite
   depth, which would then require the selection to be infinite if every row,
   including every hidden row, was selected.

  <p>The <dfn id=length4
   title=dom-DataGridSelection-length><code>length</code></dfn> attribute
   must return the number of rows currently present in the selection. The
   <dfn id=itemindex3 title=dom-DataGridSelection-item><code>item(<var
   title="">index</var>)</code></dfn> method must return the <var
   title="">index</var>th row in the selection. If the argument is out of
   range (less than zero or greater than the number of selected rows minus
   one), then it must raise an <code>INDEX_SIZE_ERR</code> exception. <a
   href="#refsDOM3CORE">[DOM3CORE]</a>

  <p>The <dfn id=isselected
   title=dom-DataGridSelection-isSelected><code>isSelected()</code></dfn>
   method must return the selected state of the row specified by its
   argument. If the specified row exists and is selected, it must return
   true, otherwise it must return false.

  <p>The <dfn id=setselected
   title=dom-DataGridSelection-setSelected><code>setSelected()</code></dfn>
   method takes two arguments, <var title="">row</var> and <var
   title="">selected</var>. When invoked, it must set the selection state of
   row <var title="">row</var> to selected if <var title="">selected</var> is
   true, and unselected if it is false. If <var title="">row</var> is not a
   row in the data grid, the method must raise an <code>INDEX_SIZE_ERR</code>
   exception. If the specified row is not rendered because one of its
   ancestors is closed, the method must do nothing.

  <p>The <dfn id=selectall
   title=dom-DataGridSelection-selectAll><code>selectAll()</code></dfn>
   method must mark all the rows in the data grid as selected. After a call
   to <code title=dom-DataGridSelection-selectAll><a
   href="#selectall">selectAll()</a></code>, the <code
   title=dom-DataGridSelection-length><a href="#length4">length</a></code>
   attribute will return the number of rows in the data grid, not counting
   children of closed rows.

  <p>The <dfn id=invert
   title=dom-DataGridSelection-invert><code>invert()</code></dfn> method must
   cause all the rows in the selection that were marked as selected to now be
   marked as not selected, and vice versa.

  <p>The <dfn id=clear
   title=dom-DataGridSelection-clear><code>clear()</code></dfn> method must
   mark all the rows in the data grid to be marked as not selected. After a
   call to <code title=dom-DataGridSelection-clear><a
   href="#clear">clear()</a></code>, the <code
   title=dom-DataGridSelection-length><a href="#length4">length</a></code>
   attribute will return zero.

  <p>If the <code><a href="#datagrid0">datagrid</a></code> element has a <dfn
   id=multiple0 title=attr-datagrid-multiple><code>multiple</code></dfn>
   attribute, then the user must be able to select any number of rows (zero
   or more). If the attribute is not present, then the user must only be able
   to select a single row at a time, and selecting another one must unselect
   all the other rows.

  <p class=note>This only applies to the user. Scripts can select multiple
   rows even when the <code title=attr-datagrid-multiple><a
   href="#multiple0">multiple</a></code> attribute is absent.

  <p>Whenever the selection of a <code><a
   href="#datagrid0">datagrid</a></code> changes, whether due to the user
   interacting with the element, or as a result of calls to methods of the
   <code title=dom-datagrid-selection><a
   href="#selection0">selection</a></code> object, a <dfn id=select
   title=event-select><code>select</code></dfn><!-- XXX check if we
  really should be DFNing this here. It's a DOM3 Core event. What's
  our story going to be regarding events and defining them? -->
   event that bubbles but is not cancelable must be fired on the <code><a
   href="#datagrid0">datagrid</a></code> element. If changes are made to the
   selection via calls to the object's methods during the execution of a
   script<!-- XXX should xref to a better explanation -->, then the <code
   title=event-select><a href="#select">select</a></code> events must be
   coalesced into one, which must then be fired<!--XXX xref again--> when the
   script execution has completed<!-- XXX xref -->.

  <p class=note>The <code><a
   href="#datagridselection">DataGridSelection</a></code> interface has no
   relation to the <code><a href="#selection1">Selection</a></code>
   interface.

  <h5 id=columns><span class=secno>3.18.2.9. </span>Columns and captions</h5>

  <p><em>This section only applies to interactive user agents.</em>

  <p>Each <code><a href="#datagrid0">datagrid</a></code> element must keep
   track of which columns are currently being rendered. User agents should
   initially show all the columns except those with the <code
   title=datagrid-column-class-initially-hidden><a
   href="#initially-hidden">initially-hidden</a></code> class, but may allow
   users to hide or show columns. User agents should initially display the
   columns in the order given by the data provider, but may allow this order
   to be changed by the user.

  <p>If columns are not being used, as might be the case if the data grid is
   being presented in an icon view, or if an overview of data is being read
   in an aural context, then the text of the first column of each row should
   be used to represent the row.

  <p>If none of the columns have any captions (i.e. if the data provider does
   not provide a <code title=dom-provider-getCaptionText><a
   href="#getcaptiontext">getCaptionText()</a></code> method), then user
   agents may avoid showing the column headers at all. This may prevent the
   user from performing actions on the columns (such as reordering them,
   changing the sort column, and so on).

  <p class=note>Whatever the order used for rendering, and irrespective of
   what columns are being shown or hidden, the "first column" as referred to
   in this specification is always the column with index zero, and the "last
   column" is always the column with the index one less than the value
   returned by the <code title=dom-provider-getcolumnCount><a
   href="#getcolumncount">getColumnCount()</a></code> method of the data
   provider.

  <p>If <a href="#columnType2">a column is sortable</a>, then the user must
   be able to invoke it to sort the data. When the user does so, then the
   <code><a href="#datagrid0">datagrid</a></code> must invoke the data
   provider's <code title=dom-provider-toggleColumnSortState><a
   href="#togglecolumnsortstate">toggleColumnSortState()</a></code> method,
   with the column's index as the only argument. The <code><a
   href="#datagrid0">datagrid</a></code> must <em>then</em> act as if the
   <code><a href="#datagrid0">datagrid</a></code>'s <code
   title=dom-datagrid-updateEverything><a
   href="#updateeverything">updateEverything()</a></code> method had been
   invoked.</p>
  <!--XXXDND
  <h5>Drag and drop in <code>datagrid</code>s</h5>

  <p><em>This section only applies to interactive user agents.</p>

  <p class="big-issue">define drag and drop in datagrids; selectiondraggable, etc.</p>
-->

  <h4 id=the-command><span class=secno>3.18.3. </span>The <dfn
   id=command0><code>command</code></dfn> element</h4>

  <p><a href="#metadata" title="metadata elements">Metadata element</a>, and
   <a href="#strictly">strictly inline-level content</a>.</p>
  <!-- XXX we sure we
  want it to be metadata? -->

  <dl class=element>
   <dt>Contexts in which this element may be used:

   <dd>In a <code><a href="#head">head</a></code> element.

   <dd>Where <a href="#strictly">strictly inline-level content</a> is
    allowed.

   <dt>Content model:

   <dd>Empty.

   <dt>Element-specific attributes:

   <dd><code title=attr-command-type><a href="#type13">type</a></code>

   <dd><code title=attr-command-label><a href="#label">label</a></code>

   <dd><code title=attr-command-icon><a href="#icon">icon</a></code>

   <dd><code title=attr-command-hidden><a href="#hidden">hidden</a></code>

   <dd><code title=attr-command-disabled><a
    href="#disabled4">disabled</a></code>

   <dd><code title=attr-command-checked><a
    href="#checked0">checked</a></code>

   <dd><code title=attr-command-radiogroup><a
    href="#radiogroup">radiogroup</a></code>

   <dd><code title=attr-command-default><a
    href="#default1">default</a></code>

   <dd>Also, the <code title=attr-command-title><a
    href="#title6">title</a></code> attribute has special semantics on this
    element.

   <dt>DOM interface:

   <dd>
    <pre
     class=idl>interface <dfn id=htmlcommandelement>HTMLCommandElement</dfn> : <a href="#htmlelement">HTMLElement</a> {
           attribute DOMString <a href="#type14" title=dom-command-type>type</a>;
           attribute DOMString <a href="#label0" title=dom-command-label>label</a>;
           attribute DOMString <a href="#icon0" title=dom-command-icon>icon</a>;
           attribute boolean <a href="#hidden0" title=dom-command-hidden>hidden</a>;
           attribute boolean <a href="#disabled5" title=dom-command-disabled>disabled</a>;
           attribute boolean <a href="#checked1" title=dom-command-checked>checked</a>;
           attribute DOMString <a href="#radiogroup0" title=dom-command-radiogroup>radiogroup</a>;
           attribute boolean <a href="#default2" title=dom-command-default>default</a>;
 void <a href="#click0" title=dom-command-click>click</a>(); // shadows <code><a href="#htmlelement">HTMLElement</a></code>.<code title=dom-click><a href="#click">click()</a></code>
};</pre>

    <p>The <code title=command-ro><a href="#command2">Command</a></code>
     interface must also be implemented by this element.</p>
  </dl>

  <p>The <code><a href="#command0">command</a></code> element represents a
   command that the user can invoke.

  <p>The <dfn id=type13 title=attr-command-type><code>type</code></dfn>
   attribute indicates the kind of command: either a normal command with an
   associated action, or a state or option that can be toggled, or a
   selection of one item from a list of items.

  <p>The attribute's value must be either "<code title="">command</code>",
   "<code title="">checkbox</code>", or "<code title="">radio</code>",
   denoting each of these three types of commands respectively. The attribute
   may also be omitted if the element is to represent the first of these
   types, a simple command.

  <p>The <dfn id=label title=attr-command-label><code>label</code></dfn>
   attribute gives the name of the command, as shown to the user.

  <p>The <dfn id=title6 title=attr-command-title><code>title</code></dfn>
   attribute gives a hint describing the command, which might be shown to the
   user to help him.

  <p>The <dfn id=icon title=attr-command-icon><code>icon</code></dfn>
   attribute gives a picture that represents the command. If the attribute is
   specified, the attribute's value must contain a URI (or IRI).

  <p>The <dfn id=hidden title=attr-command-hidden><code>hidden</code></dfn>
   attribute is a <a href="#boolean0">boolean attribute</a> that, if present,
   indicates that the command is not relevant and is to be hidden.

  <p>The <dfn id=disabled4
   title=attr-command-disabled><code>disabled</code></dfn> attribute is a <a
   href="#boolean0">boolean attribute</a> that, if present, indicates that
   the command is not available in the current state.

  <p class=note>The distinction between <a href="#disabled6"
   title=command-facet-DisabledState>Disabled State</a> and <a
   href="#hidden1" title=command-facet-HiddenState>Hidden State</a> is
   subtle. A command should be Disabled if, in the same context, it could be
   enabled if only certain aspects of the situation were changed. A command
   should be marked as Hidden if, in that situation, the command will never
   be enabled. For example, in the context menu for a water faucet, the
   command "open" might be Disabled if the faucet is already open, but the
   command "eat" would be marked Hidden since the faucet could never be
   eaten.

  <p>The <dfn id=checked0
   title=attr-command-checked><code>checked</code></dfn> attribute is a <a
   href="#boolean0">boolean attribute</a> that, if present, indicates that
   the command is selected.

  <p>The <dfn id=radiogroup
   title=attr-command-radiogroup><code>radiogroup</code></dfn> attribute
   gives the name of the group of commands that will be toggled when the
   command itself is toggled, for commands whose <code
   title=attr-command-type><a href="#type13">type</a></code> attribute has
   the value "<code title="">radio</code>". The scope of the name is the
   child list of the parent element.

  <p>If the <code><a href="#command0">command</a></code> element is used when
   <span title="menu generation">generating</span> a <span>context
   menu</span>, then the <dfn id=default1
   title=attr-command-default><code>default</code></dfn> attribute indicates,
   if present, that the command is the one that would have been invoked if
   the user had directly activated the menu's subject instead of using its
   context menu. The <code title=attr-command-default><a
   href="#default1">default</a></code> attribute is a <a
   href="#boolean0">boolean attribute</a>.

  <div class=example>
   <p class=big-issue>Need an example that shows an element that, if
    double-clicked, invokes an action, but that also has a context menu,
    showing the various <code><a href="#command0">command</a></code>
    attributes off, and that has a default command.</p>
  </div>

  <p>The <dfn id=type14 title=dom-command-type><code>type</code></dfn>, <dfn
   id=label0 title=dom-command-label><code>label</code></dfn>, <dfn id=icon0
   title=dom-command-icon><code>icon</code></dfn>, <dfn id=hidden0
   title=dom-command-hidden><code>hidden</code></dfn>, <dfn id=disabled5
   title=dom-command-disabled><code>disabled</code></dfn>, <dfn id=checked1
   title=dom-command-checked><code>checked</code></dfn>, <dfn id=radiogroup0
   title=dom-command-radiogroup><code>radiogroup</code></dfn>, and <dfn
   id=default2 title=dom-command-default><code>default</code></dfn> DOM
   attributes must <a href="#reflect">reflect</a> their respective namesake
   content attributes.

  <p>The <dfn id=click0 title=dom-command-click><code>click()</code></dfn>
   method's behaviour depends on the value of the <code
   title=attr-command-type><a href="#type13">type</a></code> attribute of the
   element, as follows:

  <dl class=switch>
   <dt>If the <code title=attr-command-type><a href="#type13">type</a></code>
    attribute has the value <code title="">checkbox</code>

   <dd>
    <p>If the element has a <code title=attr-command-checked><a
     href="#checked0">checked</a></code> attribute, the UA must remove that
     attribute. Otherwise, the UA must add a <code
     title=attr-command-checked><a href="#checked0">checked</a></code>
     attribute, with the literal value <code title="">checked</code>. The UA
     must then <a href="#firing">fire a <code title="">click</code> event</a>
     at the element.

   <dt>If the <code title=attr-command-type><a href="#type13">type</a></code>
    attribute has the value <code title="">radio</code>

   <dd>
    <p>If the element has a parent, then the UA must walk the list of child
     nodes of that parent element, and for each node that is a <code><a
     href="#command0">command</a></code> element, if that element has a <code
     title=attr-command-radiogroup><a
     href="#radiogroup">radiogroup</a></code> attribute whose value exactly
     matches the current element's (treating missing <code
     title=attr-command-radiogroup><a
     href="#radiogroup">radiogroup</a></code> attributes as if they were the
     empty string), and has a <code title=attr-command-checked><a
     href="#checked0">checked</a></code> attribute, must remove that
     attribute and <a href="#firing">fire a <code title="">click</code>
     event</a> at the element.</p>

    <p>Then, the element's <code title=attr-command-checked><a
     href="#checked0">checked</a></code> attribute attribute must be set to
     the literal value <code title="">checked</code> and a <span title="file
     a click event"><code title="">click</code> event must be fired</span> at
     the element.

   <dt>Otherwise

   <dd>
    <p>The UA must <a href="#firing">fire a <code title="">click</code>
     event</a> at the element.
  </dl>

  <p class=note>Firing a synthetic <code title=event-click>click</code> event
   at the element does not cause any of the actions described above to
   happen.

  <p class=big-issue> should change all the above so it actually is just
   trigged by a click event, then we could remove the shadowing click()
   method and rely on actual events.

  <p class=big-issue>Need to define the command="" attribute

  <p class=note><code><a href="#command0">command</a></code> elements are not
   rendered unless they <a href="#menu" title=menu>form part of a menu</a>.

  <h4 id=menus><span class=secno>3.18.4. </span>The <dfn
   id=menu><code>menu</code></dfn> element</h4>

  <p><a href="#block-level0" title="block-level elements">Block-level
   element</a>, and <a href="#structured" title="structured inline-level
   elements">structured inline-level element</a>.

  <dl class=element>
   <dt>Contexts in which this element may be used:

   <dd>Where <a href="#block-level0">block-level elements</a> are expected.

   <dd>Where <a href="#structured">structured inline-level elements</a> are
    allowed.

   <dt>Content model:

   <dd>Zero or more <code><a href="#li">li</a></code> elements, or <a
    href="#inline-level0">inline-level content</a> (but not both).

   <dt>Element-specific attributes:

   <dd><code title=attr-menu-type><a href="#type15">type</a></code>

   <dd><code title=attr-menu-label><a href="#label1">label</a></code>

   <dd><code title=attr-menu-autosubmit><a
    href="#autosubmit">autosubmit</a></code>

   <dt>DOM interface:

   <dd>
    <pre
     class=idl>interface <dfn id=htmlmenuelement>HTMLMenuElement</dfn> : <a href="#htmlelement">HTMLElement</a> {
           attribute DOMString <span title=dom-menu-type>type</span>;
           attribute DOMString <span title=dom-menu-label>label</span>;
           attribute boolean <span title=dom-menu-autosubmit>autosubmit</span>;
};</pre>
  </dl>

  <p>The <code><a href="#menu">menu</a></code> element represents a list of
   commands.

  <p>The <dfn id=type15 title=attr-menu-type><code>type</code></dfn>
   attribute is an <a href="#enumerated">enumerated attribute</a> indicating
   the kind of menu being declared. The attribute has three states. The <code
   title=attr-menu-type-context>context</code> keyword maps to the <dfn
   id=context1 title="context menu state">context menu</dfn> state, in which
   the element is declaring a context menu. The <code
   title=attr-menu-type-toolbar>toolbar</code> keyword maps to the <dfn
   id=tool-bar title="tool bar state">tool bar</dfn> state, in which the
   element is declaraing a tool bar. The attribute may also be omitted. The
   <i>missing value default</i> is the <dfn id=list title="list
   state">list</dfn> state, which indicates that the element is merely a list
   of commands that is neither declaring a context menu nor defining a tool
   bar.

  <p>If a <code><a href="#menu">menu</a></code> element's <code
   title=attr-menu-type><a href="#type15">type</a></code> attribute is in the
   <a href="#context1" title="context menu state">context menu</a> state,
   then the element represents the commands of a context menu, and the user
   can only interact with the commands if that context menu is activated.

  <p>If a <code><a href="#menu">menu</a></code> element's <code
   title=attr-menu-type><a href="#type15">type</a></code> attribute is in the
   <a href="#tool-bar" title="tool bar state">tool bar</a> state, then the
   element represents a list of active commands that the user can immediately
   interact with.

  <p>If a <code><a href="#menu">menu</a></code> element's <code
   title=attr-menu-type><a href="#type15">type</a></code> attribute is in the
   <a href="#list" title="list state">list state, then the element either
   represents an unordered list of items (each represented by an
   <code>li</code> element), each of which represents a command that the user
   may perform or activate, or, if the element has no <code>li</code> element
   children, a <span>paragraph</span> describing available commands.</a>

  <p>The <dfn id=label1 title=attr-menu-label><code>label</code></dfn>
   attribute gives the label of the menu. It is used by user agents to
   display nested menus in the UI. For example, a context menu containing
   another menu would use the nested menu's <code title=attr-menu-label><a
   href="#label1">label</a></code> attribute for the submenu's menu label.

  <p>The <dfn id=autosubmit
   title=attr-menu-autosubmit><code>autosubmit</code></dfn> attribute is a <a
   href="#boolean0">boolean attribute</a> that, if present, indicates that
   selections made to form controls in this menu are to result in the
   control's form being immediately submitted.

  <p>If a <code title=event-change>change</code> event bubbles through a
   <code><a href="#menu">menu</a></code> element, then, in addition to any
   other default action that that event might have, the UA must act as if the
   following was an additional default action for that event: if (when it
   comes time to execute the default action) the <code><a
   href="#menu">menu</a></code> element has an <code
   title=attr-menu-autosubmit><a href="#autosubmit">autosubmit</a></code>
   attribute, and the target of the event is an <code>input</code> element,
   and that element has a <code title=attr-input-type>type</code> attribute
   whose value is either <code title="">radio</code> or <code
   title="">checkbox</code>, and the <code>input</code> element in question
   has a non-null <code title=dom-input-form>form</code> DOM attribute, then
   the UA must invoke the <code title=dom-form-submit>submit()</code> method
   of the <code>form</code> element indicated by that DOM attribute.

  <h5 id=menus-intro><span class=secno>3.18.4.1. </span>Introduction</h5>

  <p><em>This section is non-normative.</em>

  <p class=big-issue>...</p>
  <!--


  <pre>&lt;menu type="commands"&gt;
 &lt;li&gt;
  &lt;menu label="File"&gt;
   &lt;button type="button" onclick="fnew()"&gt;New...&lt;/button&gt;
   &lt;button type="button" onclick="fopen()"&gt;Open...&lt;/button&gt;
   &lt;button type="button" onclick="fsave()" id="save"&gt;Save&lt;/button&gt;
   &lt;button type="button" onclick="fsaveas()"&gt;Save as...&lt;/button&gt;
  &lt;/menu&gt;
 &lt;/li&gt;
 &lt;li&gt;
  &lt;menu label="Edit"&gt;
   &lt;button type="button" onclick="ecopy()"&gt;Copy&lt;/button&gt;
   &lt;button type="button" onclick="ecut()"&gt;Cut&lt;/button&gt;
   &lt;button type="button" onclick="epaste()"&gt;Paste&lt;/button&gt;
  &lt;/menu&gt;
 &lt;/li&gt;
 &lt;li&gt;
  &lt;menu label="Help"&gt;
   &lt;li&gt;&lt;a href="help.html"&gt;Help&lt;/a&gt;&lt;/li&gt;
   &lt;li&gt;&lt;a href="about.html"&gt;About&lt;/a&gt;&lt;/li&gt;
  &lt;/menu&gt;
 &lt;/li&gt;
&lt;/menubar&gt;

...

&lt;input command="save"/&gt; &lt;!- - This will act exactly like the
                             Save button above, including reflecting
                             its <code>disabled</code> state dynamically - -&gt;

</pre>

  <p>Here's some markup that falls back on the traditional abuse of
  the <code>select</code> element as a navigation menu, but which is
  implemented as a semi-correct menu using the new techniques of this
  document:</p>

<pre>&lt;form action="redirect.cgi"&gt;
 &lt;menu type="commands"&gt;
  &lt;label for="goto"&gt;Go to...&lt;/label&gt;
  &lt;menu label="Go"&gt;
   &lt;select id="goto"
           onchange="if (this.options[this.selectedIndex].value)
                     window.location = this.options[this.selectedIndex].value"&gt;
    &lt;option value="" selected="selected"&gt; Select site: &lt;/option&gt;
    &lt;option value="http://www.apple.com/"&gt; Apple &lt;/option&gt;
    &lt;option value="http://www.mozilla.org/"&gt; Mozilla &lt;/option&gt;
    &lt;option value="http://www.opera.com/"&gt; Opera &lt;/option&gt;
   &lt;/select&gt;
   &lt;span&gt;&lt;input type="submit" value="Go"&gt;&lt;/span&gt;
  &lt;/menu&gt;
 &lt;/menubar&gt;
&lt;/form&gt;</pre>

<form ...>
 <menu type="toolbar" autosubmit>
  <li>
   <select name="foo" onchange="form.submit()">
     ...
   </select>
   <button>Go</button>
  </li>
  <li>
   <select name="bar" onchange="form.submit()">
     ...
   </select>
   <button>Go</button>
  </li>
 </menu>
</form>

<form ...>
 <menu type="toolbar" autosubmit>
  <menu label="Foo">
   <select name="foo" onchange="form.submit()">
     ...
   </select>
   <button>Go</button>
  </menu>
  <menu label="Bar">
   <select name="bar" onchange="form.submit()">
     ...
   </select>
   <button>Go</button>
  </menu>
 </menu>
</form>

-->

  <h5 id=building><span class=secno>3.18.4.2. </span><dfn
   id=building0>Building menus</dfn></h5>

  <p>A menu consists of a list of zero or more of the following components:

  <ul class=brief>
   <li><a href="#command1" title=concept-command>Commands</a>, which can be
    marked as default commands

   <li>Separators

   <li>Other menus (which allows the list to be nested)
  </ul>

  <p>The list corresponding to a particular <code><a
   href="#menu">menu</a></code> element is built by iterating over its child
   nodes. For each child node in <a href="#tree-order">tree order</a>, the
   required behaviour depends on what the node is, as follows:

  <dl class=switch>
   <dt>An element that <a href="#command1" title=concept-command>defines a
    command</a>

   <dd>Append the command to the menu. If the element is a <code><a
    href="#command0">command</a></code> element with a <code
    title=attr-command-default><a href="#default1">default</a></code>
    attribute, mark the command as being a default command.

   <dt>An <code><a href="#hr">hr</a></code> element

   <dt>An <code>option</code> element that has a <code
    title=attr-option-value>value</code> attribute set to the empty string,
    and has a <code title=attr-option-disabled>disabled</code> attribute, and
    whose <code><a href="#textcontent">textContent</a></code> consists of a
    string of one or more hyphens (U+002D HYPHEN-MINUS)

   <dd>Append a separator to the menu.

   <dt>An <code><a href="#li">li</a></code> element

   <dd>Iterate over the children of the <code><a href="#li">li</a></code>
    element.

   <dt>A <code><a href="#menu">menu</a></code> element with no <code
    title=attr-menu-label><a href="#label1">label</a></code> attribute

   <dt>A <code>select</code> element

   <dd>Append a separator to the menu, then iterate over the children of the
    <code><a href="#menu">menu</a></code> or <code>select</code> element,
    then append another separator.

   <dt>A <code><a href="#menu">menu</a></code> element with a <code
    title=attr-menu-label><a href="#label1">label</a></code> attribute

   <dt>An <code>optgroup</code> element

   <dd>Append a submenu to the menu, using the value of the element's <code
    title="">label</code> attribute as the label of the menu. The submenu
    must be constructed by taking the element and creating a new menu for it
    using the complete process described in this section.

   <dt>Any other node

   <dd><a href="#ignored">Ignore</a> the node.
  </dl>

  <p>Once all the nodes have been processed as described above, the user
   agent must the post-process the menu as follows:

  <ol>
   <li>Any menu item with no label, or whose label is the empty string, must
    be removed.

   <li>Any sequence of two or more separators in a row must be collapsed to a
    single separator.

   <li>Any separator at the start or end of the menu must be removed.
  </ol>

  <h5 id=context><span class=secno>3.18.4.3. </span><dfn id=context2>Context
   menus</dfn></h5>

  <p>The <dfn id=contextmenu
   title=attr-contextmenu><code>contextmenu</code></dfn> attribute gives the
   element's <a href="#context2" title="context menus">context menu</a>. The
   value must be the ID of a <code><a href="#menu">menu</a></code> element in
   the DOM. If the node that would be obtained by the invoking the
   <code>getElementById()</code> method using the attribute's value as the
   only argument is null or not a <code><a href="#menu">menu</a></code>
   element, then the element has no assigned context menu. Otherwise, the
   element's assigned context menu is the element so identified.

  <p>When an element's context menu is requested (e.g. by the user
   right-clicking the element, or pressing a context menu key), the UA must
   <a href="#firing1">fire a <code title="">contextmenu</code> event</a> on
   the element for which the menu was requested.

  <p class=note>Typically, therefore, the firing of the <code
   title=event-contextmenu>contextmenu</code> event will be the default
   action of a <code title=mouseup>mouseup</code> or <code
   title=event-keyup>keyup</code> event. The exact sequence of events is
   UA-dependent, as it will vary based on platform conventions.

  <p>The default action of the <code
   title=event-contextmenu>contextmenu</code> event depends on whether the
   element has a context menu assigned (using the <code
   title=attr-contextmenu><a href="#contextmenu">contextmenu</a></code>
   attribute) or not. If it does not, the default action must be for the user
   agent to show its default context menu, if it has one.

  <p>If the element <em>does</em> have a context menu assigned, then the user
   agent must <a href="#firing3">fire a <code title="">show</code> event</a>
   on the relevant <code><a href="#menu">menu</a></code> element.

  <p>The default action of <em>this</em> event is that the user agent must
   show a context menu <a href="#building0" title="building menus">built</a>
   from the <code><a href="#menu">menu</a></code> element.

  <p>The user agent may also provide access to its default context menu, if
   any, with the context menu shown. For example, it could merge the menu
   items from the two menus together, or provide the page's context menu as a
   submenu of the default menu.

  <p>If the user dismisses the menu without making a selection, nothing in
   particular happens.

  <p>If the user selects a menu item that represents a <span
   title=concept-commands>command</span>, then the UA must invoke that
   command's <a href="#action" title=command-facet-Action>Action</a>.

  <p>Context menus must not, while being shown, reflect changes in the DOM;
   they are constructed as the default action of the <code
   title=event-show>show</code> event and must remain like that until
   dismissed.

  <p>User agents may provide means for bypassing the context menu processing
   model, ensuring that the user can always access the UA's default context
   menus. For example, the user agent could handle right-clicks that have the
   Shift key depressed in such a way that it does not fire the <code
   title=event-contextmenu>contextmenu</code> event and instead always shows
   the default context menu.

  <p>The <dfn id=contextmenu0
   title=dom-contextMenu><code>contextMenu</code></dfn> attribute must <a
   href="#reflect">reflect</a> the <code title=attr-contextmenu><a
   href="#contextmenu">contextmenu</a></code> content attribute.

  <h5 id=toolbars><span class=secno>3.18.4.4. </span><dfn
   id=toolbars0>Toolbars</dfn></h5>

  <p>Toolbars are a kind of menu that is always visible.

  <p>When a <code><a href="#menu">menu</a></code> element has a <code
   title=attr-menu-type><a href="#type15">type</a></code> attribute with the
   value <code title="">toolbar</code>, then the user agent must <a
   href="#building0" title="building menus">build</a> the menu for that
   <code><a href="#menu">menu</a></code> element and <span
   title=render-toolbar>render</span><!-- XXX xref --> it in the document in
   a position appropriate for that <code><a href="#menu">menu</a></code>
   element.

  <p>The user agent must reflect changes made to the <code><a
   href="#menu">menu</a></code>'s DOM immediately in the UI.

  <h4 id=commands><span class=secno>3.18.5. </span>Commands</h4>

  <p>A <dfn id=command1 title=concept-command>command</dfn> is the
   abstraction behind menu items, buttons, and links. Once a command is
   defined, other parts of the interface can refer to the same command,
   allowing many access points to a single feature to share aspects such as
   the disabled state.

  <p id=facets>Commands are defined to have the following <em>facets</em>:

  <dl>
   <dt><dfn id=type16 title=command-facet-Type>Type</dfn>

   <dd>The kind of command: "command", meaning it is a normal command;
    "radio", meaning that triggering the command will, amongst other things,
    set the <a href="#checked2" title=command-facet-CheckedState>Checked
    State</a> to true (and probably uncheck some other commands); or
    "checkbox", meaning that triggering the command will, amongst other
    things, toggle the value of the <a href="#checked2"
    title=command-facet-CheckedState>Checked State</a>.

   <dt><dfn id=id1 title=command-facet-ID>ID</dfn>

   <dd>The name of the command, for referring to the command from the markup
    or from script. If a command has no ID, it is an <dfn
    id=anonymous>anonymous command</dfn>.

   <dt><dfn id=label2 title=command-facet-Label>Label</dfn>

   <dd>The name of the command as seen by the user.

   <dt><dfn id=hint title=command-facet-Hint>Hint</dfn>

   <dd>A helpful or descriptive string that can be shown to the user.

   <dt><dfn id=icon1 title=command-facet-Icon>Icon</dfn>

   <dd>A graphical image that represents the action.

   <dt><dfn id=hidden1 title=command-facet-HiddenState>Hidden State</dfn>

   <dd>Whether the command is hidden or not (basically, whether it should be
    shown in menus).

   <dt><dfn id=disabled6 title=command-facet-DisabledState>Disabled
    State</dfn>

   <dd>Whether the command can be triggered or not. If the <a href="#hidden1"
    title=command-facet-HiddenState>Hidden State</a> is true (hidden) then
    the <a href="#disabled6" title=command-facet-DisabledState>Disabled
    State</a> will be true (disabled) regardless. <span class=issue>We could
    make this into a string value that acts as a Hint for why the command is
    disabled.</span>

   <dt><dfn id=checked2 title=command-facet-CheckedState>Checked State</dfn>

   <dd>Whether the command is checked or not.

   <dt><dfn id=action title=command-facet-Action>Action</dfn>

   <dd>The actual effect that triggering the command will have. This could be
    a scripted event handler, a URI to which to navigate, or a form
    submission.

   <dt><dfn id=triggers title=command-facet-Triggers>Triggers</dfn>

   <dd>The list of elements that can trigger the command. The element
    defining a command is always in the list of elements that can trigger the
    command. For anonymous commands, only the element defining the command is
    on the list, since other elements have no way to refer to it.
  </dl>

  <p>Commands are represented by elements in the DOM. Any element that can
   define a command also implements the <code title=command-ro><a
   href="#command2">Command</a></code> interface:

  <pre
   class=idl>interface <dfn id=command2 title=command-ro>Command</dfn> {<!--
 NOTE: to avoid clashing with the HTMLCommandElement interface's names,
       the members of this interface use cross-references with the title
       dom-command-ro-foo (note the "ro", which stands for "readonly").
-->
  readonly attribute DOMString <a href="#commandtype" title=dom-command-ro-commandType>commandType</a>;          
  readonly attribute DOMString <a href="#id2" title=dom-command-ro-id>id</a>;
  readonly attribute DOMString <a href="#label3" title=dom-command-ro-label>label</a>;
  readonly attribute DOMString <a href="#title7" title=dom-command-ro-title>title</a>;
  readonly attribute DOMString <a href="#icon2" title=dom-command-ro-icon>icon</a>;
  readonly attribute boolean <a href="#hidden2" title=dom-command-ro-hidden>hidden</a>;
  readonly attribute boolean <a href="#disabled7" title=dom-command-ro-disabled>disabled</a>;              
  readonly attribute boolean <a href="#checked3" title=dom-command-ro-checked>checked</a>;              
  void <a href="#click1" title=dom-command-ro-click>click</a>();
  readonly attribute <a href="#htmlcollection0">HTMLCollection</a> <a href="#triggers0" title=dom-command-ro-triggers>triggers</a>;
  readonly attribute <a href="#command0">Command</a> <span title=dom-command-ro-command>command</span>;
};</pre>

  <p>The <code title=command-ro><a href="#command2">Command</a></code>
   interface is implemented by any element capable of defining a command. (If
   an element can define a command, its definition will list this interface
   explicitly.) All the attributes of the <code title=command-ro><a
   href="#command2">Command</a></code> interface are read-only. Elements
   implementing this interface may implement other interfaces that have
   attributes with identical names but that are mutable; in bindings that
   simply flatten all supported interfaces on the object, the mutable
   attributes must shadow the readonly attributes defined in the <code
   title=command-ro><a href="#command2">Command</a></code> interface.

  <p>The <dfn id=commandtype
   title=dom-command-ro-commandType><code>commandType</code></dfn> attribute
   must return a string whose value is either "<code
   title="">command</code>", "<code title="">radio</code>", or "<code
   title="">checked</code>", depending on whether the <a href="#type16"
   title=command-facet-Type>Type</a> of the command defined by the element is
   "command", "radio", or "checked" respectively. If the element does not
   define a command, it must return null.

  <p>The <dfn id=id2 title=dom-command-ro-id><code>id</code></dfn> attribute
   must return the command's <a href="#id1" title=command-facet-ID>ID</a>, or
   null if the element does not define a command or defines an <a
   href="#anonymous">anonymous command</a>. This attribute will be shadowed
   by the <code title=dom-id><a href="#id0">id</a></code> DOM attribute on
   the <code><a href="#htmlelement">HTMLElement</a></code> interface.

  <p>The <dfn id=label3 title=dom-command-ro-label><code>label</code></dfn>
   attribute must return the command's <a href="#label2"
   title=command-facet-Label>Label</a>, or null if the element does not
   define a command or does not specify a <a href="#label2"
   title=command-facet-Label>Label</a>. This attribute will be shadowed by
   the <code title="">label</code> DOM attribute on <code>option</code> and
   <code><a href="#command0">command</a></code> elements.

  <p>The <dfn id=title7 title=dom-command-ro-title><code>title</code></dfn>
   attribute must return the command's <a href="#hint"
   title=command-facet-Hint>Hint</a>, or null if the element does not define
   a command or does not specify a <a href="#hint"
   title=command-facet-Hint>Hint</a>. This attribute will be shadowed by the
   <code title=dom-title><a href="#title0">title</a></code> DOM attribute on
   the <code><a href="#htmlelement">HTMLElement</a></code> interface.

  <p>The <dfn id=icon2 title=dom-command-ro-icon><code>icon</code></dfn>
   attribute must return an absolute URI to the command's <a href="#icon1"
   title=command-facet-Icon>Icon</a>. If the element does not specify an
   icon, or if the element does not define a command, then the attribute must
   return null. This attribute will be shadowed by the <code
   title=dom-command-icon><a href="#icon0">icon</a></code> DOM attribute on
   <code><a href="#command0">command</a></code> elements.

  <p>The <dfn id=hidden2
   title=dom-command-ro-hidden><code>hidden</code></dfn> attribute must
   return true if the command's <a href="#hidden1"
   title=command-facet-HiddenState>Hidden State</a> is that the command is
   hidden, and false if it is that the command is not hidden. If the element
   does not define a command, the attribute must return false. This attribute
   will be shadowed by the <code title=dom-command-hidden><a
   href="#hidden0">hidden</a></code> DOM attribute on <code><a
   href="#command0">command</a></code> elements.

  <p>The <dfn id=disabled7
   title=dom-command-ro-disabled><code>disabled</code></dfn> attribute must
   return true if the command's <a href="#disabled6"
   title=command-facet-DisabledState>Disabled State</a> is that the command
   is disabled, and false if the command is not disabled. This attribute is
   not affected by the command's <a href="#hidden1"
   title=command-facet-HiddenState>Hidden State</a>. If the element does not
   define a command, the attribute must return false. This attribute will be
   shadowed by the <code title="">disabled</code> attribute on
   <code>button</code>, <code>input</code>, <code>option</code>, and <code><a
   href="#command0">command</a></code> elements.

  <p>The <dfn id=checked3
   title=dom-command-ro-checked><code>checked</code></dfn> attribute must
   return true if the command's <a href="#checked2"
   title=command-facet-CheckedState>Checked State</a> is that the command is
   checked, and false if it is that the command is not checked. If the
   element does not define a command, the attribute must return false. This
   attribute will be shadowed by the <code title="">checked</code> attribute
   on <code>input</code> and <code><a href="#command0">command</a></code>
   elements.

  <p>The <dfn id=click1 title=dom-command-ro-click><code>click()</code></dfn>
   method must trigger the <a href="#action"
   title=command-facet-Action>Action</a> for the command. If the element does
   not define a command, this method must do nothing. This method will be
   shadowed by the <code title=dom-click><a href="#click">click()</a></code>
   method on HTML elements, and is included only for completeness.

  <p>The <dfn id=triggers0
   title=dom-command-ro-triggers><code>triggers</code></dfn> attribute must
   return a list containing the elements that can trigger the command (the
   command's <a href="#triggers" title=command-facet-Triggers>Triggers</a>).
   The list must be <a href="#live">live</a>. While the element does not
   define a command, the list must be empty.

  <p>The <dfn id=commands0
   title=dom-document-commands><code>commands</code></dfn> attribute of the
   document's <code><a href="#htmldocument">HTMLDocument</a></code> interface
   must return an <code><a href="#htmlcollection0">HTMLCollection</a></code>
   rooted at the <code>Document</code> node, whose filter matches only
   elements that define commands and have IDs.

  <p>The following elements can define commands: <code title=a-command><a
   href="#using4">a</a></code>, <code title=button-command><a
   href="#using5">button</a></code>, <code title=input-command><a
   href="#using6">input</a></code>, <code title=option-command><a
   href="#using7">option</a></code>, <code title=command-element><a
   href="#command3">command</a></code>.

  <h5 id=using><span class=secno>3.18.5.1. </span><dfn id=using4
   title=a-command>Using the <code>a</code> element to define a command</dfn></h5>

  <p>An <code><a href="#a">a</a></code> element with an <code
   title=attr-hyperlink-href><a href="#href6">href</a></code> attribute <a
   href="#command1" title=concept-command>defines a command</a>.

  <p>The <a href="#type16" title=command-facet-Type>Type</a> of the command
   is "command".

  <p>The <a href="#id1" title=command-facet-ID>ID</a> of the command is the
   value of the <code title=attr-id><a href="#id">id</a></code> attribute of
   the element, if the attribute is present and not empty. Otherwise the
   command is an <a href="#anonymous">anonymous command</a>.

  <p>The <a href="#label2" title=command-facet-Label>Label</a> of the command
   is the string given by the element's <code><a
   href="#textcontent">textContent</a></code> DOM attribute.

  <p>The <a href="#hint" title=command-facet-Hint>Hint</a> of the command is
   the value of the <code title=attr-title><a href="#title">title</a></code>
   attribute of the <code><a href="#a">a</a></code> element. If the attribute
   is not present, the <a href="#hint" title=command-facet-Hint>Hint</a> is
   the empty string.

  <p>The <a href="#icon1" title=command-facet-Icon>Icon</a> of the command is
   the absolute URI of the first image in the element. Specifically, in a
   depth-first search of the children of the element, the first element that
   is <!--either an--> <code><a href="#img">img</a></code> element with a
   <code>src</code> attribute<!--, or an <code>object</code> element
  with a <code>data</code> attribute, or, if the UA supports SVG, an
  <code>svg</code> element in the SVG namespace with a valid <code
  title="">id</code> attribute,-->
   is the one that is used as the image.
   <!--If it is an <code>img</code> element then--> The URI must be taken
   from the element's <code>src</code> attribute. <!--If it is
  an <code>object</code> element then the URI is taken from the
  <code>data</code> attribute. -->
   Relative URIs must be resolved relative to the base URI of the image
   element. <!-- If it is an
  <code>svg</code> element then the URI is formed by taking the URI of
  the document and appending a "#" (U+0023 NUMBER SIGN) and the ID of
  the element.-->
   If no image is found, then the Icon facet is left blank.

  <p>The <a href="#hidden1" title=command-facet-HiddenState>Hidden State</a>
   and <a href="#disabled6" title=command-facet-DisabledState>Disabled
   State</a> facets of the command are always false. (The command is always
   enabled.)

  <p>The <a href="#checked2" title=command-facet-CheckedState>Checked
   State</a> of the command is always false. (The command is never checked.)

  <p>The <a href="#action" title=command-facet-Action>Action</a> of the
   command is to <a href="#firing" title="fire a click event">fire a <code
   title="">click</code> event</a> at the element.

  <h5 id=using0><span class=secno>3.18.5.2. </span><dfn id=using5
   title=button-command>Using the <code>button</code> element to define a
   command</dfn></h5>

  <p>A <code>button</code> element always <a href="#command1"
   title=concept-command>defines a command</a>.

  <p>The <a href="#type16" title=command-facet-Type>Type</a>, <a href="#id1"
   title=command-facet-ID>ID</a>, <a href="#label2"
   title=command-facet-Label>Label</a>, <a href="#hint"
   title=command-facet-Hint>Hint</a>, <a href="#icon1"
   title=command-facet-Icon>Icon</a>, <a href="#hidden1"
   title=command-facet-HiddenState>Hidden State</a>, <a href="#checked2"
   title=command-facet-CheckedState>Checked State</a>, and <a href="#action"
   title=command-facet-Action>Action</a> facets of the command are determined
   <a href="#using4" title=a-command>as for <code>a</code> elements</a> (see
   the previous section).

  <p>The <a href="#disabled6" title=command-facet-DisabledState>Disabled
   State</a> of the command mirrors the disabled state of the button.
   Typically this is given by the element's <code
   title=attr-button-disabled>disabled</code> attribute, but certain button
   types become disabled at other times too (for example, the
   <code>move-up</code> button type is disabled when it would have no
   effect).

  <h5 id=using1><span class=secno>3.18.5.3. </span><dfn id=using6
   title=input-command>Using the <code>input</code> element to define a
   command</dfn></h5>

  <p>An <code>input</code> element whose <code
   title=attr-input-type>type</code> attribute is one of <code>submit</code>,
   <code>reset</code>, <code>button</code>, <code>radio</code>,
   <code>checkbox</code>, <code>move-up</code>, <code>move-down</code>,
   <code>add</code>, and <code>remove</code> <a href="#command1"
   title=concept-command>defines a command</a>.

  <p>The <a href="#type16" title=command-facet-Type>Type</a> of the command
   is "radio" if the <code title=attr-input-type>type</code> attribute has
   the value <code>radio</code>, "checkbox" if the <code>type</code>
   attribute has the value <code>checkbox</code>, and "command" otherwise.

  <p>The <a href="#id1" title=command-facet-ID>ID</a> of the command is the
   value of the <code title=attr-id><a href="#id">id</a></code> attribute of
   the element, if the attribute is present and not empty. Otherwise the
   command is an <a href="#anonymous">anonymous command</a>.

  <p>The <a href="#label2" title=command-facet-Label>Label</a> of the command
   depends on the Type of the command:

  <p>If the <a href="#type16" title=command-facet-Type>Type</a> is "command",
   then it is the string given by the <code
   title=attr-input-value>value</code> attribute, if any, and a
   <span>UA-dependent value</span><!-- XXX xref--> that the UA uses to label
   the button itself if the attribute is absent.

  <p>Otherwise, the <a href="#type16" title=command-facet-Type>Type</a> is
   "radio" or "checkbox". If the element has a <code>label</code> element
   associated with it, the <code><a
   href="#textcontent">textContent</a></code> of the first such element is
   the <a href="#label2" title=command-facet-Label>Label</a> (in DOM terms,
   this the string given by <code><var
   title="">element</var>.labels[0].textContent</code>). Otherwise, the value
   of the <code>value</code> attribute, if present, is the <a href="#label2"
   title=command-facet-Label>Label</a>. Otherwise, the <a href="#label2"
   title=command-facet-Label>Label</a> is the empty string.

  <p>The <a href="#hint" title=command-facet-Hint>Hint</a> of the command is
   the value of the <code title=attr-title><a href="#title">title</a></code>
   attribute of the <code>input</code> element. If the attribute is not
   present, the <a href="#hint" title=command-facet-Hint>Hint</a> is the
   empty string.

  <p>There is no <a href="#icon1" title=command-facet-Icon>Icon</a> for the
   command.

  <p>The <a href="#hidden1" title=command-facet-HiddenState>Hidden State</a>
   of the command is always false. (The command is never hidden.)

  <p>The <a href="#disabled6" title=command-facet-DisabledState>Disabled
   State</a> of the command mirrors the disabled state of the control.
   Typically this is given by the element's <code
   title=attr-input-disabled>disabled</code> attribute, but certain input
   types become disabled at other times too (for example, the
   <code>move-up</code> input type is disabled when it would have no effect).

  <p>The <a href="#checked2" title=command-facet-CheckedState>Checked
   State</a> of the command is true if the command is of <a href="#type16"
   title=command-facet-Type>Type</a> "radio" or "checkbox" and the element
   has a <code title=attr-input-checked>checked</code> attribute, and false
   otherwise.

  <p>The <a href="#action" title=command-facet-Action>Action</a> of the
   command is to <a href="#firing" title="fire a click event">fire a <code
   title="">click</code> event</a> at the element.</p>
  <!-- XXX this
  is probably wrong for radio and checkbox types, depending on how we
  define <input>. -->

  <h5 id=using2><span class=secno>3.18.5.4. </span><dfn id=using7
   title=option-command>Using the <code>option</code> element to define a
   command</dfn></h5>

  <p>An <code>option</code> element with an ancestor <code>select</code>
   element and either no <code title=attr-option-value>value</code> attribute
   or a <code title=attr-option-value>value</code> attribute that is not the
   empty string <a href="#command1" title=concept-command>defines a
   command</a>.

  <p>The <a href="#type16" title=command-facet-Type>Type</a> of the command
   is "radio" if the <code>option</code>'s nearest ancestor
   <code>select</code> element has no <code
   title=attr-select-multiple>multiple</code> attribute, and "checkbox" if it
   does.

  <p>The <a href="#id1" title=command-facet-ID>ID</a> of the command is the
   value of the <code title=attr-id><a href="#id">id</a></code> attribute of
   the element, if the attribute is present and not empty. Otherwise the
   command is an <a href="#anonymous">anonymous command</a>.

  <p>The <a href="#label2" title=command-facet-Label>Label</a> of the command
   is the value of the <code>option</code> element's <code
   title=attr-option-label>label</code> attribute, if there is one, or the
   value of the <code>option</code> element's <code><a
   href="#textcontent">textContent</a></code> DOM attribute if it doesn't.

  <p>The <a href="#hint" title=command-facet-Hint>Hint</a> of the command is
   the string given by the element's <code title=attr-title><a
   href="#title">title</a></code> attribute, if any, and the empty string if
   the attribute is absent.

  <p>There is no <a href="#icon1" title=command-facet-Icon>Icon</a> for the
   command.

  <p>The <a href="#hidden1" title=command-facet-HiddenState>Hidden State</a>
   of the command is always false. (The command is never hidden.)

  <p>The <a href="#disabled6" title=command-facet-DisabledState>Disabled
   State</a> of the command is true (disabled) if the element has a <code
   title=attr-option-disabled>disabled</code> attribute, and false otherwise.

  <p>The <a href="#checked2" title=command-facet-CheckedState>Checked
   State</a> of the command is true (checked) if the element's <code
   title=dom-option-selected>selected</code> DOM attribute is true, and false
   otherwise.

  <p>The <a href="#action" title=command-facet-Action>Action</a> of the
   command depends on its <a href="#type16"
   title=command-facet-Type>Type</a>. If the command is of <a href="#type16"
   title=command-facet-Type>Type</a> "radio" then this must set the <code
   title=dom-option-selected>selected</code> DOM attribute of the
   <code>option</code> element to true, otherwise it must toggle the state of
   the <code title=dom-option-selected>selected</code> DOM attribute (set it
   to true if it is false and vice versa). Then <a href="#firing0"
   title="fire a change event">a <code title="">change</code> event must be
   fired</a> on the <code>option</code> element's nearest ancestor
   <code>select</code> element (if there is one), as if the selection had
   been changed directly.

  <h5 id=using3><span class=secno>3.18.5.5. </span>Using the <dfn id=command3
   title=command-element><code>command</code></dfn> element to define a
   command</h5>

  <p>A <code><a href="#command0">command</a></code> element <a
   href="#command1" title=concept-command>defines a command</a>.

  <p>The <a href="#type16" title=command-facet-Type>Type</a> of the command
   is "radio" if the <code><a href="#command0">command</a></code>'s <code
   title=attr-command-type><a href="#type13">type</a></code> attribute is
   "<code>radio</code>", "checkbox" if the attribute's value is
   "<code>checkbox</code>", and "command" otherwise.

  <p>The <a href="#id1" title=command-facet-ID>ID</a> of the command is the
   value of the <code title=attr-id><a href="#id">id</a></code> attribute of
   the element, if the attribute is present and not empty. Otherwise the
   command is an <a href="#anonymous">anonymous command</a>.

  <p>The <a href="#label2" title=command-facet-Label>Label</a> of the command
   is the value of the element's <code title=attr-command-label><a
   href="#label">label</a></code> attribute, if there is one, or the empty
   string if it doesn't.

  <p>The <a href="#hint" title=command-facet-Hint>Hint</a> of the command is
   the string given by the element's <code title=attr-command-title><a
   href="#title6">title</a></code> attribute, if any, and the empty string if
   the attribute is absent.

  <p>The <a href="#icon1" title=command-facet-Icon>Icon</a> for the command
   is the absolute URI resulting from resolving the value of the element's
   <code title=attr-command-icon><a href="#icon">icon</a></code> attribute as
   a URI relative to the element's base URI. If the element has no <code
   title=attr-command-icon><a href="#icon">icon</a></code> attribute then the
   command has no <a href="#icon1" title=command-facet-Icon>Icon</a>.

  <p>The <a href="#hidden1" title=command-facet-HiddenState>Hidden State</a>
   of the command is true (hidden) if the element has a <code
   title=attr-command-hidden><a href="#hidden">hidden</a></code> attribute,
   and false otherwise.

  <p>The <a href="#disabled6" title=command-facet-DisabledState>Disabled
   State</a> of the command is true (disabled) if the element has either a
   <code title=attr-command-disabled><a href="#disabled4">disabled</a></code>
   attribute or a <code title=attr-command-hidden><a
   href="#hidden">hidden</a></code> attribute (or both), and false otherwise.

  <p>The <a href="#checked2" title=command-facet-CheckedState>Checked
   State</a> of the command is true (checked) if the element has a <code
   title=attr-command-checked><a href="#checked0">checked</a></code>
   attribute, and false otherwise.

  <p>The <a href="#action" title=command-facet-Action>Action</a> of the
   command is to invoke the behaviour described in the definition of the
   <code title=dom-command-click><a href="#click0">click()</a></code> method
   of the <code><a href="#htmlcommandelement">HTMLCommandElement</a></code>
   interface.</p>
  <!-- XXX update to
  point to dom-click when we remove dom-command-click -->

  <h3 id=miscellaneous><span class=secno>3.19. </span>Miscellaneous elements</h3>

  <h4 id=the-legend><span class=secno>3.19.1. </span>The <dfn
   id=legend><code>legend</code></dfn> element</h4>

  <dl class=element>
   <dt>Contexts in which this element may be used:

   <dd>As the first child of a <code>fieldset</code> element.

   <dd>As the first child of a <code><a href="#details">details</a></code>
    element.

   <dd>As a child of a <code><a href="#figure">figure</a></code> element, if
    there are no other <code><a href="#legend">legend</a></code> element
    children of that element.

   <dt>Content model:

   <dd>If used as a child of a <code>fieldset</code> or <code><a
    href="#details">details</a></code> element: <a href="#significant"
    title="significant inline content">significant</a> <a
    href="#strictly">strictly inline-level content</a>

   <dd>If used as a child of a <code><a href="#figure">figure</a></code>
    element: <a href="#inline-level0">inline-level content</a>.

   <dt>Element-specific attributes:

   <dd>None.

   <dt>DOM interface:

   <dd>No difference from <code><a
    href="#htmlelement">HTMLElement</a></code>.
  </dl>

  <p>The <code><a href="#legend">legend</a></code> element represents a title
   or explanatory caption for the rest of the contents of the <code><a
   href="#legend">legend</a></code> element's parent element.

  <h4 id=the-div><span class=secno>3.19.2. </span>The <dfn
   id=div><code>div</code></dfn> element</h4>

  <p><a href="#block-level0" title="block-level elements">Block-level
   element</a>.

  <dl class=element>
   <dt>Contexts in which this element may be used:

   <dd>Where <a href="#block-level0">block-level elements</a> are expected.

   <dt>Content model:

   <dd>Zero or more <code><a href="#style">style</a></code> elements,
    followed by either zero or more <a href="#block-level0">block-level
    elements</a>, or <a href="#inline-level0">inline-level content</a> (but
    not both).

   <dt>Element-specific attributes:

   <dd>None.

   <dt>DOM interface:

   <dd>No difference from <code><a
    href="#htmlelement">HTMLElement</a></code>.
  </dl>

  <p>The <code><a href="#div">div</a></code> element represents nothing at
   all. It can be used with the <code title=attr-class><a
   href="#class">class</a></code>, <code title=attr-lang><a
   href="#lang">lang</a></code>/<code title=attr-xml-lang><a
   href="#xmllang">xml:lang</a></code>, and <code title=attr-title><a
   href="#title">title</a></code> attributes to mark up semantics common to a
   group of consecutive elements.

  <h2 id=web-browsers><span class=secno>4. </span>Web browsers</h2>

  <p>This section describes features that apply most directly to Web
   browsers. Having said that, unless specified elsewhere, the requirements
   defined in this section <em>do</em> apply to all user agents, whether they
   are Web browsers or not.

  <h3 id=windows><span class=secno>4.1. </span>Browsing contexts</h3>

  <p>A <dfn id=browsing0>browsing context</dfn> is a collection of one or
   more <code>Document</code> objects, and one or more <a href="#view"
   title=view>views</a>.

  <p>At any one time, one of the <code>Document</code>s in a <a
   href="#browsing0">browsing context</a> is the <dfn id=active>active
   document</dfn>. The collection of <code>Document</code>s is the <a
   href="#browsing0">browsing context</a>'s <a href="#session">session
   history</a>.

  <p>A <dfn id=view>view</dfn> is a user agent interface tied to a particular
   media used for the presentation of <code>Document</code> objects in some
   media. A view may be interactive. Each view is represented by an
   <code>AbstractView</code> object. Each view belongs to a <a
   href="#browsing0">browsing context</a>. <a
   href="#refsDOM2VIEWS">[DOM2VIEWS]</a>

  <p class=note>The <code title="">document</code> attribute of an
   <code>AbstractView</code> object representing a <a href="#view">view</a>
   gives the <code>Document</code> object of the view's <a
   href="#browsing0">browsing context</a>'s <a href="#active">active
   document</a>. <a href="#refsDOM2VIEWS">[DOM2VIEWS]</a>

  <p class=note>Events that use the <code>UIEvent</code> interface are
   related to a specific <a href="#view">view</a> (the view in which the
   event happened); the <code>AbstractView</code> of that view is given in
   the event object's <code title="">view</code> attribute. <a
   href="#refsDOM3EVENTS">[DOM3EVENTS]</a>

  <p class=note>A typical Web browser has one obvious <a
   href="#view">view</a> per <a href="#browsing0">browsing context</a>: the
   browser's window (screen media). If a page is printed, however, a second
   view becomes evident, that of the print media. The two views always share
   the same underlying <code>Document</code>, but they have a different
   presentation of that document. A speech browser also establishes a
   browsing context, one with a view in the speech media.

  <p class=note>A <code>Document</code> does not necessarily have a <a
   href="#browsing0">browsing context</a> associated with it. In particular,
   data mining tools are likely to never instantiate browsing contexts.

  <p>The main <a href="#view">view</a> through which a user primarily
   interacts with a user agent is the <dfn id=default3>default view</dfn>.

  <p class=note>The <a href="#default3">default view</a> of a
   <code>Document</code> is given by the <code title="">defaultView</code>
   attribute on the <code>Document</code> object's <code>DocumentView</code>
   interface. <a href="#refsDOM3VIEWS">[DOM3VIEWS]</a>

  <p>When a <a href="#browsing0">browsing context</a> is first created, it
   must be created with a single <code>Document</code> in its session
   history, whose <span title="the document's address">address</span> is
   <code>about:blank</code>, which is marked as being an <a href="#html-"
   title="HTML documents">HTML documents</a>. The <code>Document</code> must
   have a single child <code><a href="#html">html</a></code> node, which
   itself has a single child <code><a href="#body0">body</a></code> node. If
   the <a href="#browsing0">browsing context</a> is created specifically to
   be immediately navigated, then that initial navigation will have <a
   href="#replacement">replacement enabled</a>.

  <h4 id=nested><span class=secno>4.1.1. </span>Nested browsing contexts</h4>

  <p>Certain elements (for example, <code><a href="#iframe">iframe</a></code>
   elements) can instantiate further <a href="#browsing0" title="browsing
   context">browsing contexts</a>. These are called <dfn id=nested0
   title="nested browsing context">nested browsing contexts</dfn>. If a
   browsing context <var title="">P</var> has an element in one of its
   <code>Document</code>s <var title="">D</var> that nests another browsing
   context <var title="">C</var> inside it, then <var title="">P</var> is
   said to be the <dfn id=parent>parent browsing context</dfn> of <var
   title="">C</var>, <var title="">C</var> is said to be a <dfn
   id=child>child browsing context</dfn> of <var title="">P</var>, and <var
   title="">C</var> is said to be <dfn id=nested1 title="browsing context
   nested through">nested through</dfn> <var title="">D</var>.

  <p>The browsing context with no <a href="#parent">parent browsing
   context</a> is the <dfn id=top-level>top-level browsing context</dfn> of
   all the browsing contexts <a href="#nested0" title="nested browsing
   context">nested</a> within it (either directly or indirectly through other
   nested browsing contexts).

  <p>A <code>Document</code> is said to be <dfn id=fully>fully active</dfn>
   when it is the <a href="#active">active document</a> of its <a
   href="#browsing0">browsing context</a>, and either its browsing context is
   a <a href="#top-level">top-level browsing context</a>, or the
   <code>Document</code> <a href="#nested1" title="browsing context nested
   through">through which</a> that browsing context is <a href="#nested0"
   title="nested browsing context">nested</a> is itself <a
   href="#fully">fully active</a>.

  <p>Because they are nested through an element, <a href="#child"
   title="child browsing context">child browsing contexts</a> are always tied
   to a specific <code>Document</code> in their <a href="#parent">parent
   browsing context</a>. User agents must not allow the user to interact with
   <a href="#child" title="child browsing context">child browsing
   contexts</a> of elements that are in <code>Document</code>s that are not
   themselves <a href="#fully">fully active</a>.

  <h4 id=auxiliary><span class=secno>4.1.2. </span>Auxiliary browsing
   contexts</h4>

  <p>It is possible to create new browsing contexts that are related to a
   <span>top level browsing context</span> without being nested through an
   element. Such browsing contexts are called <dfn id=auxiliary0
   title="auxiliary browsing context">auxiliary browsing contexts</dfn>.
   Auxiliary browsing contexts are always <a href="#top-level"
   title="top-level browsing context">top-level browsing contexts</a>.

  <p>An <a href="#auxiliary0">auxiliary browsing context</a> has an <dfn
   id=opener>opener browsing context</dfn>, which is the <a
   href="#browsing0">browsing context</a> from which the <a
   href="#auxiliary0">auxiliary browsing context</a> was created, and it has
   a <dfn id=furthest>furthest ancestor browsing context</dfn>, which is the
   <a href="#top-level">top-level browsing context</a> of the <a
   href="#opener">opener browsing context</a> when the <a
   href="#auxiliary0">auxiliary browsing context</a> was created.

  <p>The <dfn id=opener0 title=dom-opener><code>opener</code></dfn> DOM
   attribute on the <code><a href="#window">Window</a></code> object must
   return the <code><a href="#window">Window</a></code> object of the <a
   href="#browsing0">browsing context</a> from which the current browsing
   context was created (its <a href="#opener">opener browsing context</a>),
   if there is one and it is still available.

  <h4 id=secondary><span class=secno>4.1.3. </span>Secondary browsing
   contexts</h4>

  <p>User agents may support <dfn id=secondary0 title="secondary browsing
   context">secondary browsing contexts</dfn>, which are <a href="#browsing0"
   title="browsing context">browsing contexts</a> that form part of the user
   agent's interface, apart from the main content area.

  <h4 id=threads><span class=secno>4.1.4. </span>Threads</h4>

  <p>Each <a href="#browsing0">browsing context</a> is defined as having a
   list of zero or more <dfn id=directly>directly reachable browsing
   contexts</dfn>. These are:

  <ul>
   <li>All the <a href="#browsing0">browsing context</a>'s <a href="#child"
    title="child browsing context">child browsing contexts</a>.

   <li>The <a href="#browsing0">browsing context</a>'s <a
    href="#parent">parent browsing context</a>.

   <li>All the <a href="#browsing0" title="browsing context">browsing
    contexts</a> that have the <a href="#browsing0">browsing context</a> as
    their <a href="#opener">opener browsing context</a>.

   <li>The <a href="#browsing0">browsing context</a>'s <a
    href="#opener">opener browsing context</a>.
  </ul>

  <p>The transitive closure of all the <a href="#browsing0" title="browsing
   context">browsing contexts</a> that are <a href="#directly">directly
   reachable browsing contexts</a> consists of a <dfn id=unit-of>unit of
   related browsing contexts</dfn>.

  <p>All the executable code in a <a href="#unit-of">unit of related browsing
   contexts</a> must execute on a single conceptual thread. The dispatch of
   events fired by the user agent (e.g. in response to user actions or
   network activity) and the execution of any scripts associated with timers
   must be serialised so that for each <a href="#unit-of">unit of related
   browsing contexts</a> there is only one script being executed at a time.

  <h4 id=browsing><span class=secno>4.1.5. </span>Browsing context names</h4>

  <p>Browsing contexts can have a <dfn id=browsing1>browsing context
   name</dfn>. By default, a browsing context has no name (its name is not
   set).

  <p>A <dfn id=valid8>valid browsing context name</dfn> is any string that
   does not start with a U+005F LOW LINE character, or, a string that
   case-insensitively <!-- ASCII --> matches one of: <!--<code
  title="">_blank</code>,-->
   <code title="">_self</code>, <code title="">_parent</code>, or <code
   title="">_top</code>. (Names starting with an underscore are reserved for
   special keywords.)

  <p><dfn id=the-rules>The rules for chosing a browsing context given a
   browsing context name</dfn> are as follows. The rules assume that they are
   being applied in the context of a <a href="#browsing0">browsing
   context</a>.

  <ol>
   <li>
    <p>If the given browsing context name is the empty string or <code
     title="">_self</code>, then the chosen browsing context must be the
     current one.

   <li>
    <p>If the given browsing context name is <code title="">_parent</code>,
     then the chosen browsing context must be the <a
     href="#parent"><em>parent</em> browsing context</a> of the current one,
     unless there isn't one, in which case the chosen browsing context must
     be the current browsing context.

   <li>
    <p>If the given browsing context name is <code title="">_top</code>, then
     the chosen browsing context must be the most <a
     href="#top-level">top-level browsing context</a> of the current one.

   <li>
    <p>If the given browsing context name is not <code title="">_blank</code>
     and there exists a browsing context whose <a href="#browsing1"
     title="browsing context name">name</a> is the same as the given browsing
     context name, and one of the following is true:

    <ul>
     <li>Either the <a href="#origin0">origin</a> of that browsing context's
      <a href="#active">active document</a> is the same as the <a
      href="#origin0">origin</a> of the current browsing context's <a
      href="#active">active document</a>,

     <li>Or that browsing context is an <a href="#auxiliary0">auxiliary
      browsing context</a> and its <a href="#opener">opener browsing
      context</a> is either the current browsing context or a browsing
      context that the user agent considers is closely enough related to the
      current browsing context,

     <li>Or that browsing context is not a <a href="#top-level">top-level
      browsing context</a>, and the <a href="#origin0">origin</a> of the <a
      href="#active">active document</a> of the <a href="#parent">parent
      browsing context</a> of that browsing context is the same as the <a
      href="#origin0">origin</a> of the current browsing context's <a
      href="#active">active document</a>,
    </ul>

    <p>...and the user agent determines that the two browsing contexts are
     related enough that it is ok if they reach each other, then that
     browsing context must be the chosen one. If there are multiple matching
     browsing contexts, the user agent should select one in some arbitrary
     consistent manner, such as the most recently opened, most recently
     focused, or more closely related.</p>

   <li>
    <p>Otherwise, a new browsing context is being requested, and what happens
     depends on the user agent's configuration and/or abilities:</p>

    <dl>
     <dt>If the user agent has been configured such that in this instance it
      will create a new browsing context

     <dd>A new <a href="#auxiliary0">auxiliary browsing context</a> must be
      created, with the <a href="#opener">opener browsing context</a> being
      the current one. If the given browsing context name is not <code
      title="">_blank</code>, then the new auxiliary browsing context's name
      must be the given browsing context name (otherwise, it has no name).
      The chosen browsing context must be this new browsing context. If it is
      immediately <a href="#navigate" title=navigate>navigated</a>, then the
      navigation will be done with <a href="#replacement">replacement
      enabled</a>.

     <dt>If the user agent has been configured such that in this instance it
      will reuse the current browsing context

     <dd>The chosen browsing context is the current browsing context.

     <dt>If the user agent has been configured such that in this instance it
      will not find a browsing context

     <dd>There must not be a chosen browsing context.
    </dl>
  </ol>

  <h3 id=the-default0><span class=secno>4.2. </span>The default view</h3>

  <p>The <code>AbstractView</code> object of <a href="#default3"
   title="default view">default views</a> must also implement the <code><a
   href="#window">Window</a></code> object.

  <pre class=idl>interface <dfn id=window>Window</dfn> {
  // the current browsing context
  readonly attribute <a href="#window">Window</a> <a href="#window0" title=dom-window>window</a>;
  readonly attribute <a href="#window">Window</a> <a href="#self" title=dom-self>self</a>;
           attribute DOMString <a href="#name3" title=dom-name>name</a>;
  readonly attribute <a href="#location2">Location</a> <a href="#location0" title=dom-document-location>location</a>;
  readonly attribute <a href="#history1">History</a> <a href="#history0" title=dom-history>history</a>;
  readonly attribute <a href="#undomanager">UndoManager</a> <a href="#undomanager0" title=dom-undoManager>undoManager</a>;
  <a href="#selection1">Selection</a> <a href="#getselection" title=dom-getSelection>getSelection</a>();

  // the user agent
  readonly attribute <a href="#clientinformation">ClientInformation</a> <a href="#navigator" title=dom-navigator>navigator</a>; <!-- XXX IE6 also has window.clientInformation pointing to this same object -->
  readonly attribute <a href="#storage2">Storage</a> <a href="#sessionstorage" title=dom-sessionStorage>sessionStorage</a>;
  readonly attribute <a href="#storagelist">StorageList</a> <a href="#globalstorage" title=dom-globalStorage>globalStorage</a>;
  <a href="#resultset">ResultSet</a> <a href="#executesql" title=dom-executeSql>executeSql</a>(in DOMString sqlStatement, <var title="">arguments...</var>);

  // modal user prompts
  void <a href="#alert" title=dom-alert>alert</a>(in DOMString message);
  boolean <a href="#confirm" title=dom-confirm>confirm</a>(in DOMString message);
  DOMString <a href="#prompt" title=dom-prompt>prompt</a>(in DOMString message);
  DOMString <a href="#prompt" title=dom-prompt>prompt</a>(in DOMString message, in DOMString default);
  void <a href="#print" title=dom-print>print</a>();

  // other browsing contexts
  readonly attribute <a href="#window">Window</a> <a href="#frames" title=dom-frames>frames</a>;
  readonly attribute unsigned long <a href="#length5" title=dom-length>length</a>;
  readonly attribute <a href="#window">Window</a> <a href="#opener0" title=dom-opener>opener</a>;
  <a href="#window">Window</a> <a href="#open2" title=dom-open>open</a>();
  <a href="#window">Window</a> <a href="#open2" title=dom-open>open</a>(in DOMString url);
  <a href="#window">Window</a> <a href="#open2" title=dom-open>open</a>(in DOMString url, in DOMString target);
  <a href="#window">Window</a> <a href="#open2" title=dom-open>open</a>(in DOMString url, in DOMString target, in DOMString features);
  <a href="#window">Window</a> <a href="#open2" title=dom-open>open</a>(in DOMString url, in DOMString target, in DOMString features, in DOMString replace);

  // <a href="#event3">event handler DOM attributes</a>
           attribute <span>EventListener</span> <a href="#onabort" title=handler-onabort>onabort</a>;
           attribute <span>EventListener</span> <a href="#onbeforeunload" title=handler-onbeforeunload>onbeforeunload</a>;
           attribute <span>EventListener</span> <a href="#onblur" title=handler-onblur>onblur</a>;
           attribute <span>EventListener</span> <a href="#onchange" title=handler-onchange>onchange</a>;
           attribute <span>EventListener</span> <a href="#onclick" title=handler-onclick>onclick</a>;
           attribute <span>EventListener</span> <a href="#oncontextmenu" title=handler-oncontextmenu>oncontextmenu</a>;
           attribute <span>EventListener</span> <a href="#ondblclick" title=handler-ondblclick>ondblclick</a>;
           attribute <span>EventListener</span> <a href="#ondrag" title=handler-ondrag>ondrag</a>;
           attribute <span>EventListener</span> <a href="#ondragend" title=handler-ondragend>ondragend</a>;
           attribute <span>EventListener</span> <a href="#ondragenter" title=handler-ondragenter>ondragenter</a>;
           attribute <span>EventListener</span> <a href="#ondragleave" title=handler-ondragleave>ondragleave</a>;
           attribute <span>EventListener</span> <a href="#ondragover" title=handler-ondragover>ondragover</a>;
           attribute <span>EventListener</span> <a href="#ondragstart" title=handler-ondragstart>ondragstart</a>;
           attribute <span>EventListener</span> <a href="#ondrop" title=handler-ondrop>ondrop</a>;
           attribute <span>EventListener</span> <a href="#onerror" title=handler-onerror>onerror</a>;
           attribute <span>EventListener</span> <a href="#onfocus" title=handler-onfocus>onfocus</a>;
           attribute <span>EventListener</span> <a href="#onkeydown" title=handler-onkeydown>onkeydown</a>;
           attribute <span>EventListener</span> <a href="#onkeypress" title=handler-onkeypress>onkeypress</a>;
           attribute <span>EventListener</span> <a href="#onkeyup" title=handler-onkeyup>onkeyup</a>;
           attribute <span>EventListener</span> <a href="#onload" title=handler-onload>onload</a>;
           attribute <span>EventListener</span> <a href="#onmessage" title=handler-onmessage>onmessage</a>;
           attribute <span>EventListener</span> <a href="#onmousedown" title=handler-onmousedown>onmousedown</a>;
           attribute <span>EventListener</span> <a href="#onmousemove" title=handler-onmousemove>onmousemove</a>;
           attribute <span>EventListener</span> <a href="#onmouseout" title=handler-onmouseout>onmouseout</a>;
           attribute <span>EventListener</span> <a href="#onmouseover" title=handler-onmouseover>onmouseover</a>;
           attribute <span>EventListener</span> <a href="#onmouseup" title=handler-onmouseup>onmouseup</a>;
           attribute <span>EventListener</span> <a href="#onmousewheel" title=handler-onmousewheel>onmousewheel</a>;
           attribute <span>EventListener</span> <a href="#onresize" title=handler-onresize>onresize</a>;
           attribute <span>EventListener</span> <a href="#onscroll" title=handler-onscroll>onscroll</a>;
           attribute <span>EventListener</span> <a href="#onselect" title=handler-onselect>onselect</a>;
           attribute <span>EventListener</span> <a href="#onsubmit" title=handler-onsubmit>onsubmit</a>;
           attribute <span>EventListener</span> <a href="#onunload" title=handler-onunload>onunload</a>;
};</pre>
  <!-- XXX XMLHttpRequest
          http://msdn.microsoft.com/workshop/author/dhtml/reference/objects/obj_window.asp
          http://www.mozilla.org/docs/dom/domref/dom_window_ref.html
          http://lxr.mozilla.org/mozilla/source/dom/public/idl/base/nsIDOMWindow.idl
   -->

  <p>The <dfn id=window0 title=dom-window><code>window</code></dfn>, <dfn
   id=frames title=dom-frames><code>frames</code></dfn>, <dfn id=self
   title=dom-self><code>self</code></dfn> DOM attributes must all return the
   <code><a href="#window">Window</a></code> object itself.

  <p>The <code><a href="#window">Window</a></code> object also provides the
   scope for script execution. Each <code>Document</code> in a <a
   href="#browsing0">browsing context</a> has an associated <dfn
   id=list-of2>list of added properties</dfn> which, when a document is <a
   href="#active" title="active document">active</a>, are available on the
   <code>Document</code>'s <a href="#default3">default view</a> <code><a
   href="#window">Window</a></code> object. A <code>Document</code> object's
   <a href="#list-of2">list of added properties</a> must be empty when the
   <code>Document</code> object is created.

  <p>Objects implementing the <code><a href="#window">Window</a></code>
   interface must also implement the <code>EventTarget</code> interface.

  <p class=note><code><a href="#window">Window</a></code> objects also <a
   href="#get" title=dom-item>have an implicit [[Get]] method</a> which
   returns <span>nested browsing contexts</span>.

  <h4 id=security1><span class=secno>4.2.1. </span>Security</h4>

  <p>User agents must raise a <a href="#security8">security exception</a>
   whenever any of the members of a <code><a href="#window">Window</a></code>
   object are accessed by scripts whose <a href="#origin0">origin</a> is not
   the same as the <code><a href="#window">Window</a></code> object's <a
   href="#browsing0">browsing context</a>'s <a href="#active">active
   document</a>'s origin, with the following exceptions:

  <ul>
   <li>The <code title=dom-location><a href="#location1">location</a></code>
    object
  </ul>

  <p>User agents must not allow scripts to override the <code
   title=dom-location><a href="#location1">location</a></code> object's
   setter.

  <h4 id=constructors><span class=secno>4.2.2. </span>Constructors</h4>

  <p>All <code><a href="#window">Window</a></code> objects must provide the
   following constructors:

  <dl>
   <dt><dfn id=audio2 title=dom-audio><code>Audio()</code></dfn>

   <dt><dfn id=audio3 title=dom-audio-s><code>Audio(<var
    title="">src</var>)</code></dfn>

   <dd>
    <p>When invoked as constructors, these must return a new <code><a
     href="#htmlaudioelement">HTMLAudioElement</a></code> object (a new
     <code><a href="#audio1">audio</a></code> element). If the <var
     title=src>src</var> argument is present, the object created must have
     its <code title=dom-media-src><a href="#src6">src</a></code> content
     attribute set to the provided value.

   <dt><dfn id=image0 title=dom-image><code>Image()</code></dfn>

   <dt><dfn id=imagein title=dom-image-w><code>Image(in unsigned long <var
    title="">w</var>)</code></dfn>

   <dt><dfn id=imagein0 title=dom-image-wh><code>Image(in unsigned long <var
    title="">w</var>, in unsigned long <var title="">h</var>)</code></dfn>

   <dd>
    <p>When invoked as corstructors, these must return a new <code><a
     href="#htmlimageelement">HTMLImageElement</a></code> object (a new
     <code><a href="#img">img</a></code> element). If the <var
     title="">h</var> argument is present, the new object's <code
     title=attr-img-height><a href="#height">height</a></code> content
     attribute must be set to <var title="">h</var>. If the <var
     title="">w</var> argument is present, the new object's <code
     title=attr-img-width><a href="#width">width</a></code> content attribute
     must be set to <var title="">w</var>.

   <dt><dfn id=option title=dom-option><code>Option()</code></dfn>

   <dt><dfn id=optionin title=dom-option-n><code>Option(in DOMString <var
    title="">name</var>)</code></dfn>

   <dt><dfn id=optionin0 title=dom-option-nv><code>Option(in DOMString <var
    title="">name</var>, in DOMString <var title="">value</var>)</code></dfn>

   <dd>
    <p>When invoked as constructors, these must return a new
     <code>HTMLOptionElement</code> object (a new <code>option</code>
     element). <span class=big-issue>need to define argument
     processing</span>
  </dl>

  <p class=big-issue>And when constructors are invoked but without using the
   constructor syntax...?

  <h4 id=apis-for><span class=secno>4.2.3. </span>APIs for creating and
   navigating browsing contexts by name</h4>

  <p>The <dfn id=open2 title=dom-open><code>open()</code></dfn> method on
   <code><a href="#window">Window</a></code> objects provides a mechanism for
   <a href="#navigate" title=navigate>navigating</a> an existing <a
   href="#browsing0">browsing context</a> or opening and navigating an <a
   href="#auxiliary0">auxiliary browsing context</a>.

  <p>The method has four arguments, though they are all optional.

  <p>The first argument, <var title="">url</var>, gives a URI (or IRI) for a
   page to load in the browsing context. If no arguments are provided, then
   the <var title="">url</var> argument defaults to
   "<code>about:blank</code><!-- XXX xref -->". The argument must be resolved
   to an absolute URI by <span class=big-issue>...</span>

  <p>The second argument, <var title="">target</var>, specifies the <a
   href="#browsing1" title="browsing context name">name</a> of the browsing
   context that is to be navigated. It must be a <a href="#valid8">valid
   browsing context name</a>. If fewer than two arguments are provided, then
   the <var title="">name</var> argument defaults to the value
   "<code>_blank</code>".

  <p>The third argument, <var title="">features</var>, has no effect and is
   supported for historical reasons only.

  <p>The fourth argument, <var title="">replace</var>, specifies whether or
   not the new page will <a href="#replacement" title="replacement
   enabled">replace</a> the page currently loaded in the browsing context,
   when <var title="">target</var> identifies an existing browsing context
   (as opposed to leaving the current page in the browsing context's <a
   href="#session">session history</a>). When three or fewer arguments are
   provided, <var title="">replace</var> defaults to false.

  <p>When the method is invoked, the user agent must first select a <a
   href="#browsing0">browsing context</a> to navigate by applying <a
   href="#the-rules">the rules for chosing a browsing context given a
   browsing context name</a> using the <var title="">target</var> argument as
   the name and the <a href="#browsing0">browsing context</a> of the script
   as the context in which the algorithm is executed, unless the user has
   indicated a preference, in which case the browsing context to navigate may
   instead be the one indicated by the user.

  <p class=example>For example, suppose there is a user agent that supports
   control-clicking a link to open it in a new tab. If a user clicks in that
   user agent on an element whose <code title=handler-onclick><a
   href="#onclick">onclick</a></code> handler uses the <code
   title=dom-open><a href="#open2">window.open()</a></code> API to open a
   page in an iframe, but, while doing so, holds the control key down, the
   user agent could override the selection of the target browsing context to
   instead target a new tab.

  <p>Then, the user agent must <a href="#navigate">navigate</a> the selected
   <a href="#browsing0">browsing context</a> to the URI given in <var
   title="">url</var>. If the <var title="">replace</var> is true, then <a
   href="#replacement" title="replacement enabled">replacement must be
   enabled</a>; otherwise, it must not be enabled unless the <a
   href="#browsing0">browsing context</a> was just created as part of the <a
   href="#the-rules">the rules for chosing a browsing context given a
   browsing context name</a>.

  <p>The <dfn id=name3 title=dom-name><code>name</code></dfn> attribute of
   the <code><a href="#window">Window</a></code> object must, on getting,
   return the current name of the <a href="#browsing0">browsing context</a>,
   and, on setting, set the name of the <a href="#browsing0">browsing
   context</a> to the new value.

  <p class=note>The name <a href="#resetBCName">gets reset</a> when the
   browsing context is navigated to another domain.

  <h4 id=accessing><span class=secno>4.2.4. </span>Accessing other browsing
   contexts</h4>

  <p>In ECMAScript implementations, objects that implement the <code><a
   href="#window">Window</a></code> interface must have a <dfn id=get
   title=dom-item>[[Get]]</dfn> method that, when invoked with a property
   name that is a number <var title="">i</var>, returns the <var
   title="">i</var>th <a href="#child">child browsing context</a> of the <a
   href="#active" title="active document">active</a> <code>Document</code>,
   sorted in document order of the elements nesting those browsing contexts.

  <p>The <dfn id=length5 title=dom-length><code>length</code></dfn> DOM
   attribute on the <code><a href="#window">Window</a></code> interface must
   return the number of <a href="#child" title="child browsing context">child
   browsing contexts</a> of the <a href="#active" title="active
   document">active</a> <code>Document</code>.

  <h3 id=history><span class=secno>4.3. </span>Session history and navigation</h3>

  <h4 id=the-session><span class=secno>4.3.1. </span>The session history of
   browsing contexts</h4>

  <p>The sequence of <code>Document</code>s in a <a
   href="#browsing0">browsing context</a> is its <dfn id=session>session
   history</dfn>.

  <p><code><a href="#history1">History</a></code> objects provide a
   representation of the pages in the session history of <a href="#browsing0"
   title="browsing context">browsing contexts</a>. Each browsing context has
   a distinct session history.

  <p>Each <code>Document</code> object in a browsing context's session
   history is associated with a unique instance of the <code><a
   href="#history1">History</a></code> object, although they all must model
   the same underlying session history.

  <p>The <dfn id=history0 title=dom-history><code>history</code></dfn>
   attribute of the <code><a href="#window">Window</a></code> interface must
   return the object implementing the <code><a
   href="#history1">History</a></code> interface for that <code><a
   href="#window">Window</a></code> object's <a href="#active">active
   document</a>.

  <p><code><a href="#history1">History</a></code> objects represent their <a
   href="#browsing0">browsing context</a>'s session history as a flat list of
   URIs and <a href="#state" title="state object">state objects</a>. (This
   does not imply that the UI need be linear. See the <a
   href="#history-notes">notes below</a>.)

  <p>Typically, the history list will consist of only URIs. However, a page
   can <a href="#pushstate" title=dom-history-pushState>add</a> <dfn id=state
   title="state object">state objects</dfn> between its entry in the session
   history and the next ("forward") entry. These are then <a href="#popstate"
   title=event-popstate>returned to the script</a> when the user (or script)
   goes back in the history, thus enabling authors to use the "navigation"
   metaphor even in one-page applications.

  <p>Entries that consist of <a href="#state" title="state object">state
   objects</a> share the same <code>Document</code> as the entry for the URI
   itself. Contiguous entries that differ just by fragment identifier must
   also share the same <code>Document</code>.

  <p class=note>All entries that share the same <code>Document</code> (and
   that are therefore merely different states of one particular document) are
   contiguous by definition.

  <p>At any point, one of the entries in the session history is the <dfn
   id=current0>current entry</dfn>. This is the entry representing the <a
   href="#active">active document</a> of the <a href="#browsing0">browsing
   context</a>. The <a href="#current0">current entry</a> is usually an entry
   for the <a href="#href5" title=dom-location-href>location</a> of the
   <code>Document</code>. However, it can also be one of the entries for <a
   href="#state" title="state object">state objects</a> added to the history
   by that document.

  <p>User agents may <dfn id=discard>discard</dfn> the DOMs of entries other
   than the <a href="#current0">current entry</a> that are not referenced
   from any script, reloading the pages afresh when the user or script
   navigates back to such pages. This specification does not specify when
   user agents should discard pages' DOMs and when they should cache them.
   See the section on the <code title=event-load><a
   href="#load0">load</a></code> and <code title=event-unload>unload</code>
   events for more details.</p>
  <!-- XXX crossref! -->

  <p>Entries that have had their DOM discarded must, for the purposes of the
   algorithms given below, act as if they had not. When the user or script
   navigates back or forwards to a page which has no in-memory DOM objects,
   any other entries that shared the same <code>Document</code> object with
   it must share the new object as well.

  <p>When a user agent discards the DOM from an entry in the session history,
   it must also discard all the entries from the first state object entry for
   that <code>Document</code> object up to and including the last entry for
   that <code>Document</code> object (including any non-state-object entries
   in that range, such as entries where the user navigated using fragment
   identifiers). These entries are not recreated if the user or script
   navigates back to the page. If there are no state object entries for that
   <code>Document</code> object then no entries are removed.

  <h4 id=the-history><span class=secno>4.3.2. </span>The <code><a
   href="#history1">History</a></code> interface</h4>

  <pre class=idl>interface <dfn id=history1>History</dfn> {
  readonly attribute long <a href="#length6" title=dom-history-length>length</a>;
  void <a href="#godelta" title=dom-history-go>go</a>(in long delta);
  void <a href="#go" title=dom-history-go-0>go</a>();
  void <a href="#back" title=dom-history-back>back</a>();
  void <a href="#forward" title=dom-history-forward>forward</a>();
  void <a href="#pushstate" title=dom-history-pushState>pushState</a>(in DOMObject data);
  void <a href="#clearstate" title=dom-history-clearState>clearState</a>();
};</pre>

  <p>The <dfn id=length6 title=dom-history-length><code>length</code></dfn>
   attribute of the <code><a href="#history1">History</a></code> interface
   must return the number of entries in this <a href="#session">session
   history</a>.

  <p>The actual entries are not accessible from script.

  <p>The <dfn id=godelta title=dom-history-go><code>go(<var
   title="">delta</var>)</code></dfn> method causes the UA to move the number
   of steps specified by <var title="">delta</var> in the session history.

  <p>If the index of the <a href="#current0">current entry</a> plus <var
   title="">delta</var> is less than zero or greater than or equal to the <a
   href="#length6" title=dom-history-length>number of items in the session
   history</a>, then the user agent must do nothing.

  <p>If the <var title="">delta</var> is zero, then the user agent must act
   as if the <code title=dom-location-reload>location.reload()</code> method
   was called instead.

  <p>Otherwise, the user agent must cause the current <a
   href="#browsing0">browsing context</a> to <a href="#traverse">traverse the
   history</a> to the specified entry, as described below. The <dfn
   id=specified>specified entry</dfn> is the one whose index equals the index
   of the <a href="#current0">current entry</a> plus <var
   title="">delta</var>.

  <p>When a user agent is required to <dfn id=traverse>traverse the
   history</dfn> to a specified entry, the user agent must act as follows:

  <ol>
   <li>If there is no longer a <code>Document</code> object for the entry in
    question, the user agent must <a href="#navigate">navigate</a> the
    browsing context to the location for that entry to preform an <a
    href="#entry">entry update</a> of that entry, and abort these steps. The
    "<a href="#navigate">navigate</a>" algorithm reinvokes this "traverse"
    algorithm to complete the traversal, at which point there <em>is</em> a
    <code>Document</code> object and so this step gets skipped.

   <li>
    <p>If appropriate, update the <a href="#current0">current entry</a> in
     the <a href="#browsing0">browsing context</a>'s <code>Document</code>
     object's <code><a href="#history1">History</a></code> object to reflect
     any state that the user agent wishes to persist.</p>

    <p class=example>For example, some user agents might want to persist the
     scroll position, or the values of form controls.</p>

   <li>
    <p>If there are any entries with state objects between the <a
     href="#current0">current entry</a> and the <a
     href="#specified">specified entry</a> (not inclusive), then the user
     agent must iterate through every entry between the current entry and the
     specified entry, starting with the entry closest to the current entry,
     and ending with the one closest to the specified entry. For each entry,
     if the entry is a state object, the user agent must <a
     href="#activating0">activate the state object</a>.

   <li>
    <p>If the <a href="#specified">specified entry</a> has a different
     <code>Document</code> object than the <a href="#current0">current
     entry</a> then the user agent must follow the following substeps:</p>

    <ol>
     <li>The user agent must move any properties that have been added to the
      browsing context's default view's <code><a
      href="#window">Window</a></code> object to the <a href="#active">active
      document</a>'s <code>Document</code>'s <a href="#list-of2">list of
      added properties</a>.

     <li>If the browsing context is a <a href="#top-level">top-level browsing
      context</a> (and not an <a href="#auxiliary0">auxiliary browsing
      context</a>), and the <a href="#origin0">origin</a> of the
      <code>Document</code> of the <a href="#specified">specified entry</a>
      is not the same as the <a href="#origin0">origin</a> of the
      <code>Document</code> of the <a href="#current0">current entry</a>,
      then the following sub-sub-steps must be run:
      <ol>
       <li>The current <a href="#browsing1">browsing context name</a> must be
        stored with all the entries in the history that are associated with
        <code>Document</code> objects with the same <a
        href="#origin0">origin</a> as the <a href="#active">active
        document</a> <em>and</em> that are contiguous with the <a
        href="#current0">current entry</a>.

       <li id=resetBCName>The browsing context's <a
        href="#browsing1">browsing context name</a> must be unset.
      </ol>

     <li>The user agent must make the <a href="#specified">specified
      entry</a>'s <code>Document</code> object the <a href="#active">active
      document</a> of the <a href="#browsing0">browsing context</a>.

     <li>If the <a href="#specified">specified entry</a> has a <a
      href="#browsing1">browsing context name</a> stored with it, then the
      following sub-sub-steps must be run:
      <ol>
       <li>The browsing context's <a href="#browsing1">browsing context
        name</a> must be set to the name stored with the specified entry.

       <li>Any <a href="#browsing1">browsing context name</a> stored with the
        entries in the history that are associated with <code>Document</code>
        objects with the same <a href="#origin0">origin</a> as the new <a
        href="#active">active document</a>, and that are contiguous with the
        specified entry, must be cleared.
      </ol>

     <li>The user agent must move any properties that have been added to the
      <a href="#active">active document</a>'s <code>Document</code>'s <a
      href="#list-of2">list of added properties</a> to browsing context's
      default view's <code><a href="#window">Window</a></code> object.
    </ol>

   <li>
    <p>If the specified entry is a state object, the user agent must <a
     href="#activating0" title="activate the state object">activate that
     state object</a>.

   <li>
    <p>User agents may also update other aspects of the document view when
     the location changes in this way, for instance the scroll position,
     values of form fields, etc.

   <li>
    <p>The <a href="#current0">current entry</a> is now the <a
     href="#specified">specified entry</a>.
  </ol>

  <p class=big-issue>how does the changing of the global attributes affect
   .watch() when seen from other Windows?

  <p>When the user navigates through a <a href="#browsing0">browsing
   context</a>, e.g. using a browser's back and forward buttons, the user
   agent must translate this action into the equivalent invocations of the
   <code title=dom-history-go><a href="#godelta">history.go(<var
   title="">delta</var>)</a></code> method on the various affected <code
   title=dom-window><a href="#window0">window</a></code> objects.

  <p>Some of the other members of the <code><a
   href="#history1">History</a></code> interface are defined in terms of the
   <code title=dom-history-go><a href="#godelta">go()</a></code> method, as
   follows:

  <table>
   <tbody>
    <tr>
     <th>Member

     <th>Definition

    <tr>
     <td><dfn id=go title=dom-history-go-0><code>go()</code></dfn>

     <td>Must do the same as <code title=dom-history-go><a
      href="#godelta">go(0)</a></code>

    <tr>
     <td><dfn id=back title=dom-history-back><code>back()</code></dfn>

     <td>Must do the same as <code title=dom-history-go><a
      href="#godelta">go(-1)</a></code>

    <tr>
     <td><dfn id=forward
      title=dom-history-forward><code>forward()</code></dfn>

     <td>Must do the same as <code title=dom-history-go><a
      href="#godelta">go(1)</a></code>
  </table>

  <p>The <dfn id=pushstate title=dom-history-pushState><code>pushState(<var
   title="">data</var>)</code></dfn> method adds a state object to the
   history.

  <p>When this method is invoked, the user agent must first remove from the
   <a href="#session">session history</a> any entries for that
   <code>Document</code> from the entry after the <a href="#current0">current
   entry</a> up to the last entry in the session history that references the
   same <code>Document</code> object, if any. If the <a
   href="#current0">current entry</a> is the last entry in the session
   history, or if there are no entries after the <a href="#current0">current
   entry</a> that reference the same <code>Document</code> object, then no
   entries are removed.

  <p>Then, the user agent must add a state object entry to the session
   history, after the <a href="#current0">current entry</a>, with the
   specified <var title="">data</var> as the state object.

  <p>Finally, the user agent must update the <a href="#current0">current
   entry</a> to be the this newly added entry.

  <p class=big-issue>There has been a suggestion that pushState() should take
   a URI and a string; the URI to allow for the page to be bookmarked, and
   the string to allow the UA to give the page a meaningful title in the
   history state, if it shows history state.</p>
  <!-- XXX could have four variants of pushState to allow
  with/without URI and with/without title. Or maybe URI only makes
  sense if there is a title. -->

  <p>User agents may limit the number of state objects added to the session
   history per page. If a page hits the UA-defined limit, user agents must
   remove the entry immediately after the first entry for that
   <code>Document</code> object in the session history after having added the
   new entry. (Thus the state history acts as a FIFO buffer for eviction, but
   as a LIFO buffer for navigation.)

  <p>The <dfn id=clearstate
   title=dom-history-clearState><code>clearState()</code></dfn> method
   removes all the state objects for the <code>Document</code> object from
   the session history.

  <p>When this method is invoked, the user agent must remove from the session
   history all the entries from the first state object entry for that
   <code>Document</code> object up to the last entry that references that
   same <code>Document</code> object, if any.

  <p>Then, if the <a href="#current0">current entry</a> was removed in the
   previous step, the <a href="#current0">current entry</a> must be set to
   the last entry for that <code>Document</code> object in the session
   history.

  <h4 id=activating><span class=secno>4.3.3. </span><dfn id=activating0
   title="activate the state object">Activating state objects</dfn></h4>

  <p>When a state object in the session history is activated (which happens
   in the cases described above), the user agent must fire a <dfn id=popstate
   title=event-popstate><code>popstate</code></dfn> event in no namespace on
   the <a href="#the-body0">the body element</a> using the <code><a
   href="#popstateevent">PopStateEvent</a></code> interface, with the state
   object in the <code title=dom-PopStateEvent-state><a
   href="#state0">state</a></code> attribute. This event bubbles but is not
   cancelable and has no default action.</p>
  <!-- XXX onpopstate should be defined somewhere -->

  <pre
   class=idl>interface <dfn id=popstateevent>PopStateEvent</dfn> : Event {
  readonly attribute DOMObject <a href="#state0" title=dom-PopStateEvent-state>state</a>;
  void <a href="#initpopstateevent" title=dom-PopStateEvent-initPopStateEvent>initPopStateEvent</a>(in DOMString typeArg, in boolean canBubbleArg, in boolean cancelableArg, in DOMObject statetArg);
  void <a href="#initpopstateeventns" title=dom-PopStateEvent-initPopStateEventNS>initPopStateEventNS</a>(in DOMString namespaceURIArg, in DOMString typeArg, in boolean canBubbleArg, in boolean cancelableArg, in DOMObject stateArg);
};</pre>

  <p>The <dfn id=initpopstateevent
   title=dom-PopStateEvent-initPopStateEvent><code>initPopStateEvent()</code></dfn>
   and <dfn id=initpopstateeventns
   title=dom-PopStateEvent-initPopStateEventNS><code>initPopStateEventNS()</code></dfn>
   methods must initialise the event in a manner analogous to the
   similarly-named methods in the DOM3 Events interfaces. <a
   href="#refsDOM3EVENTS">[DOM3EVENTS]</a>

  <p>The <dfn id=state0
   title=dom-PopStateEvent-state><code>state</code></dfn> attribute
   represents the context information for the event.

  <p class=big-issue>Should we coalesce these events if they occur while the
   page is away? (e.g. during traversal -- see above)

  <h4 id=the-location><span class=secno>4.3.4. </span>The <code><a
   href="#location2">Location</a></code> interface</h4>

  <p>Each <code>Document</code> object in a browsing context's session
   history is associated with a unique instance of a <code><a
   href="#location2">Location</a></code> object.

  <p>The <dfn id=location0
   title=dom-document-location><code>location</code></dfn> attribute of the
   <code><a href="#htmldocument">HTMLDocument</a></code> interface must
   return the <code><a href="#location2">Location</a></code> object for that
   <code>Document</code> object.

  <p>The <dfn id=location1 title=dom-location><code>location</code></dfn>
   attribute of the <code><a href="#window">Window</a></code> interface must
   return the <code><a href="#location2">Location</a></code> object for that
   <code><a href="#window">Window</a></code> object's <a
   href="#active">active document</a>.

  <p><code><a href="#location2">Location</a></code> objects provide a
   representation of the URI of their document, and allow the <a
   href="#current0">current entry</a> of the <a href="#browsing0">browsing
   context</a>'s session history to be changed, by adding or replacing
   entries in the <code title=dom-history><a
   href="#history0">history</a></code> object.

  <pre class=idl>interface <dfn id=location2>Location</dfn> {
  readonly attribute DOMString <a href="#href5" title=dom-location-href>href</a>;
  void <a href="#assign" title=dom-location-assign>assign</a>(in DOMString url);
  void <a href="#replace" title=dom-location-replace>replace</a>(in DOMString url);
  void <span title=dom-location-reload>reload</span>();

  // <a href="#uri-decomposition">URI decomposition attributes</a> <!-- blame brendan for these "innovative" names -->
  readonly attribute DOMString <a href="#protocol" title=dom-location-protocol>protocol</a>;
  readonly attribute DOMString <a href="#host" title=dom-location-host>host</a>;
  readonly attribute DOMString <a href="#hostname" title=dom-location-hostname>hostname</a>;
  readonly attribute DOMString <a href="#port" title=dom-location-port>port</a>;
  readonly attribute DOMString <a href="#pathname" title=dom-location-pathname>pathname</a>;
  readonly attribute DOMString <a href="#search" title=dom-location-search>search</a>;
  readonly attribute DOMString <a href="#hash" title=dom-location-hash>hash</a>;
};</pre>

  <p>In the ECMAScript DOM binding, objects implementing this interface must
   stringify to the same value as the <code title=dom-location-href><a
   href="#href5">href</a></code> attribute.

  <p id=settingLocation>In the ECMAScript DOM binding, the <code
   title="">location</code> members of the <code><a
   href="#htmldocument">HTMLDocument</a></code> and <code><a
   href="#window">Window</a></code> interfaces behave as if they had a
   setter: user agents must treats attempts to set these <code
   title="">location</code> attribute as attempts at setting the <code
   title=dom-location-href><a href="#href5">href</a></code> attribute of the
   relevant <code><a href="#location2">Location</a></code> object instead.

  <p>The <dfn id=href5 title=dom-location-href><code>href</code></dfn>
   attribute returns the address of the page represented by the associated
   <code>Document</code> object, as an absolute IRI reference.

  <p>On setting, <!--XXX Mozilla does this, but IE doesn't. What
  should we do?: the behaviour depends on the context in which the
  script that set the attribute is running. If the script ran as the
  direct result of the execution of a <code>script</code> element in
  the document represented by the <code>Location</code> object's
  associated <code>Document</code> object, then the user agent must
  act as if the <code title="dom-location-replace">replace()</code>
  method had been called with the new value as its
  argument. Otherwise,-->
   the user agent must act as if the <code title=dom-location-assign><a
   href="#assign">assign()</a></code> method had been called with the new
   value as its argument.</p>
  <!-- XXX may wish to allow
  replace instead as a UI improvement -->

  <p>When the <dfn id=assign title=dom-location-assign><code>assign(<var
   title="">url</var>)</code></dfn> method is invoked, the UA must <a
   href="#navigate">navigate</a> the <a href="#browsing0">browsing
   context</a> to the specified <var title="">url</var>.

  <p>When the <dfn id=replace title=dom-location-replace><code>replace(<var
   title="">url</var>)</code></dfn> method is invoked, the UA must <a
   href="#navigate">navigate</a> to the specified <var title="">url</var>
   with <a href="#replacement">replacement enabled</a>.

  <p>Relative <var title="">url</var> arguments for <code
   title=dom-location-assign><a href="#assign">assign()</a></code> and <code
   title=dom-location-replace><a href="#replace">replace()</a></code> must be
   resolved relative to the base URI of the script that made the method call.</p>
  <!-- XXX what about if the base URI is data: or
  javascript: or about: or something else without a way to resolve
  base URIs? -->

  <p>The <code><a href="#location2">Location</a></code> interface also has
   the complement of <a href="#uri-decomposition">URI decomposition
   attributes</a>, <dfn id=protocol
   title=dom-location-protocol><code>protocol</code></dfn>, <dfn id=host
   title=dom-location-host><code>host</code></dfn>, <dfn id=port
   title=dom-location-port><code>port</code></dfn>, <dfn id=hostname
   title=dom-location-hostname><code>hostname</code></dfn>, <dfn id=pathname
   title=dom-location-pathname><code>pathname</code></dfn>, <dfn id=search
   title=dom-location-search><code>search</code></dfn>, and <dfn id=hash
   title=dom-location-hash><code>hash</code></dfn>. These must follow the
   rules given for URI decomposition attributes, with the <a href="#input"
   title=concept-uda-input>input</a> being the address of the page
   represented by the associated <code>Document</code> object, as an absolute
   IRI reference (same as the <code title=dom-location-href><a
   href="#href5">href</a></code> attribute), and the <a href="#common3"
   title=concept-uda-setter>common setter action</a> being the same as
   setting the <code title=dom-location-href><a href="#href5">href</a></code>
   attribute to the new output value.</p>
  <!--
  <dfn title="dom-location-reload"><code>reload()</code></dfn>
  reload during resize event:
  redisplay the current page (without reloading it). This
  theoretically would have no effect but in practice can be useful to
  work around rendering bugs.

reload on shared Document updates all of them

user reload must be equivalent to .reload()
-->

  <h5 id=security2><span class=secno>4.3.4.1. </span>Security</h5>

  <p>User agents must raise a <a href="#security8">security exception</a>
   whenever any of the members of a <code><a
   href="#location2">Location</a></code> object are accessed by scripts whose
   <a href="#origin0">origin</a> is not the same as the <code><a
   href="#location2">Location</a></code> object's associated
   <code>Document</code>'s origin, with the following exceptions:

  <ul>
   <li>The <code title=dom-location-href><a href="#href5">href</a></code>
    setter
  </ul>

  <p>User agents must not allow scripts to override the <code
   title=dom-location-href><a href="#href5">href</a></code> attribute's
   setter.

  <h4 id=history-notes><span class=secno>4.3.5. </span>Implementation notes
   for session history</h4>

  <p><em>This section is non-normative.</em>

  <p>The <code><a href="#history1">History</a></code> interface is not meant
   to place restrictions on how implementations represent the session history
   to the user.

  <p>For example, session history could be implemented in a tree-like manner,
   with each page having multiple "forward" pages. This specification doesn't
   define how the linear list of pages in the <code title=dom-history><a
   href="#history0">history</a></code> object are derived from the actual
   session history as seen from the user's perspective.

  <p>Similarly, a page containing two <code><a
   href="#iframe">iframe</a></code>s has a <code title=dom-history><a
   href="#history0">history</a></code> object distinct from the <code><a
   href="#iframe">iframe</a></code>s' <code title=dom-history><a
   href="#history0">history</a></code> objects, despite the fact that typical
   Web browsers present the user with just one "Back" button, with a session
   history that interleaves the navigation of the two inner frames and the
   outer page.

  <p><strong>Security:</strong> It is suggested that to avoid letting a page
   "hijack" the history navigation facilities of a UA by abusing <code
   title=dom-history-pushState><a href="#pushstate">pushState()</a></code>,
   the UA provide the user with a way to jump back to the previous page
   (rather than just going back to the previous state). For example, the back
   button could have a drop down showing just the pages in the session
   history, and not showing any of the states. Similarly, an aural browser
   could have two "back" commands, one that goes back to the previous state,
   and one that jumps straight back to the previous page.

  <p>In addition, a user agent could ignore calls to <code
   title=dom-history-pushState><a href="#pushstate">pushState()</a></code>
   that are invoked on a timer, or from event handlers that do not represent
   a clear user action, or that are invoked in rapid succession.

  <h3 id=links><span class=secno>4.4. </span>Links</h3>

  <h4 id=hyperlink><span class=secno>4.4.1. </span>Hyperlink elements</h4>

  <p>The <code><a href="#a">a</a></code>, <code><a
   href="#area">area</a></code>, and <code><a href="#link">link</a></code>
   elements can, in certain situations described in the definitions of those
   elements, represent <dfn id=hyperlinks title=hyperlink>hyperlinks</dfn>.

  <p>The <dfn id=href6 title=attr-hyperlink-href><code>href</code></dfn>
   attribute on a hyperlink element must have a value that is a URI (or IRI).
   This URI is the <em>destination resource</em> of the hyperlink.

  <div class=note>
   <p>The <code title=attr-hyperlink-href><a href="#href6">href</a></code>
    attribute on <code><a href="#a">a</a></code> and <code><a
    href="#area">area</a></code> elements is not required; when those
    elements do not have <code title=attr-hyperlink-href><a
    href="#href6">href</a></code> attributes they do not represent
    hyperlinks.</p>

   <p>The <code title=attr-link-href><a href="#href1">href</a></code>
    attribute on the <code><a href="#link">link</a></code> element
    <em>is</em> required, but whether a <code><a href="#link">link</a></code>
    element represents a hyperlink or not depends on the value of the <code
    title=attr-link-rel><a href="#rel">rel</a></code> attribute of that
    element.</p>
  </div>

  <p>The <dfn id=target3
   title=attr-hyperlink-target><code>target</code></dfn> attribute, if
   present, must be a <a href="#valid8">valid browsing context name</a>. User
   agents use this name when <a href="#following0">following hyperlinks</a>.

  <p>The <dfn id=ping title=attr-hyperlink-ping><code>ping</code></dfn>
   attribute, if present, gives the URIs of the resources that are interested
   in being notified if the user follows the hyperlink. The value must be a
   space separated list of one or more URIs (or IRIs). The value is used by
   the user agent when <a href="#following0">following hyperlinks</a>.

  <p>For <code><a href="#a">a</a></code> and <code><a
   href="#area">area</a></code> elements that represent hyperlinks, the
   relationship between the document containing the hyperlink and the
   destination resource indicated by the hyperlink is given by the value of
   the element's <dfn id=rel3 title=attr-hyperlink-rel><code>rel</code></dfn>
   attribute, which must be an <a href="#unordered">unordered set of
   space-separated tokens</a>. The <a href="#linkTypes">allowed values and
   their meanings</a> are defined below. The <code
   title=attr-hyperlink-rel><a href="#rel3">rel</a></code> attribute has no
   default value. If the attribute is omitted or if none of the values in the
   attribute are recognised by the UA, then the document has no particular
   relationship with the destination resource other than there being a
   hyperlink between the two.

  <p>The <dfn id=media12 title=attr-hyperlink-media><code>media</code></dfn>
   attribute describes for which media the target document was designed. It
   is purely advisory. The value must be a valid media query. <a
   href="#refsMQ">[MQ]</a> The default, if the <code
   title=attr-hyperlink-media><a href="#media12">media</a></code> attribute
   is omitted or has an invalid value, is <code>all</code>.

  <p>The <dfn id=hreflang3
   title=attr-hyperlink-hreflang><code>hreflang</code></dfn> attribute on
   hyperlink elements, if present, gives the language of the linked resource.
   It is purely advisory. The value must be a valid RFC 3066 language code.
   <a href="#refsRFC3066">[RFC3066]</a> User agents must not consider this
   attribute authoritative &mdash; upon fetching the resource, user agents
   must only use language information associated with the resource to
   determine its language, not metadata included in the link to the resource.

  <p>The <dfn id=type17 title=attr-hyperlink-type><code>type</code></dfn>
   attribute, if present, gives the MIME type of the linked resource. It is
   purely advisory. The value must be a valid MIME type, optionally with
   parameters. <a href="#refsRFC2046">[RFC2046]</a> User agents must not
   consider the <code title=attr-hyperlink-type><a
   href="#type17">type</a></code> attribute authoritative &mdash; upon
   fetching the resource, user agents must not use metadata included in the
   link to the resource to determine its type.

  <h4 id=following><span class=secno>4.4.2. </span><dfn
   id=following0>Following hyperlinks</dfn></h4>

  <p>When a user <em>follows a hyperlink</em>, the user agent must <a
   href="#navigate">navigate</a> a <a href="#browsing0">browsing context</a>
   to the URI of the hyperlink.

  <p>The URI of the hyperlink is URI given by resolving the the <code
   title=attr-hyperlink-href><a href="#href6">href</a></code> attribute of
   that hyperlink relative to the hyperlink's element. In the case of
   server-side image maps, the URI of the hyperlink must further have its
   <var><a href="#hyperlink2">hyperlink suffix</a></var> appended to it.

  <p>If the user indicated a specific browsing context when following the
   hyperlink, or if the user agent is configured to follow hyperlinks by
   navigating a particular browsing context, then that must be the browsing
   context that is navigated.

  <p>Otherwise, if the hyperlink element is an <code><a
   href="#a">a</a></code> or <code><a href="#area">area</a></code> element
   that has a <code title=attr-hyperlink-target><a
   href="#target3">target</a></code> attribute, then the browsing context
   that is navigated must be chosen by applying <a href="#the-rules">the
   rules for chosing a browsing context given a browsing context name</a>,
   using the value of the <code title=attr-hyperlink-target><a
   href="#target3">target</a></code> attribute as the browsing context name.
   If these rules result in the creation of a new <a
   href="#browsing0">browsing context</a>, it must be navigated with <a
   href="#replacement">replacement enabled</a>.

  <p>Otherwise, if the hyperlink element is a <a href="#sidebar0"
   title=rel-sidebar-hyperlink>sidebar hyperlink</a> and the user agent
   implements a feature that can be considered a secondary browsing context,
   such a secondary browsing context may be selected as the browsing context
   to be navigated.

  <p>Otherwise, if the hyperlink element is an <code><a
   href="#a">a</a></code> or <code><a href="#area">area</a></code> element
   with no <code title=attr-hyperlink-target><a
   href="#target3">target</a></code> attribute, but one of the child nodes of
   <a href="#the-head0">the <code>head</code> element</a> is a <code><a
   href="#base">base</a></code> element with a <code
   title=attr-base-target><a href="#target">target</a></code> attribute, then
   the browsing context that is navigated must be chosen by applying <a
   href="#the-rules">the rules for chosing a browsing context given a
   browsing context name</a>, using the value of the <code
   title=attr-base-target><a href="#target">target</a></code> attribute of
   the first such <code><a href="#base">base</a></code> element as the
   browsing context name. If these rules result in the creation of a new <a
   href="#browsing0">browsing context</a>, it must be navigated with <a
   href="#replacement">replacement enabled</a>.

  <p>Otherwise, the browsing context that must be navigated is the same
   browsing context as the one which the hyperlink element itself is in.

  <h5 id=hyperlink0><span class=secno>4.4.2.1. </span>Hyperlink auditing</h5>

  <p>If an <code><a href="#a">a</a></code> or <code><a
   href="#area">area</a></code> hyperlink element has a <code
   title=attr-hyperlink-ping><a href="#ping">ping</a></code> attribute and
   the user follows the hyperlink, the user agent must take the <code
   title=attr-hyperlink-ping><a href="#ping">ping</a></code> attribute's
   value, strip leading and trailing <a href="#space" title="space
   character">spaces</a>, split the value on sequences of spaces, treat each
   resulting part as a URI (resolving relative URIs according to element's
   base URI) and then should send a request to each of the resulting URIs.
   This may be done in parallel with the primary request, and is independent
   of the result of that request.

  <p>User agents should allow the user to adjust this behaviour, for example
   in conjunction with a setting that disables the sending of HTTP Referrer
   headers. Based on the user's preferences, UAs may either <a
   href="#ignored">ignore</a> the <code title=attr-hyperlink-ping><a
   href="#ping">ping</a></code> attribute altogether, or selectively ignore
   URIs in the list (e.g. ignoring any third-party URIs).

  <p>For URIs that are HTTP URIs, the requests must be performed using the
   POST method (with an empty entity body in the request). User agents must
   ignore any entity bodies returned in the responses, but must, unless
   otherwise specified by the user, honour the HTTP headers &mdash; in
   particular, HTTP cookie headers. <a href="#refsRFC2965">[RFC2965]</a>

  <p class=note>To save bandwidth, implementors might wish to consider
   omitting optional headers such as <code>Accept</code> from these requests.

  <p>When the <code title=attr-hyperlink-ping><a href="#ping">ping</a></code>
   attribute is present, user agents should clearly indicate to the user that
   following the hyperlink will also cause secondary requests to be sent in
   the background, possibly including listing the actual target URIs.

  <div class=note>
   <p>The <code title=attr-hyperlink-ping><a href="#ping">ping</a></code>
    attribute is redundant with pre-existing technologies like HTTP redirects
    and JavaScript in allowing Web pages to track which off-site links are
    most popular or allowing advertisers to track click-through rates.</p>

   <p>However, the <code title=attr-hyperlink-ping><a
    href="#ping">ping</a></code> attribute provides these advantages to the
    user over those alternatives:</p>

   <ul>
    <li>It allows the user to see the final target URI unobscured.

    <li>It allows the UA to inform the user about the out-of-band
     notifications.

    <li>It allows the paranoid user to disable the notifications without
     losing the underlying link functionality.

    <li>It allows the UA to optimise the use of available network bandwidth
     so that the target page loads faster.
   </ul>

   <p>Thus, while it is possible to track users without this feature, authors
    are encouraged to use the <code title=attr-hyperlink-ping><a
    href="#ping">ping</a></code> attribute so that the user agent can improve
    <!-- XXX optimise? --> the user experience.</p>
   <!--
   XXX need a better way to end that sentence. It's what I mean, but
   it sounds kooky. -->
   </div>

  <h4 id=linkTypes><span class=secno>4.4.3. </span>Link types</h4>

  <p>The following table summarises the link types that are defined by this
   specification. This table is non-normative; the actual definitions for the
   link types are given in the next few sections.

  <p>In this section, the term <em>referenced document</em> refers to the
   resource identified by the element representing the link, and the term
   <em>current document</em> refers to the resource within which the element
   representing the link finds itself.

  <p>To determine which link types apply to a <code><a
   href="#link">link</a></code>, <code><a href="#a">a</a></code>, or <code><a
   href="#area">area</a></code> element, the element's <code
   title="">rel</code> attribute must be <a href="#split" title="split a
   string on spaces">split on spaces</a>. The resulting tokens are the link
   types that apply to that element.

  <table>
   <thead>
    <tr>
     <th rowspan=2>Link type

     <th colspan=2>Effect on...

     <th rowspan=2>Brief description

    <tr>
     <th><code><a href="#link">link</a></code>

     <th><code><a href="#a">a</a></code> and <code><a
      href="#area">area</a></code>

   <tbody>
    <tr>
     <td><code title=rel-alternate><a href="#alternate">alternate</a></code></td>
     <!-- second most used <link rel> value -->

     <td><a href="#hyperlink1" title="hyperlink link">Hyperlink</a>

     <td><a href="#hyperlinks">Hyperlink</a>

     <td>Gives alternate representations of the current document.

    <tr>
     <td><code title=rel-archives><a href="#archives">archives</a></code>

     <td><a href="#hyperlink1" title="hyperlink link">Hyperlink</a>

     <td><a href="#hyperlinks">Hyperlink</a>

     <td>Provides a link to a collection of records, documents, or other
      materials of historical interest.

    <tr>
     <td><code title=rel-author><a href="#author">author</a></code>

     <td><a href="#hyperlink1" title="hyperlink link">Hyperlink</a>

     <td><a href="#hyperlinks">Hyperlink</a>

     <td>Gives a link to the current document's author.

    <tr>
     <td><code title=rel-bookmark><a href="#bookmark">bookmark</a></code></td>
     <!-- fourth most used <a rel> value -->

     <td><em>not allowed</em>

     <td><a href="#hyperlinks">Hyperlink</a>

     <td>Gives the permalink for the nearest ancestor section.

    <tr>
     <td><code title=rel-contact><a href="#contact">contact</a></code></td>
     <!-- 8th most used <a rel> value -->

     <td><a href="#hyperlink1" title="hyperlink link">Hyperlink</a>

     <td><a href="#hyperlinks">Hyperlink</a>

     <td>Gives a link to contact information for the current document.

    <tr>
     <td><code title=rel-external><a href="#external">external</a></code></td>
     <!-- fifth and sixth most used <a rel> value (sixth is "external nofollow") -->

     <td><em>not allowed</em>

     <td><a href="#hyperlinks">Hyperlink</a>

     <td>Indicates that the referenced document is not part of the same site
      as the current document.

    <tr>
     <td><code title=rel-feed><a href="#feed">feed</a></code>

     <td><a href="#hyperlink1" title="hyperlink link">Hyperlink</a>

     <td><a href="#hyperlinks">Hyperlink</a>

     <td>Gives the address of a syndication feed for the current document.

    <tr>
     <td><code title=rel-first><a href="#first">first</a></code>

     <td><a href="#hyperlink1" title="hyperlink link">Hyperlink</a>

     <td><a href="#hyperlinks">Hyperlink</a>

     <td>Indicates that the current document is a part of a series, and that
      the first document in the series is the referenced document.

    <tr>
     <td><code title=rel-help><a href="#help">help</a></code>

     <td><a href="#hyperlink1" title="hyperlink link">Hyperlink</a>

     <td><a href="#hyperlinks">Hyperlink</a>

     <td>Provides a link to context-sensitive help.

    <tr>
     <td><code title=rel-icon><a href="#icon3">icon</a></code></td>
     <!-- link rel="shortcut icon" and its ilk are the fourth, sixth, and ninth most used values -->

     <td><a href="#links1" title="external resource link">External
      Resource</a>

     <td><em>not allowed</em>

     <td>Imports an icon to represent the current document.

    <tr>
     <td><code title=rel-index><a href="#index">index</a></code></td>
     <!-- used more than "top" and "contents" on <link> (though on <a>, "contents" wins) -->

     <td><a href="#hyperlink1" title="hyperlink link">Hyperlink</a>

     <td><a href="#hyperlinks">Hyperlink</a>

     <td>Gives a link to the document that provides a table of contents or
      index listing the current document.

    <tr>
     <td><code title=rel-last><a href="#last">last</a></code>

     <td><a href="#hyperlink1" title="hyperlink link">Hyperlink</a>

     <td><a href="#hyperlinks">Hyperlink</a>

     <td>Indicates that the current document is a part of a series, and that
      the last document in the series is the referenced document.

    <tr>
     <td><code title=rel-license><a href="#license">license</a></code></td>
     <!-- seventh most used <a rel> value -->

     <td><a href="#hyperlink1" title="hyperlink link">Hyperlink</a>

     <td><a href="#hyperlinks">Hyperlink</a>

     <td>Indicates that the current document is covered by the copyright
      license described by the referenced document.

    <tr>
     <td><code title=rel-next><a href="#next">next</a></code>

     <td><a href="#hyperlink1" title="hyperlink link">Hyperlink</a>

     <td><a href="#hyperlinks">Hyperlink</a>

     <td>Indicates that the current document is a part of a series, and that
      the next document in the series is the referenced document.

    <tr>
     <td><code title=rel-nofollow><a href="#nofollow">nofollow</a></code></td>
     <!-- most used <a rel> value (and sixth most used is "external nofollow") -->

     <td><em>not allowed</em>

     <td><a href="#hyperlinks">Hyperlink</a>

     <td>Indicates that the current document's original author or publisher
      does not endorse the referenced document.

    <tr>
     <td><code title=rel-pingback><a href="#pingback">pingback</a></code>

     <td><a href="#links1" title="external resource link">External
      Resource</a>

     <td><em>not allowed</em>

     <td>Gives the address of the pingback server that handles pingbacks to
      the current document.

    <tr>
     <td><code title=rel-prefetch><a href="#prefetch">prefetch</a></code>

     <td><a href="#links1" title="external resource link">External
      Resource</a>

     <td><em>not allowed</em>

     <td>Specifies that the target resource should be pre-emptively cached.

    <tr>
     <td><code title=rel-prev><a href="#prev">prev</a></code></td>
     <!-- prev is used more than previous -->

     <td><a href="#hyperlink1" title="hyperlink link">Hyperlink</a>

     <td><a href="#hyperlinks">Hyperlink</a>

     <td>Indicates that the current document is a part of a series, and that
      the previous document in the series is the referenced document.

    <tr>
     <td><code title=rel-search><a href="#search0">search</a></code></td>
     <!-- used quite a bit -->

     <td><a href="#hyperlink1" title="hyperlink link">Hyperlink</a>

     <td><a href="#hyperlinks">Hyperlink</a>

     <td>Gives a link to a resource that can be used to search through the
      current document and its related pages.

    <tr>
     <td><code title=rel-stylesheet><a
      href="#stylesheet">stylesheet</a></code></td>
     <!-- most commonly used <link rel> value, variants came in 7th, 8th, 12th, 17th... -->

     <td><a href="#links1" title="external resource link">External
      Resource</a>

     <td><em>not allowed</em>

     <td>Imports a stylesheet.

    <tr>
     <td><code title=rel-sidebar><a href="#sidebar">sidebar</a></code></td>
     <!-- used quite a bit -->

     <td><a href="#hyperlink1" title="hyperlink link">Hyperlink</a>

     <td><a href="#hyperlinks">Hyperlink</a>

     <td>Specifies that the referenced document, if retrieved, is intended to
      be shown in the browser's sidebar (if it has one).

    <tr>
     <td><code title=rel-tag><a href="#tag">tag</a></code></td>
     <!-- second and third most used <a rel> value (third is technically "category tag"). -->

     <td><a href="#hyperlink1" title="hyperlink link">Hyperlink</a>

     <td><a href="#hyperlinks">Hyperlink</a>

     <td>Gives a tag (identified by the given address) that applies to the
      current document.

    <tr>
     <td><code title=rel-up><a href="#up">up</a></code>

     <td><a href="#hyperlink1" title="hyperlink link">Hyperlink</a>

     <td><a href="#hyperlinks">Hyperlink</a>

     <td>Provides a link to a document giving the context for the current
      document.
  </table>

  <p>Some of the types described below list synonyms for these values. These
   are to be handled as specified by user agents, but must not be used in
   documents.</p>
  <!--XXX

  issues for rel="", etc:
   rel="alternate stylesheet"
   rel="script"
   rel="related" // see also
   which relationship combinations are allowed
   what multiple values might mean (multiple <a rel="top"> in the same document)
   http://www.euronet.nl/~tekelenb/WWW/LINK/
   http://shift.freezope.org/konq_rellinks/development_html
   http://hixie.ch/specs/html/link/001
   http://hixie.ch/specs/html/link/002
   http://www.hixie.ch/specs/html/metadata
   what UAs are supposed to do with this
   do something about http://microformats.org/wiki/rel-enclosure

mpt says:
> "As with <a> elements, when <link> elements that use these relationships    
> are present, UAs should render them. As with <a> elements, when <link>
> elements that use these relationships do not exist, UAs should not
> render them. UAs should not make <link> rendering any easier to hide
> than <a> rendering."
  
for microformats (e.g. to refer to an hcard from an hcalendar):         
rel=xref
<a> and <area> only
The href attribute's value must start with a '#' character.
Indicates an in-page cross-reference. For the purposes of data mining tools, the subtree rooted
at the first element with the given ID must be treated as if it was cloned and replaced the <a> element.

    -->

  <h5 id=link-type><span class=secno>4.4.3.1. </span>Link type "<dfn
   id=alternate title=rel-alternate><code>alternate</code></dfn>"</h5>

  <p>The <code title=rel-alternate><a href="#alternate">alternate</a></code>
   keyword may be used with <code><a href="#link">link</a></code>, <code><a
   href="#a">a</a></code>, and <code><a href="#area">area</a></code>
   elements. For <code><a href="#link">link</a></code> elements, if the <code
   title=attr-link-rel><a href="#rel">rel</a></code> attribute does not also
   contain the keyword <code title=rel-stylesheet><a
   href="#stylesheet">stylesheet</a></code>, it creates a <a
   href="#hyperlink1" title="hyperlink link">hyperlink</a>; but if it
   <em>does</em> also contains the keyword <code title=rel-stylesheet><a
   href="#stylesheet">stylesheet</a></code>, the <code title=rel-alternate><a
   href="#alternate">alternate</a></code> keyword instead modifies the
   meaning of the <code title=rel-stylesheet><a
   href="#stylesheet">stylesheet</a></code> keyword in the way described for
   that keyword, and the rest of this subsection doesn't apply.

  <p>The <code title=rel-alternate><a href="#alternate">alternate</a></code>
   keyword indicates that the referenced document is an alternate
   representation of the current document.

  <p>The nature of the referenced document is given by the <code
   title=attr-hyperlink-media><a href="#media12">media</a></code>, <code
   title=attr-hyperlink-hreflang><a href="#hreflang3">hreflang</a></code>,
   and <code title=attr-hyperlink-type><a href="#type17">type</a></code>
   attributes.

  <p>If the <code title=rel-alternate><a
   href="#alternate">alternate</a></code> keyword is used with the <code
   title=attr-hyperlink-media><a href="#media12">media</a></code> attribute,
   it indicates that the referenced document is intended for use with the
   media specified.

  <p>If the <code title=rel-alternate><a
   href="#alternate">alternate</a></code> keyword is used with the <code
   title=attr-hyperlink-hreflang><a href="#hreflang3">hreflang</a></code>
   attribute, and that attribute's value differs from the <a
   href="#root-element">root element</a>'s <a href="#language">language</a>,
   it indicates that the referenced document is a translation.

  <p>If the <code title=rel-alternate><a
   href="#alternate">alternate</a></code> keyword is used with the <code
   title=attr-hyperlink-type><a href="#type17">type</a></code> attribute, it
   indicates that the referenced document is a reformulation of the current
   document in the specified format.

  <p>The <code title=attr-hyperlink-media><a
   href="#media12">media</a></code>, <code title=attr-hyperlink-hreflang><a
   href="#hreflang3">hreflang</a></code>, and <code
   title=attr-hyperlink-type><a href="#type17">type</a></code> attributes can
   be combined when specified with the <code title=rel-alternate><a
   href="#alternate">alternate</a></code> keyword.

  <div class=example>
   <p>For example, the following link is a French translation that uses the
    PDF format:</p>

   <pre>&lt;link rel=alternate type=application/pdf hreflang=fr href=manual-fr></pre>
  </div>

  <p>If the <code title=rel-alternate><a
   href="#alternate">alternate</a></code> keyword is used with the <code
   title=attr-hyperlink-type><a href="#type17">type</a></code> attribute set
   to the value <code title="">application/rss+xml</code> or the value <code
   title="">application/atom+xml</code>, then the user agent must treat the
   link as it would if it had the <code title=rel-feed><a
   href="#feed">feed</a></code> keyword specified as well.

  <p>The <code title=rel-alternate><a href="#alternate">alternate</a></code>
   link relationship is transitive &mdash; that is, if a document links to
   two other documents with the link type "<code title=rel-alternate><a
   href="#alternate">alternate</a></code>", then, in addition to implying
   that those documents are alternative representations of the first
   document, it is also implying that those two documents are alternative
   representations of each other.

  <h5 id=link-type0><span class=secno>4.4.3.2. </span>Link type "<dfn
   id=archives title=rel-archives><code>archives</code></dfn>"</h5>

  <p>The <code title=rel-archives><a href="#archives">archives</a></code>
   keyword may be used with <code><a href="#link">link</a></code>, <code><a
   href="#a">a</a></code>, and <code><a href="#area">area</a></code>
   elements. For <code><a href="#link">link</a></code> elements, it creates a
   <a href="#hyperlink1" title="hyperlink link">hyperlink</a>.

  <p>The <code title=rel-archives><a href="#archives">archives</a></code>
   keyword indicates that the referenced document describes a collection of
   records, documents, or other materials of historical interest.

  <p class=example>A blog's index page could link to an index of the blog's
   past posts with <code title="">rel="archives"</code>.

  <p><strong>Synonyms</strong>: For historical reasons, user agents must also
   treat the keyword "<code title="">archive</code>" like the <code
   title=rel-archives><a href="#archives">archives</a></code> keyword.

  <h5 id=link-type1><span class=secno>4.4.3.3. </span>Link type "<dfn
   id=author title=rel-author><code>author</code></dfn>"</h5>

  <p>The <code title=rel-author><a href="#author">author</a></code> keyword
   may be used with <code><a href="#link">link</a></code>, <code><a
   href="#a">a</a></code>, and <code><a href="#area">area</a></code>
   elements. For <code><a href="#link">link</a></code> elements, it creates a
   <a href="#hyperlink1" title="hyperlink link">hyperlink</a>.

  <p>For <code><a href="#a">a</a></code> and <code><a
   href="#area">area</a></code> elements, the <code title=rel-author><a
   href="#author">author</a></code> keyword indicates that the referenced
   document provides further information about the author of the section that
   the element defining the hyperlink <a href="#applyToSection">applies</a>
   to.

  <p>For <code><a href="#link">link</a></code> elements, the <code
   title=rel-author><a href="#author">author</a></code> keyword indicates
   that the referenced document provides further information about the author
   for the page as a whole.

  <p class=note>The "referenced document" can be, and often is, a <code
   title="">mailto:</code> URI giving the e-mail address of the author. <a
   href="#refsMAILTO">[MAILTO]</a>

  <p><strong>Synonyms</strong>: For historical reasons, user agents must also
   treat <code><a href="#link">link</a></code>, <code><a
   href="#a">a</a></code>, and <code><a href="#area">area</a></code> elements
   that have a <code title="">rev</code> attribute with the value
   "<code>made</code>" as having the <code title=rel-author><a
   href="#author">author</a></code> keyword specified as a link relationship.

  <h5 id=link-type2><span class=secno>4.4.3.4. </span>Link type "<dfn
   id=bookmark title=rel-bookmark><code>bookmark</code></dfn>"</h5>

  <p>The <code title=rel-bookmark><a href="#bookmark">bookmark</a></code>
   keyword may be used with <code><a href="#a">a</a></code> and <code><a
   href="#area">area</a></code> elements.

  <p>The <code title=rel-bookmark><a href="#bookmark">bookmark</a></code>
   keyword gives a permalink for the nearest ancestor <code><a
   href="#article">article</a></code> element of the linking element in
   question, or of <a href="#associatedSection">the section the linking
   element is most closely associated with</a>, if there are no ancestor
   <code><a href="#article">article</a></code> elements.

  <div class=example>
   <p>The following snippet has three permalinks. A user agent could
    determine which permalink applies to which part of the spec by looking at
    where the permalinks are given.</p>

   <pre> ...
 &lt;body>
  &lt;h1>Example of permalinks&lt;/h1>
  &lt;div id="a">
   &lt;h2>First example&lt;/h2>
   &lt;p>&lt;a href="a.html" rel="bookmark">This&lt;/a> permalink applies to
   only the content from the first H2 to the second H2. The DIV isn't
   exactly that section, but it roughly corresponds to it.&lt;/p>
  &lt;/div>
  &lt;h2>Second example&lt;/h2>
  &lt;article id="b">
   &lt;p>&lt;a href="b.html" rel="bookmark">This&lt;/a> permalink applies to
   the outer ARTICLE element (which could be, e.g., a blog post).&lt;/p>
   &lt;article id="c">
    &lt;p>&lt;a href="c.html" rel="bookmark">This&lt;/a> permalink applies to
    the inner ARTICLE element (which could be, e.g., a blog comment).&lt;/p>
   &lt;/article>
  &lt;/article>
 &lt;/body>
 ...</pre>
  </div>

  <h5 id=link-type3><span class=secno>4.4.3.5. </span>Link type "<dfn
   id=contact title=rel-contact><code>contact</code></dfn>"</h5>

  <p>The <code title=rel-contact><a href="#contact">contact</a></code>
   keyword may be used with <code><a href="#link">link</a></code>, <code><a
   href="#a">a</a></code>, and <code><a href="#area">area</a></code>
   elements. For <code><a href="#link">link</a></code> elements, it creates a
   <a href="#hyperlink1" title="hyperlink link">hyperlink</a>.

  <p>For <code><a href="#a">a</a></code> and <code><a
   href="#area">area</a></code> elements, the <code title=rel-contact><a
   href="#contact">contact</a></code> keyword indicates that the referenced
   document provides further contact information for the section that the
   element defining the hyperlink <a href="#applyToSection">applies</a> to.

  <p>User agents must treat any hyperlink in an <code><a
   href="#address">address</a></code> element as having the <code
   title=rel-contact><a href="#contact">contact</a></code> link type
   specified.

  <p>For <code><a href="#link">link</a></code> elements, the <code
   title=rel-contact><a href="#contact">contact</a></code> keyword indicates
   that the referenced document provides further contact information for the
   page as a whole.

  <h5 id=link-type4><span class=secno>4.4.3.6. </span>Link type "<dfn
   id=external title=rel-external><code>external</code></dfn>"</h5>

  <p>The <code title=rel-external><a href="#external">external</a></code>
   keyword may be used with <code><a href="#a">a</a></code> and <code><a
   href="#area">area</a></code> elements.

  <p>The <code title=rel-external><a href="#external">external</a></code>
   keyword indicates that the link is leading to a document that is not part
   of the site that the current document forms a part of.

  <h5 id=link-type5><span class=secno>4.4.3.7. </span>Link type "<dfn id=feed
   title=rel-feed><code>feed</code></dfn>"</h5>

  <p>The <code title=rel-feed><a href="#feed">feed</a></code> keyword may be
   used with <code><a href="#link">link</a></code>, <code><a
   href="#a">a</a></code>, and <code><a href="#area">area</a></code>
   elements. For <code><a href="#link">link</a></code> elements, it creates a
   <a href="#hyperlink1" title="hyperlink link">hyperlink</a>.

  <p>The <code title=rel-feed><a href="#feed">feed</a></code> keyword
   indicates that the referenced document is a syndication feed. If the <code
   title=rel-alternate><a href="#alternate">alternate</a></code> link type is
   also specified, then the feed is specifically the feed for the current
   document; otherwise, the feed is just a syndication feed, not necessarily
   associated with a particular Web page.

  <p>The first <code><a href="#link">link</a></code>, <code><a
   href="#a">a</a></code>, or <code><a href="#area">area</a></code> element
   in the document (in tree order) that creates a hyperlink with the link
   type <code title=rel-feed><a href="#feed">feed</a></code> must be treated
   as the default syndication feed for the purposes of feed autodiscovery.

  <p class=note>The <code title=rel-feed><a href="#feed">feed</a></code>
   keyword is implied by the <code title=rel-alternate><a
   href="#alternate">alternate</a></code> link type in certain cases (q.v.).

  <div class=example>
   <p>The following two <code><a href="#link">link</a></code> elements are
    equivalent: both give the syndication feed for the current page:</p>

   <pre>&lt;link rel="alternate" type="application/atom+xml" href="data.xml"></pre>

   <pre>&lt;link rel="feed alternate" href="data.xml"></pre>

   <p>The following extract offers various different syndication feeds:</p>

   <pre> &lt;p>You can access the planets database using Atom feeds:&lt;/p>
 &lt;ul>
  &lt;li>&lt;a href="recently-visited-planets.xml" rel="feed">Recently Visited Planets&lt;/a>&lt;/li>
  &lt;li>&lt;a href="known-bad-planets.xml" rel="feed">Known Bad Planets&lt;/a>&lt;/li>
  &lt;li>&lt;a href="unexplored-planets.xml" rel="feed">Unexplored Planets&lt;/a>&lt;/li>
 &lt;/ul></pre>
  </div>

  <h5 id=link-type6><span class=secno>4.4.3.8. </span>Link type "<dfn id=help
   title=rel-help><code>help</code></dfn>"</h5>

  <p>The <code title=rel-help><a href="#help">help</a></code> keyword may be
   used with <code><a href="#link">link</a></code>, <code><a
   href="#a">a</a></code>, and <code><a href="#area">area</a></code>
   elements. For <code><a href="#link">link</a></code> elements, it creates a
   <a href="#hyperlink1" title="hyperlink link">hyperlink</a>.

  <p>For <code><a href="#a">a</a></code> and <code><a
   href="#area">area</a></code> elements, the <code title=rel-help><a
   href="#help">help</a></code> keyword indicates that the referenced
   document provides further help information for the parent of the element
   defining the hyperlink, and its children.

  <div class=example>
   <p>In the following example, the form control has associated
    context-sensitive help. The user agent could use this information, for
    example, displaying the referenced document if the user presses the
    "Help" or "F1" key.</p>

   <pre> &lt;p>&lt;label> Topic: &lt;input name=topic> &lt;a href="help/topic.html" rel="help">(Help)&lt;/a>&lt;/label>&lt;/p></pre>
  </div>

  <p>For <code><a href="#link">link</a></code> elements, the <code
   title=rel-help><a href="#help">help</a></code> keyword indicates that the
   referenced document provides help for the page as a whole.

  <h5 id=link-type7><span class=secno>4.4.3.9. </span>Link type "<dfn
   id=icon3 title=rel-icon><code>icon</code></dfn>"</h5>

  <p>The <code title=rel-icon><a href="#icon3">icon</a></code> keyword may be
   used with <code><a href="#link">link</a></code> elements, for which it
   creates an <a href="#links1" title="external resource link">external
   resource link</a>.

  <p>The specified resource is an icon representing the page or site, and
   should be used by the user agent when representing the page in the user
   interface.

  <p>Icons could be auditory icons, visual icons, or other kinds of icons. If
   multiple icons are provided, the user agent must select the most
   appropriate icon according to the <code title=attr-link-media><a
   href="#media0">media</a></code> attribute.

  <h5 id=link-type8><span class=secno>4.4.3.10. </span>Link type "<dfn
   id=license title=rel-license><code>license</code></dfn>"</h5>

  <p>The <code title=rel-license><a href="#license">license</a></code>
   keyword may be used with <code><a href="#link">link</a></code>, <code><a
   href="#a">a</a></code>, and <code><a href="#area">area</a></code>
   elements. For <code><a href="#link">link</a></code> elements, it creates a
   <a href="#hyperlink1" title="hyperlink link">hyperlink</a>.

  <p>The <code title=rel-license><a href="#license">license</a></code>
   keyword indicates that the referenced document provides the copyright
   license terms under which the current document is provided.

  <p><strong>Synonyms</strong>: For historical reasons, user agents must also
   treat the keyword "<code title="">copyright</code>" like the <code
   title=rel-license><a href="#license">license</a></code> keyword.

  <h5 id=link-type9><span class=secno>4.4.3.11. </span>Link type "<dfn
   id=nofollow title=rel-nofollow><code>nofollow</code></dfn>"</h5>

  <p>The <code title=rel-nofollow><a href="#nofollow">nofollow</a></code>
   keyword may be used with <code><a href="#a">a</a></code> and <code><a
   href="#area">area</a></code> elements.

  <p>The <code title=rel-nofollow><a href="#nofollow">nofollow</a></code>
   keyword indicates that the link is not endorsed by the original author or
   publisher of the page.

  <h5 id=link-type10><span class=secno>4.4.3.12. </span>Link type "<dfn
   id=pingback title=rel-pingback><code>pingback</code></dfn>"</h5>

  <p>The <code title=rel-pingback><a href="#pingback">pingback</a></code>
   keyword may be used with <code><a href="#link">link</a></code> elements,
   for which it creates an <a href="#links1" title="external resource
   link">external resource link</a>.

  <p>For the semantics of the <code title=rel-pingback><a
   href="#pingback">pingback</a></code> keyword, see the Pingback 1.0
   specification. <a href="#refsPINGBACK">[PINGBACK]</a>

  <h5 id=link-type11><span class=secno>4.4.3.13. </span>Link type "<dfn
   id=prefetch title=rel-prefetch><code>prefetch</code></dfn>"</h5>

  <p>The <code title=rel-prefetch><a href="#prefetch">prefetch</a></code>
   keyword may be used with <code><a href="#link">link</a></code> elements,
   for which it creates an <a href="#links1" title="external resource
   link">external resource link</a>.

  <p>The <code title=rel-prefetch><a href="#prefetch">prefetch</a></code>
   keyword indicates that preemptively fetching and caching the specified
   resource is likely to be beneficial, as it is highly likely that the user
   will require this resource.

  <h5 id=link-type12><span class=secno>4.4.3.14. </span>Link type "<dfn
   id=search0 title=rel-search><code>search</code></dfn>"</h5>

  <p>The <code title=rel-search><a href="#search0">search</a></code> keyword
   may be used with <code><a href="#link">link</a></code>, <code><a
   href="#a">a</a></code>, and <code><a href="#area">area</a></code>
   elements. For <code><a href="#link">link</a></code> elements, it creates a
   <a href="#hyperlink1" title="hyperlink link">hyperlink</a>.

  <p>The <code title=rel-search><a href="#search0">search</a></code> keyword
   indicates that the referenced document provides an interface specifically
   for searching the document and its related resources.

  <p class=note>OpenSearch description documents can be used with <code><a
   href="#link">link</a></code> elements and the <code title=rel-search><a
   href="#search0">search</a></code> link type to enable user agents to
   autodiscover search interfaces.

  <h5 id=link-type13><span class=secno>4.4.3.15. </span>Link type "<dfn
   id=stylesheet title=rel-stylesheet><code>stylesheet</code></dfn>"</h5>

  <p>The <code title=rel-stylesheet><a
   href="#stylesheet">stylesheet</a></code> keyword may be used with <code><a
   href="#link">link</a></code> elements, for which it creates an <a
   href="#links1" title="external resource link">external resource link</a>
   that contributes to the <a href="#styling0">styling processing model</a>.

  <p>The specified resource is a resource that describes how to present the
   document. Exactly how the resource is to be processed depends on the
   actual type of the resource.

  <p>If the <code title=rel-alternate><a
   href="#alternate">alternate</a></code> keyword is also specified on the
   <code><a href="#link">link</a></code> element, then the link is an
   alternative stylesheet.

  <h5 id=link-type14><span class=secno>4.4.3.16. </span>Link type "<dfn
   id=sidebar title=rel-sidebar><code>sidebar</code></dfn>"</h5>

  <p>The <code title=rel-sidebar><a href="#sidebar">sidebar</a></code>
   keyword may be used with <code><a href="#link">link</a></code>, <code><a
   href="#a">a</a></code>, and <code><a href="#area">area</a></code>
   elements. For <code><a href="#link">link</a></code> elements, it creates a
   <a href="#hyperlink1" title="hyperlink link">hyperlink</a>.

  <p>The <code title=rel-sidebar><a href="#sidebar">sidebar</a></code>
   keyword indicates that the referenced document, if retrieved, is intended
   to be shown in a <a href="#secondary0">secondary browsing context</a> (if
   possible), instead of in the current <a href="#browsing0">browsing
   context</a>.

  <p>A <a href="#hyperlinks" title=hyperlink>hyperlink element</a> with with
   the <code title=rel-sidebar><a href="#sidebar">sidebar</a></code> keyword
   specified is a <dfn id=sidebar0 title=rel-sidebar-hyperlink>sidebar
   hyperlink</dfn>.

  <h5 id=link-type15><span class=secno>4.4.3.17. </span>Link type "<dfn
   id=tag title=rel-tag><code>tag</code></dfn>"</h5>

  <p>The <code title=rel-tag><a href="#tag">tag</a></code> keyword may be
   used with <code><a href="#link">link</a></code>, <code><a
   href="#a">a</a></code>, and <code><a href="#area">area</a></code>
   elements. For <code><a href="#link">link</a></code> elements, it creates a
   <a href="#hyperlink1" title="hyperlink link">hyperlink</a>.

  <p>The <code title=rel-tag><a href="#tag">tag</a></code> keyword indicates
   that the <em>tag</em> that the referenced document represents applies to
   the current document.

  <h5 id=hierarchical><span class=secno>4.4.3.18. </span>Hierarchical link
   types</h5>

  <p>Some documents form part of a hierarchical structure of documents.

  <p>A hierarchical structure of documents is one where each document can
   have various subdocuments. A subdocument is said to be a <em>child</em> of
   the document it is a subdocument of. The document of which it is a
   subdocument is said to be its <em>parent</em>. The children of a document
   have a relative order; the subdocument that precedes another is its
   <em>previous sibling</em>, and the one that follows it is its <em>next
   sibling</em>. A document with no parent forms the top of the hierarchy.

  <h6 id=link-type16><span class=secno>4.4.3.18.1. </span>Link type "<dfn
   id=first title=rel-first><code>first</code></dfn>"</h6>

  <p>The <code title=rel-first><a href="#first">first</a></code> keyword may
   be used with <code><a href="#link">link</a></code>, <code><a
   href="#a">a</a></code>, and <code><a href="#area">area</a></code>
   elements. For <code><a href="#link">link</a></code> elements, it creates a
   <a href="#hyperlink1" title="hyperlink link">hyperlink</a>.

  <p>The <code title=rel-first><a href="#first">first</a></code> keyword
   indicates that the document is part of a hierarchical structure, and that
   the link is leading to the document that is the first child of the current
   document's parent document.

  <p><strong>Synonyms</strong>: For historical reasons, user agents must also
   treat the keywords "<code title="">begin</code>" and "<code
   title="">start</code>" like the <code title=rel-first><a
   href="#first">first</a></code> keyword.

  <h6 id=link-type17><span class=secno>4.4.3.18.2. </span>Link type "<dfn
   id=index title=rel-index><code>index</code></dfn>"</h6>

  <p>The <code title=rel-index><a href="#index">index</a></code> keyword may
   be used with <code><a href="#link">link</a></code>, <code><a
   href="#a">a</a></code>, and <code><a href="#area">area</a></code>
   elements. For <code><a href="#link">link</a></code> elements, it creates a
   <a href="#hyperlink1" title="hyperlink link">hyperlink</a>.

  <p>The <code title=rel-index><a href="#index">index</a></code> keyword
   indicates that the document is part of a hierarchical structure, and that
   the link is leading to the document that is the top of the hierarchy.

  <p><strong>Synonyms</strong>: For historical reasons, user agents must also
   treat the keywords "<code title="">top</code>", "<code
   title="">contents</code>", and "<code title="">toc</code>" like the <code
   title=rel-index><a href="#index">index</a></code> keyword.

  <h6 id=link-type18><span class=secno>4.4.3.18.3. </span>Link type "<dfn
   id=last title=rel-last><code>last</code></dfn>"</h6>

  <p>The <code title=rel-last><a href="#last">last</a></code> keyword may be
   used with <code><a href="#link">link</a></code>, <code><a
   href="#a">a</a></code>, and <code><a href="#area">area</a></code>
   elements. For <code><a href="#link">link</a></code> elements, it creates a
   <a href="#hyperlink1" title="hyperlink link">hyperlink</a>.

  <p>The <code title=rel-last><a href="#last">last</a></code> keyword
   indicates that the document is part of a hierarchical structure, and that
   the link is leading to the document that is the last child of the current
   document's parent document.

  <p><strong>Synonyms</strong>: For historical reasons, user agents must also
   treat the keyword "<code title="">end</code>" like the <code
   title=rel-last><a href="#last">last</a></code> keyword.

  <h6 id=link-type19><span class=secno>4.4.3.18.4. </span>Link type "<dfn
   id=next title=rel-next><code>next</code></dfn>"</h6>

  <p>The <code title=rel-next><a href="#next">next</a></code> keyword may be
   used with <code><a href="#link">link</a></code>, <code><a
   href="#a">a</a></code>, and <code><a href="#area">area</a></code>
   elements. For <code><a href="#link">link</a></code> elements, it creates a
   <a href="#hyperlink1" title="hyperlink link">hyperlink</a>.

  <p>The <code title=rel-next><a href="#next">next</a></code> keyword
   indicates that the document is part of a hierarchical structure, and that
   the link is leading to the document that is the next sibling of the
   current document.

  <h6 id=link-type20><span class=secno>4.4.3.18.5. </span>Link type "<dfn
   id=prev title=rel-prev><code>prev</code></dfn>"</h6>

  <p>The <code title=rel-prev><a href="#prev">prev</a></code> keyword may be
   used with <code><a href="#link">link</a></code>, <code><a
   href="#a">a</a></code>, and <code><a href="#area">area</a></code>
   elements. For <code><a href="#link">link</a></code> elements, it creates a
   <a href="#hyperlink1" title="hyperlink link">hyperlink</a>.

  <p>The <code title=rel-prev><a href="#prev">prev</a></code> keyword
   indicates that the document is part of a hierarchical structure, and that
   the link is leading to the document that is the previous sibling of the
   current document.

  <p><strong>Synonyms</strong>: For historical reasons, user agents must also
   treat the keyword "<code title="">previous</code>" like the <code
   title=rel-prev><a href="#prev">prev</a></code> keyword.

  <h6 id=link-type21><span class=secno>4.4.3.18.6. </span>Link type "<dfn
   id=up title=rel-up><code>up</code></dfn>"</h6>

  <p>The <code title=rel-up><a href="#up">up</a></code> keyword may be used
   with <code><a href="#link">link</a></code>, <code><a
   href="#a">a</a></code>, and <code><a href="#area">area</a></code>
   elements. For <code><a href="#link">link</a></code> elements, it creates a
   <a href="#hyperlink1" title="hyperlink link">hyperlink</a>.

  <p>The <code title=rel-up><a href="#up">up</a></code> keyword indicates
   that the document is part of a hierarchical structure, and that the link
   is leading to the document that is the parent of the current document.</p>
  <!-- idea: rel="up" vs rel="up up" vs rel="up up up top"
    this would allow you to do breadcrumbs:
     <nav>
      <p>
       <a href="/" rel="top up up up">Main</a> &gt;
       <a href="/products/" rel="up up">Products</a> &gt;
       <a href="/products/dishwashers" rel="up">Dishwashers</a> &gt;
       Second hand
      </p>
     </nav>
   -->

  <h5 id=other0><span class=secno>4.4.3.19. </span>Other link types</h5>

  <p>Other than the types defined above, only types defined as extensions in
   the <a href="http://wiki.whatwg.org/wiki/RelExtensions">WHATWG Wiki
   RelExtensions page</a> may be used with the <code title="">rel</code>
   attribute on <code><a href="#link">link</a></code>, <code><a
   href="#a">a</a></code>, and <code><a href="#area">area</a></code>
   elements. <a href="#refsWHATWGWIKI">[WHATWGWIKI]</a>

  <p>Anyone is free to edit the WHATWG Wiki RelExtensions page at any time to
   add a type. Extension types must be specified with the following
   information:

  <dl>
   <dt>Keyword

   <dd>
    <p>The actual value being defined. The value should not be confusingly
     similar to any other defined value (e.g. differing only in case).

   <dt>Effect on... <code><a href="#link">link</a></code>

   <dd>
    <p>One of the following:</p>

    <dl>
     <dt>not allowed

     <dd>The keyword is not allowed to be specified on <code><a
      href="#link">link</a></code> elements.

     <dt>Hyperlink

     <dd>The keyword may be specified on a <code><a
      href="#link">link</a></code> element; it creates a <a
      href="#hyperlink1" title="hyperlink link">hyperlink link</a>.

     <dt>External Resource

     <dd>The keyword may be specified on a <code><a
      href="#link">link</a></code> element; it creates a <a href="#links1"
      title="external resource link">external resource link</a>.
    </dl>

   <dt>Effect on... <code><a href="#a">a</a></code> and <code><a
    href="#area">area</a></code>

   <dd>
    <p>One of the following:</p>

    <dl>
     <dt>not allowed

     <dd>The keyword is not allowed to be specified on <code><a
      href="#a">a</a></code> and <code><a href="#area">area</a></code>
      elements.

     <dt>Hyperlink

     <dd>The keyword may be specified on <code><a href="#a">a</a></code> and
      <code><a href="#area">area</a></code> elements; it creates a <a
      href="#hyperlinks" title=hyperlink>hyperlink</a>.
    </dl>

   <dt>Brief description

   <dd>
    <p>A short description of what the keyword's meaning is.

   <dt>Link to more details

   <dd>
    <p>A link to a more detailed description of the keyword's semantics and
     requirements. It could be another page on the Wiki, or a link to an
     external page.

   <dt>Synonyms

   <dd>
    <p>A list of other keyword values that have exactly the same processing
     requirements. Authors must not use the values defined to be synonyms,
     they are only intended to allow user agents to support legacy content.

   <dt>Status

   <dd>
    <p>One of the following:</p>

    <dl>
     <dt>Proposal

     <dd>The keyword has not received wide peer review and approval. It is
      included for completeness because pages use the keyword. Pages should
      not use the keyword.

     <dt>Accepted

     <dd>The keyword has received wide peer review and approval. It has a
      specification that unambiguously defines how to handle pages that use
      the keyword, including when they use them in incorrect ways. Pages may
      use the keyword.

     <dt>Rejected

     <dd>The keyword has received wide peer review and it has been found to
      have significant problems. Pages must not use the keyword. When a
      keyword has this status, the "Effect on... <code><a
      href="#link">link</a></code>" and "Effect on... <code><a
      href="#a">a</a></code> and <code><a href="#area">area</a></code>"
      information should be set to "not allowed".
    </dl>

    <p>If a keyword is added with the "proposal" status and found to be
     redundant with existing values, it should be removed and listed as a
     synonym for the existing value. If a keyword is added with the
     "proposal" status and found to be harmful, then it should be changed to
     "rejected" status, and its "Effect on..." information should be changed
     accordingly.</p>
  </dl>

  <p>Conformance checkers must use the information given on the WHATWG Wiki
   RelExtensions page to establish if a value not explicitly defined in this
   specification is allowed or not. When an author uses a new type not
   defined by either this specification or the Wiki page, conformance
   checkers should offer to add the value to the Wiki, with the details
   described above, with the "proposal" status.

  <p>This specification does not define how new values will get approved. It
   is expected that the Wiki will have a community that addresses this.

  <h3 id=interfaces><span class=secno>4.5. </span>Interfaces for URI
   manipulation</h3>

  <p>An interface that has a complement of <dfn id=uri-decomposition>URI
   decomposition attributes</dfn> will have seven attributes with the
   following definitions:

  <pre class=idl>
  readonly attribute DOMString <a href="#protocol0" title=dom-uda-protocol>protocol</a>;
  readonly attribute DOMString <a href="#host0" title=dom-uda-host>host</a>;
  readonly attribute DOMString <a href="#hostname0" title=dom-uda-hostname>hostname</a>;
  readonly attribute DOMString <a href="#port0" title=dom-uda-port>port</a>;
  readonly attribute DOMString <a href="#pathname0" title=dom-uda-pathname>pathname</a>;
  readonly attribute DOMString <a href="#search1" title=dom-uda-search>search</a>;
  readonly attribute DOMString <a href="#hash0" title=dom-uda-hash>hash</a>;
</pre>

  <p>The attributes defined to be URI decomposition attributes must act as
   described for the attributes with the same corresponding names in this
   section.

  <p>In addition, an interface with a complement of URI decomposition
   attributes will define an <dfn id=input
   title=concept-uda-input>input</dfn>, which is a URI that the attributes
   act on, and a <dfn id=common3 title=concept-uda-setter>common setter
   action</dfn>, which is a set of steps invoked when any of the attributes'
   setters are invoked.

  <p>The seven URI decomposition attributes have similar requirements.

  <p>On getting, if the <a href="#input" title=concept-uda-input>input</a>
   fulfills the condition given in the "getter condition" column
   corresponding to the attribute in the table below, the user agent must
   return the part of the <a href="#input" title=concept-uda-input>input</a>
   URI given in the "component" column, with any prefixes specified in the
   "prefix" column appropriately added to the start of the string and any
   suffixes specified in the "suffix" column appropriately added to the end
   of the string. Otherwise, the attribute must return the empty string.

  <p>On setting, the new value must first be mutated as described by the
   "setter preprocessor" column, then mutated by %-escaping any characters in
   the new value that are not valid in the relevant component as given by the
   "component" column. Then, if the resulting new value fulfills the
   condition given in the "setter condition" column, the user agent must make
   a new string <var title="">output</var> by replacing the component of the
   URI given by the "component" column in the <a href="#input"
   title=concept-uda-input>input</a> URI with the new value; otherwise, the
   user agent must let <var title="">output</var> be equal to the <a
   href="#input" title=concept-uda-input>input</a>. Finally, the user agent
   must invoke the <a href="#common3" title=concept-uda-setter>common setter
   action</a> with the value of <var title="">output</var>.

  <p>The rules for parsing and constructing URIs are described in RFC 2396 as
   modified by RFC 2732. <a href="#refsRFC2396">[RFC2396]</a> <a
   href="#refsRFC2732">[RFC2732]</a>

  <table>
   <thead>
    <tr>
     <th>Attribute

     <th>Component

     <th>Getter Condition

     <th>Prefix

     <th>Suffix

     <th>Setter Preprocessor

     <th>Setter Condition

   <tbody>
    <tr>
     <td><dfn id=protocol0 title=dom-uda-protocol><code>protocol</code></dfn>
      

     <td>&lt;scheme&gt;

     <td>&mdash;

     <td>&mdash;

     <td>U+003A COLON ("<code title="">:</code>")

     <td>Remove all trailing U+003A COLON ("<code title="">:</code>")
      characters

     <td>The new value is not the empty string

    <tr>
     <td><dfn id=host0 title=dom-uda-host><code>host</code></dfn>

     <td>&lt;hostport&gt;

     <td><a href="#input" title=concept-uda-input>input</a> is hierarchical
      and uses a server-based naming authority

     <td>&mdash;

     <td>&mdash;

     <td>&mdash;

     <td>&mdash;

    <tr>
     <td><dfn id=hostname0 title=dom-uda-hostname><code>hostname</code></dfn>
      

     <td>&lt;host&gt;

     <td><a href="#input" title=concept-uda-input>input</a> is hierarchical
      and uses a server-based naming authority

     <td>&mdash;

     <td>&mdash;

     <td>Remove all leading U+002F SOLIDUS ("<code title="">/</code>")
      characters

     <td>&mdash;

    <tr>
     <td><dfn id=port0 title=dom-uda-port><code>port</code></dfn>

     <td>&lt;port&gt;

     <td><a href="#input" title=concept-uda-input>input</a> is hierarchical
      and uses a server-based naming authority

     <td>&mdash;

     <td>&mdash;

     <td>Remove any characters in the new value that are not in the range
      U+0030 DIGIT ZERO .. U+0039 DIGIT NINE

     <td>The new value is not the empty string

    <tr>
     <td><dfn id=pathname0 title=dom-uda-pathname><code>pathname</code></dfn>
      

     <td>&lt;abs_path&gt;

     <td><a href="#input" title=concept-uda-input>input</a> is hierarchical

     <td>&mdash;

     <td>&mdash;

     <td>If it has no leading U+002F SOLIDUS ("<code title="">/</code>")
      character, prepend a U+002F SOLIDUS ("<code title="">/</code>")
      character to the new value

     <td>&mdash;

    <tr>
     <td><dfn id=search1 title=dom-uda-search><code>search</code></dfn>

     <td>&lt;query&gt;

     <td><a href="#input" title=concept-uda-input>input</a> is hierarchical

     <td>U+003F QUESTION MARK ("<code title="">?</code>")

     <td>&mdash;

     <td>Remove one leading U+003F QUESTION MARK ("<code title="">?</code>")
      character, if any

     <td>&mdash;

    <tr>
     <td><dfn id=hash0 title=dom-uda-hash><code>hash</code></dfn>

     <td>&lt;fragment&gt;

     <td>Fragment identifier is longer than zero characters

     <td>U+0023 NUMBER SIGN ("<code title="">#</code>")

     <td>&mdash;

     <td>Remove one leading U+0023 NUMBER SIGN ("<code title="">#</code>")
      character, if any

     <td>&mdash;
  </table>
  <!--
  http://www.hixie.ch/tests/adhoc/dom/level0/location/components/
  http://lxr.mozilla.org/seamonkey/source/dom/src/base/nsLocation.cpp
  http://wp.netscape.com/eng/mozilla/3.0/handbook/javascript/ref_h-l.htm#84722
-->

  <h3 id=navigating><span class=secno>4.6. </span>Navigating across documents</h3>

  <p>Certain actions cause the <a href="#browsing0">browsing context</a> to
   <dfn id=navigate>navigate</dfn>. For example, <a href="#following0"
   title="following hyperlinks">following a hyperlink</a>, <span
   title="">form submission</span>, and the <code
   title=dom-window-open>window.open()</code> and <code
   title=dom-location-assign><a href="#assign">location.assign()</a></code>
   methods can all cause a browsing context to navigate. A user agent may
   also provide various ways for the user to explicitly cause a browsing
   context to navigate.

  <p>When a browsing context is navigated, the user agent must follow the
   following steps:

  <ol>
   <li>
    <p>Cancel any preexisting attempt to navigate the browsing context.

   <li>
    <p>If the new resource is the same as the current resource, but a
     fragment identifier has been specified, then <a href="#scrolling0"
     title=navigate-fragid>scroll the document to the specified element</a>
     and abort these steps.

   <li>
    <p>If the new resource is to be handled by displaying some sort of inline
     content, e.g. an error message because the specified scheme is not one
     of the supported protocols, or an inline prompt to allow the user to
     select <a href="#registerprotocolhandler"
     title=dom-navigator-registerProtocolHandler>a registered handler</a> for
     the given scheme, then <a href="#display" title="display a user agent
     page inline">display the inline content</a> and abort these steps.

   <li>
    <p>If the new resource is to be handled using a mechanism that does not
     affect the browsing context, then abort these steps and proceed with
     that mechanism instead.

   <li>
    <p>Start fetching the specified resource, as appropriate (e.g. performing
     an HTTP GET or POST operation, or reading the file from disk, or
     executing script in the case of a <a href="#the-javascript"
     title="javascript protocol"><code title="">javascript:</code> URI</a>).
     If this results in a redirect, return to step 2 with the new resource.

   <li>
    <p>Wait for one or more bytes to be available or for the user agent to
     establish that the resource in question is empty. During this time, the
     user agent may allow the user to cancel this navigation attempt or start
     other navigation attempts.

   <li>
    <p>If the document's out-of-band metadata (e.g. HTTP headers), not
     counting any <a href="#content-type8" title=Content-Type>type
     information</a> (such as the Content-Type HTTP header), requires some
     sort of processing that will not affect the browsing context, then
     perform that processing and abort these steps.</p>

    <div class=note>
     <p>Such processing might be triggered by, amongst other things, the
      following:</p>

     <ul class=brief>
      <li>HTTP status codes (e.g. 204 No Content or 205 Reset Content)

      <li>HTTP Content-Disposition headers

      <li>Network errors
     </ul>
    </div>

   <li>
    <p>Let <var title="">type</var> be <a href="#sniffed" title="Content-Type
     sniffing">the sniffed type of the resource</a>.

   <li>
    <p>If the user agent has been configured to process resources of the
     given <var title="">type</var> using some mechanism other than rendering
     the content in a <a href="#browsing0">browsing context</a>, then skip
     this step. Otherwise, if the <var title="">type</var> is one of the
     following types, jump to the appropriate entry in the following list,
     and process the resource as described there:</p>

    <dl class=switch>
     <dt>"text/html"

     <dd>Follow the steps given in the <a href="#page-load"
      title=navigate-html>HTML document</a> section, and abort these steps.

     <dt>Any type ending in "+xml"

     <dt>"application/xml"

     <dt>"text/xml"

     <dd>Follow the steps given in the <a href="#page-load0"
      title=navigate-xml>XML document</a> section. If that section determines
      that the content is <em>not</em> to be displayed as a generic XML
      document, then proceed to the next step in this overall set of steps.
      Otherwise, abort these steps.

     <dt>"text/plain"

     <dd>Follow the steps given in the <a href="#page-load1"
      title=navigate-text>plain text file</a> section, and abort these steps.

     <dt>A supported image type

     <dd>Follow the steps given in the <a href="#page-load2"
      title=navigate-image>image</a> section, and abort these steps.

     <dt>A type that will use an external application to render the content
      in the <a href="#browsing0">browsing context</a>

     <dd>Follow the steps given in the <a href="#page-load3"
      title=navigate-plugin>plugin</a> section, and abort these steps.
    </dl>

   <li id=navigate-non-Document>
    <p>If, given <var title="">type</var>, the new resource is to be handled
     by displaying some sort of inline content, e.g. a native rendering of
     the content, an error message because the specified type is not
     supported, or an inline prompt to allow the user to select <a
     href="#registercontenthandler"
     title=dom-navigator-registerContentHandler>a registered handler</a> for
     the given type, then <a href="#display" title="display a user agent page
     inline">display the inline content</a> and abort these steps.

   <li>
    <p>Otherwise, the document's <var title="">type</var> is such that the
     resource will not affect the browsing context, e.g. because the resource
     is to be handed to an external application. Process the resource
     appropriately.</p>
  </ol>

  <p>Some of the sections below, to which the above algorithm defers in
   certain cases, require the user agent to <dfn id=update>update the session
   history with the new page</dfn>. When a user agent is required to do this,
   it must follows the set of steps given below that is appropriate for the
   situation at hand. From the point of view of any script, these steps must
   occur atomically.

  <ol>
   <li>
    <p class=big-issue>pause for scripts

   <li>
    <p class=big-issue>onbeforeunload

   <li>
    <p class=big-issue>onunload

   <li>
    <dl>
     <dt>If the navigation was initiated for <dfn id=entry>entry update</dfn>
      of an entry

     <dd>
      <ol>
       <li>
        <p>Replace the entry being updated with a new entry representing the
         new resource and its <code>Document</code> object and related state.
         The user agent may propagate state from the old entry to the new
         entry (e.g. scroll position).

       <li>
        <p><a href="#traverse">Traverse the history</a> to the new entry.
      </ol>

     <dt>Otherwise

     <dd>
      <ol>
       <li>
        <p>Remove all the entries after the <a href="#current0">current
         entry</a> in the <a href="#browsing0">browsing context</a>'s
         <code>Document</code> object's <code><a
         href="#history1">History</a></code> object.</p>

        <p class=note>This <a href="#history-notes">doesn't necessarily have
         to affect</a><!--XXX change to auto-xref?--> the user agent's user
         interface.</p>

       <li>
        <p>Append a new entry at the end of the <code><a
         href="#history1">History</a></code> object representing the new
         resource and its <code>Document</code> object and related state.

       <li>
        <p><a href="#traverse">Traverse the history</a> to the new entry.

       <li>
        <p>If the navigation was initiated with <dfn
         id=replacement>replacement enabled</dfn>, remove the entry
         immediately before the new <a href="#current0">current entry</a> in
         the session history.
      </ol>
    </dl>
  </ol>

  <h4 id=read-html><span class=secno>4.6.1. </span><dfn id=page-load
   title=navigate-html>Page load processing model for HTML files</dfn></h4>

  <p>When an HTML document is to be loaded in a <a href="#browsing0">browsing
   context</a>, the user agent must create a <code>Document</code> object,
   mark it as being an <a href="#html-" title="HTML documents">HTML
   document</a>, create an <a href="#html-0">HTML parser</a>, associate it
   with the document, and begin to use the bytes provided for the document as
   the <a href="#input0">input stream</a> for that parser.

  <p class=note>The <a href="#input0">input stream</a> converts bytes into
   characters for use in the <span>tokeniser</span>. This process relies, in
   part, on character encoding information found in the real <a
   href="#content-type8" title=Content-Type>Content-Type metadata</a> of the
   resource; the "sniffed type" is not used for this purpose.</p>
  <!-- next two paragraphs are nearly identical to the navigate-text
  section, keep them in sync -->

  <p>When no more bytes are available, an EOF character is implied, which
   eventually causes a <code title=event-load><a
   href="#load0">load</a></code> event to be fired.

  <p>After creating the <code>Document</code> object, but potentially before
   the page has finished parsing, the user agent must <a
   href="#update">update the session history with the new page</a>.

  <h4 id=read-xml><span class=secno>4.6.2. </span><dfn id=page-load0
   title=navigate-xml>Page load processing model for XML files</dfn></h4>

  <p>When faced with displaying an XML file inline, user agents must first
   create a <code>Document</code> object, following the requirements of the
   XML and Namespaces in XML recommendations, RFC 3023, DOM3 Core, and other
   relevant specifications. <a href="#refsXML">[XML]</a> <a
   href="#refsXMLNS">[XMLNS]</a> <a href="#refsRFC3023">[RFC3023]</a> <a
   href="#refsDOM3CORE">[DOM3CORE]</a>

  <p>The actual HTTP headers and other metadata, not the headers as mutated
   or implied by the algorithms given in this specification, are the ones
   that must be used when determining the character encoding according to the
   rules given in the above specifications.

  <p>User agents may examine the namespace of the root <code>Element</code>
   node of this <code>Document</code> object to perform namespace-based
   dispatch to alternative processing tools, e.g. determining that the
   content is actually a syndication feed and passing it to a feed handler.
   If such processing is to take place, abort the steps in this section, and
   jump to <a href="#navigate-non-Document">step 10</a> in the <a
   href="#navigate">navigate</a> steps above.

  <p>Otherwise, then, with the newly created <code>Document</code>, the user
   agents must <a href="#update">update the session history with the new
   page</a>. User agents may do this before the complete document has been
   parsed (thus achieving <i>incremental rendering</i>).

  <p>Error messages from the parse process (e.g. namespace well-formedness
   errors) may be reported inline by mutating the <code>Document</code>.

  <h4 id=read-text><span class=secno>4.6.3. </span><dfn id=page-load1
   title=navigate-text>Page load processing model for text files</dfn></h4>

  <p>When a plain text document is to be loaded in a <a
   href="#browsing0">browsing context</a>, the user agent should create a
   <code>Document</code> object, mark it as being an <a href="#html-"
   title="HTML documents">HTML document</a>, create an <a href="#html-0">HTML
   parser</a>, associate it with the document, act as if the tokeniser had
   emitted a start tag token with the tag name "pre", set the <a
   href="#tokenisation0">tokenisation</a> stage's <a href="#content2">content
   model flag</a> to <i>PLAINTEXT</i>, and begin to pass the stream of
   characters in the plain text document to that tokeniser.

  <p>The rules for how to convert the bytes of the plain text document into
   actual characters are defined in RFC 2046, RFC 2646, and subsequent
   versions thereof. <a href="#refsRFC2046">[RFC2046]</a> <a
   href="#refsRFC2046">[RFC2646]</a></p>
  <!-- next two paragraphs are nearly identical to the navigate-html
  section and similar to the "non-DOM-inline-content" section, and the
  next three are similar to the navigate-image and navigate-plugin
  sections; keep them all in sync -->

  <p>When no more character are available, an EOF character is implied, which
   eventually causes a <code title=event-load><a
   href="#load0">load</a></code> event to be fired.

  <p>After creating the <code>Document</code> object, but potentially before
   the page has finished parsing, the user agent must <a
   href="#update">update the session history with the new page</a>.

  <p>User agents may add content to the <code><a href="#head">head</a></code>
   element of the <code>Document</code>, e.g. linking to stylesheet or an XBL
   binding, providing script, giving the document a <code><a
   href="#title1">title</a></code>, etc.

  <h4 id=read-image><span class=secno>4.6.4. </span><dfn id=page-load2
   title=navigate-image>Page load processing model for images</dfn></h4>

  <p>When an image resource is to be loaded in a <a
   href="#browsing0">browsing context</a>, the user agent should create a
   <code>Document</code> object, mark it as being an <a href="#html-"
   title="HTML documents">HTML document</a>, append an <code><a
   href="#html">html</a></code> element to the <code>Document</code>, append
   a <code><a href="#head">head</a></code> element and a <code><a
   href="#body0">body</a></code> element to the <code><a
   href="#html">html</a></code> element, append an <code><a
   href="#img">img</a></code> to the <code><a href="#body0">body</a></code>
   element, and set the <code title=attr-img-src><a
   href="#src">src</a></code> attribute of the <code><a
   href="#img">img</a></code> element to the address of the image.</p>
  <!-- next three paragraphs are similar to the navigate-text section,
  keep them in sync -->

  <p>Then, the user agent must act as if it had <a href="#stops" title="stop
   parsing">stopped parsing</a>.

  <p>After creating the <code>Document</code> object, but potentially before
   the page has finished fully loading, the user agent must <a
   href="#update">update the session history with the new page</a>.

  <p>User agents may add content to the <code><a href="#head">head</a></code>
   element of the <code>Document</code>, or attributes to the <code><a
   href="#img">img</a></code> element, e.g. to link to stylesheet or an XBL
   binding, to provide a script, to give the document a <code><a
   href="#title1">title</a></code>, etc.

  <h4 id=read-plugin><span class=secno>4.6.5. </span><dfn id=page-load3
   title=navigate-plugin>Page load processing model for content that uses
   plugins</dfn></h4>

  <p>When a resource that requires an external resource to be rendered is to
   be loaded in a <a href="#browsing0">browsing context</a>, the user agent
   should create a <code>Document</code> object, mark it as being an <a
   href="#html-" title="HTML documents">HTML document</a>, append an <code><a
   href="#html">html</a></code> element to the <code>Document</code>, append
   a <code><a href="#head">head</a></code> element and a <code><a
   href="#body0">body</a></code> element to the <code><a
   href="#html">html</a></code> element, append an <code><a
   href="#embed">embed</a></code> to the <code><a
   href="#body0">body</a></code> element, and set the <code
   title=attr-img-src><a href="#src">src</a></code> attribute of the <code><a
   href="#img">img</a></code> element to the address of the image.</p>
  <!-- next three paragraphs are similar to the navigate-text section,
  keep them in sync -->

  <p>Then, the user agent must act as if it had <a href="#stops" title="stop
   parsing">stopped parsing</a>.

  <p>After creating the <code>Document</code> object, but potentially before
   the page has finished fully loading, the user agent must <a
   href="#update">update the session history with the new page</a>.

  <p>User agents may add content to the <code><a href="#head">head</a></code>
   element of the <code>Document</code>, or attributes to the <code><a
   href="#embed">embed</a></code> element, e.g. to link to stylesheet or an
   XBL binding, or to give the document a <code><a
   href="#title1">title</a></code>.

  <h4 id=non-DOM-inline-content><span class=secno>4.6.6. </span>Page load
   processing model for inline content that doesn't have a DOM</h4>

  <p>When the user agent is to <dfn id=display>display a user agent page
   inline</dfn> in a <a href="#browsing0">browsing context</a>, the user
   agent should create a <code>Document</code> object, mark it as being an <a
   href="#html-" title="HTML documents">HTML document</a>, and then either
   associate that <code>Document</code> with a custom rendering that is not
   rendered using the normal <code>Document</code> rendering rules, or mutate
   that <code>Document</code> until it represents the content the user agent
   wants to render.</p>
  <!-- next two paragraphs are similar to the navigate-text section,
  keep them in sync -->

  <p>Once the page has been set up, the user agent must act as if it had <a
   href="#stops" title="stop parsing">stopped parsing</a>.

  <p>After creating the <code>Document</code> object, but potentially before
   the page has been completely set up, the user agent must <a
   href="#update">update the session history with the new page</a>.

  <h4 id=scroll-to-fragid><span class=secno>4.6.7. </span><dfn id=scrolling0
   title=navigate-fragid>Scrolling to a fragment identifier</dfn></h4>

  <p>When a user agent is supposed to scroll to a particular element, it may
   change the scrolling position of the document as desired, or perform any
   other relevant action.

  <p class=big-issue>how to get a "particular element" from a frag id --
   id="", name="", XPointer, etc; missing IDs (e.g. the infamous "#top")

  <p>Then, the user agent must <a href="#update">update the session history
   with the new page</a>, where "the new page" has the same
   <code>Document</code> as before, but potentially has a different scroll
   position.

  <h3 id=content-type-sniffing><span class=secno>4.7. </span>Determining the
   type of a new resource in a browsing context</h3>

  <p class=warning>It is imperative that the rules in this section be
   followed exactly. When two user agents use different heuristics for
   content type detection, security problems can occur. For example, if a
   server believes a contributed file to be an image (and thus benign), but a
   Web browser believes the content to be HTML (and thus capable of executing
   script), the end user can be exposed to malicious content, making the user
   vulnerable to cookie theft attacks and other cross-site scripting attacks.

  <p>The <dfn id=sniffed title="Content-Type sniffing">sniffed type of a
   resource</dfn> must be found as follows:

  <ol>
   <li>
    <p>If the resource was fetched over an HTTP protocol, and there is no
     HTTP Content-Encoding header, but there is an HTTP Content-Type header
     and it has a value whose bytes exactly match one of the following three
     lines:</p>

    <table>
     <thead>
      <tr>
       <th>Bytes in Hexadecimal

       <th>Textual representation

     <tbody>
      <tr><!-- Old Apache default -->

       <td>74 65 78 74 2f 70 6c 61 69 6e

       <td><code title="">text/plain</code>

      <tr><!-- Modern Apache default -->

       <td>74 65 78 74 2f 70 6c 61 69 6e 3b 20 63 68 61 72 73 65 74 3d 49 53
        4f 2d 38 38 35 39 2d 31

       <td><code title="">text/plain;&nbsp;charset=ISO-8859-1</code>

      <tr><!-- Debian's arbitrarily different Modern Apache default -->

       <td>74 65 78 74 2f 70 6c 61 69 6e 3b 20 63 68 61 72 73 65 74 3d 69 73
        6f 2d 38 38 35 39 2d 31

       <td><code title="">text/plain;&nbsp;charset=iso-8859-1</code>
    </table>

    <p>...then jump to the <em title="content-type sniffing: text or
     binary"><a href="#content-type4">text or binary</a></em> section below.</p>

   <li>
    <p>Let <var title="">official type</var> be the type given by the <a
     href="#content-type8" title=Content-Type>Content-Type metadata</a> for
     the resource (in lowercase<!-- XXX ASCII case folding -->, ignoring any
     parameters). If there is no such type, jump to the <em
     title="content-type sniffing: unknown type"><a
     href="#content-type5">unknown type</a></em> step below.

   <li>
    <p>If <var title="">official type</var> ends in "+xml", or if it is
     either "text/xml" or "application/xml", then the the sniffed type of the
     resource is <var title="">official type</var>; return that and abort
     these steps.
   </li>
   <!-- we don't want
   image/svg+xml going through the next step -->

   <li>
    <p>If <var title="">official type</var> is an image type supported by the
     user agent (e.g. "image/png", "image/gif", "image/jpeg", etc), then jump
     to the <em title="content-type sniffing: image"><a
     href="#content-type6">images</a></em> section below.

   <li>
    <p>If <var title="">official type</var> is "text/html", then jump to the
     <em title="content-type sniffing: feed or html"><a
     href="#content-type7">feed or HTML</a></em> section below.

   <li>
    <p>Otherwise, the sniffed type of the resource is <var title="">official
     type</var>.
  </ol>

  <h4 id=content-type0><span class=secno>4.7.1. </span><dfn
   id=content-type4>Content-Type sniffing: text or binary</dfn></h4>

  <ol>
   <li>
    <p>The user agent may wait for 512 or more bytes of the resource to be
     available.

   <li>
    <p>Let <var title="">n</var> be the smaller of either 512 or the number
     of bytes already available.

   <li>
    <p>If <var title="">n</var> is 4 or more, and the first bytes of the file
     match one of the following byte sets:</p>

    <table>
     <thead>
      <tr>
       <th>Bytes in Hexadecimal

       <th>Description

     <tbody>
      <tr>
       <td>FE FF

       <td>UTF-16BE BOM <!-- followed by a character --> or UTF-32LE BOM

      <tr>
       <td>FF FE

       <td>UTF-16LE BOM <!-- followed by a character -->

      <tr>
       <td>00 00 FE FF

       <td>UTF-32BE BOM <!-- this one is redundant with the one above
      <tr>
       <td>FF FE 00 00
       <td>UTF-32LE BOM
-->
        

      <tr>
       <td>EF BB BF

       <td>UTF-8 BOM
        <!-- followed by a character, or the first byte of a multiple character sequence -->
        <!-- nobody uses this
      <tr>
       <td>DD 73 66 73
       <td>UTF-EBCDIC BOM
-->
        
    </table>

    <p>...then the sniffed type of the resource is "text/plain".

   <li>
    <p>Otherwise, if any of the first <var title="">n</var> bytes of the
     resource are in one of the following byte ranges:</p>
    <!-- This byte list is based on RFC 2046 Section 4.1.2. Characters
    in the range 0x00-0X1F, with the exception of 0x09 - 0x0D (ASCII
    for TAB, LF, VT, FF, and CR), and character 0x1B (reportedly used
    by some encodings as a shift escape), are invalid. Thus, if we see
    them, we assume it's not text. -->
    
    <ul class=brief>
     <li> 0x00 - 0x08

     <li> 0x0E - 0x1A

     <li> 0x1C - 0x1F
    </ul>

    <p>...then the sniffed type of the resource is
     "application/octet-stream".

   <li>
    <p>Otherwise, the sniffed type of the resource is "text/plain".
  </ol>

  <h4 id=content-type1><span class=secno>4.7.2. </span><dfn
   id=content-type5>Content-Type sniffing: unknown type</dfn></h4>

  <ol>
   <li>
    <p>The user agent may wait for 512 or more bytes of the resource to be
     available.

   <li>
    <p>Let <var title="">stream length</var> be the smaller of either 512 or
     the number of bytes already available.

   <li>
    <p>For each row in the table below:</p>

    <ol>
     <li>Let <var title="">pattern length</var> be the length of the pattern
      (number of bytes described by the cell in the second column of the
      row).

     <li>If <var title="">pattern length</var> is smaller than <var
      title="">stream length</var> then skip this row.

     <li>Apply the "and" operator to the first <var title="">pattern
      length</var> bytes of the resource and the given mask (the bytes in the
      cell of first column of that row), and let the result be the <var
      title="">data</var>.

     <li>If the bytes of the <var title="">data</var> matches the given
      pattern bytes exactly, then the sniffed type of the resource is the
      type given in the cell of the third column in that row; abort these
      steps.
    </ol>

   <li>
    <p>As a last-ditch effort, jump to the <a href="#content-type4"
     title="content-type sniffing: text or binary">text or binary</a>
     section.
  </ol>

  <table>
   <thead>
    <tr>
     <th colspan=2>Bytes in Hexadecimal

     <th rowspan=2>Sniffed type

     <th rowspan=2>Comment

    <tr>
     <th>Mask

     <th>Pattern

   <tbody>
    <tr>
     <td>FF FF DF DF DF DF DF DF DF FF DF DF DF DF

     <td>3C 21 44 4F 43 54 59 50 45 20 48 54 4D 4C <!-- "<!DOCTYPE HTML" -->

     <td>text/html

     <td>The string "<code title="">&lt;!DOCTYPE HTML</code>" in US-ASCII or
      compatible encodings, case-insensitively.

    <tr>
     <td>FF DF DF DF DF

     <td>3C 48 54 4D 4C <!-- "<HTML" -->

     <td>text/html

     <td>The string "<code title="">&lt;HTML</code>" in US-ASCII or
      compatible encodings, case-insensitively.

    <tr>
     <td>FF FF FF FF FF

     <td>25 50 44 46 2D
      <!-- "%PDF-" (from http://lxr.mozilla.org/seamonkey/source/netwerk/streamconv/converters/nsUnknownDecoder.cpp#321) -->
      

     <td>application/pdf

     <td>The string "<code title="">%PDF-</code>", the PDF signature.

    <tr>
     <td>FF FF FF FF FF FF FF FF FF FF FF

     <td>25 21 50 53 2D 41 64 6F 62 65 2D
      <!-- "%!PS-Adobe-" (from http://lxr.mozilla.org/seamonkey/source/netwerk/streamconv/converters/nsUnknownDecoder.cpp#321) -->
      

     <td>application/postscript

     <td>The string "<code title="">%!PS-Adobe-</code>", the PostScript
      signature. <!-- copied from the section below -->

   <tbody>
    <tr>
     <td>FF FF FF FF FF FF

     <td>47 49 46 38 37 61 <!-- GIF87a -->

     <td>image/gif

     <td>The string "<code title="">GIF87a</code>", a GIF signature.

    <tr>
     <td>FF FF FF FF FF FF

     <td>47 49 46 38 39 61 <!-- GIF89a -->

     <td>image/gif

     <td>The string "<code title="">GIF89a</code>", a GIF signature.

    <tr>
     <td>FF FF FF FF FF FF FF FF

     <td>89 50 4E 47 0D 0A 1A 0A
      <!-- [TAB]PNG[CR][LF][EOF][LF]; 137 80 78 71 13 10 26 10 -->

     <td>image/png

     <td>The PNG signature.

    <tr>
     <td>FF FF FF

     <td>FF D8 FF
      <!-- SOI marker followed by the first byte of another marker -->

     <td>image/jpeg

     <td>A JPEG SOI marker followed by the first byte of another marker.
  </table>

  <p>User agents may support further types if desired, by implicitly adding
   to the above table. However, user agents should not use any other patterns
   for types already mentioned in the table above, as this could then be used
   for privilege escalation (where, e.g., a server uses the above table to
   determine that content is not HTML and thus safe from XSS attacks, but
   then a user agent detects it as HTML anyway and allows script to execute).

  <h4 id=content-type2><span class=secno>4.7.3. </span><dfn
   id=content-type6>Content-Type sniffing: image</dfn></h4>

  <p>If the first bytes of the file match one of the byte sequences in the
   first columns of the following table, then the sniffed type of the
   resource is the type given in the corresponding cell in the second column
   on the same row:

  <table>
   <thead>
    <tr>
     <th>Bytes in Hexadecimal

     <th>Sniffed type

     <th>Comment <!-- update the table above if you change this! -->

   <tbody>
    <tr>
     <td>47 49 46 38 37 61 <!-- GIF87a -->

     <td>image/gif

     <td>The string "<code title="">GIF87a</code>", a GIF signature.

    <tr>
     <td>47 49 46 38 39 61 <!-- GIF89a -->

     <td>image/gif

     <td>The string "<code title="">GIF89a</code>", a GIF signature.

    <tr>
     <td>89 50 4E 47 0D 0A 1A 0A
      <!-- [TAB]PNG[CR][LF][EOF][LF]; 137 80 78 71 13 10 26 10 -->

     <td>image/png

     <td>The PNG signature.

    <tr>
     <td>FF D8 FF
      <!-- SOI marker followed by the first byte of another marker -->

     <td>image/jpeg

     <td>A JPEG SOI marker followed by the first byte of another marker.
  </table>

  <p>User agents must ignore any rows for image types that they do not
   support.

  <p>Otherwise, the <i>sniffed type</i> of the resource is the same as its
   <var title="">official type</var>.

  <h4 id=content-type3><span class=secno>4.7.4. </span><dfn
   id=content-type7>Content-Type sniffing: feed or HTML</dfn></h4>
  <!-- mostly based on:
   http://blogs.msdn.com/rssteam/articles/PublishersGuide.aspx
   http://lxr.mozilla.org/seamonkey/source/browser/components/feeds/src/nsFeedSniffer.cpp#192
   http://lxr.mozilla.org/seamonkey/source/browser/components/feeds/src/nsFeedSniffer.cpp#127
  -->

  <ol>
   <li>
    <p>The user agent may wait for 512 or more bytes of the resource to be
     available.

   <li>
    <p>Let <var title="">s</var> be the stream of bytes, and let <span><var
     title="">s</var>[<var title="">i</var>]</span> represent the byte in
     <var title="">s</var> with position <var title="">i</var>, treating <var
     title="">s</var> as zero-indexed (so the first byte is at <span><var
     title="">i</var>=0</span>).

   <li>
    <p>If at any point this algorithm requires the user agent to determine
     the value of a byte in <var title="">s</var> which is not yet available,
     or which is past the first 512 bytes of the resource, or which is beyond
     the end of the resource, the user agent must stop this algorithm, and
     assume that the sniffed type of the resource is "text/html".</p>

    <p class=note>User agents are allowed, by the first step of this
     algorithm, to wait until the first 512 bytes of the resource are
     available.

   <li>
    <p>Initialise <var title="">pos</var> to 0.

   <li>
    <p>Examine <span><var title="">s</var>[<var title="">pos</var>]</span>.</p>

    <dl
     class=switch><!-- skip whitespace (S token as defined in XML 1.0 section 2.3; production [3] -->

     <dt>If it is 0x09 (ASCII tab), 0x20 (ASCII space), 0x0A (ASCII LF), or
      0x0D (ASCII CR)

     <dd>Increase <var title="">pos</var> by 1 and repeat this step.

     <dt>If it is 0x3C (ASCII "<code title="">&lt;</code>")

     <dd>Increase <var title="">pos</var> by 1 and go to the next step.

     <dt>If it is anything else

     <dd>The sniffed type of the resource is "text/html". Abort these steps.
    </dl>

   <li>
    <p>If the bytes with positions <var title="">pos</var> to <span><var
     title="">pos</var>+2</span> in <var title="">s</var> are exactly equal
     to 0x21, 0x2D, 0x2D respectively (ASCII for "<code
     title="">!--</code>"), then:</p>

    <ol>
     <li>Increase <var title="">pos</var> by 3.</li>
     <!-- skips past the " ! - - " -->

     <li>If the bytes with positions <span><var title="">pos</var></span> to
      <span><var title="">pos</var>+2</span> in <var title="">s</var> are
      exactly equal to 0x2D, 0x2D, 0x3E respectively (ASCII for "<code
      title="">--&gt;</code>"), then increase <var title="">pos</var> by 3
      and jump back to the previous step (step 5) in the overall algorithm in
      this section.

     <li>Otherwise, increase <var title="">pos</var> by 1.

     <li>Otherwise, return to step 2 in these substeps.
    </ol>

   <li>
    <p>If <span><var title="">s</var>[<var title="">pos</var>]</span> is 0x21
     (ASCII "<code title="">!</code>"):</p>
    <!-- this skips past a DOCTYPE if there is one. It is brain-dead
    because we don't have to be clever to parse the Atom and RSS x.y
    DOCTYPEs, as they don't do anything clever like have internal
    subsets of quoted ">" characters. If this fails, then that's ok,
    we'll treat it as HTML which is fine since we know it's not a feed
    in that case. -->
    
    <ol>
     <li>Increase <var title="">pos</var> by 1.

     <li>If <span><var title="">s</var>[<var title="">pos</var>]</span> equal
      0x3E, then increase <var title="">pos</var> by 1 and jump back to step
      5 in the overall algorithm in this section.

     <li>Otherwise, return to step 1 in these substeps.
    </ol>

   <li>
    <p>If <span><var title="">s</var>[<var title="">pos</var>]</span> is 0x3F
     (ASCII "<code title="">?</code>"):</p>

    <ol>
     <li>Increase <var title="">pos</var> by 1.

     <li>If <span><var title="">s</var>[<var title="">pos</var>]</span> and
      <span><var title="">s</var>[<var title="">pos</var>+1]</span> equal
      0x3F and 0x3E respectively, then increase <var title="">pos</var> by 1
      and jump back to step 5 in the overall algorithm in this section.

     <li>Otherwise, return to step 1 in these substeps.
    </ol>

   <li>
    <p>Otherwise, if the bytes in <var title="">s</var> starting at <var
     title="">pos</var> match any of the sequences of bytes in the first
     column of the following table, then the user agent must follow the steps
     given in the corresponding cell in the second column of the same row.</p>

    <table>
     <thead>
      <tr>
       <th>Bytes in Hexadecimal

       <th>Requirement

       <th>Comment

     <tbody>
      <tr>
       <td>72 73 73

       <td>The sniffed type of the resource is "application/rss+xml"; abort
        these steps

       <td>The three ASCII characters "<code title="">rss</code>"

      <tr>
       <td>66 65 65 64

       <td>The sniffed type of the resource is "application/atom+xml"; abort
        these steps

       <td>The four ASCII characters "<code title="">feed</code>"

      <tr>
       <td>72 64 66 3A 52 44 46

       <td>Continue to the next step in this algorithm

       <td>The ASCII characters "<code title="">rdf:RDF</code>"
    </table>

    <p>If none of the byte sequences above match the bytes in <var
     title="">s</var> starting at <var title="">pos</var>, then the sniffed
     type of the resource is "text/html". Abort these steps.</p>

   <li>
    <p class=big-issue>If, before the next ">", you find two xmlns*
     attributes with http://www.w3.org/1999/02/22-rdf-syntax-ns# and
     http://purl.org/rss/1.0/ as the namespaces, then the sniffed type of the
     resource is "application/rss+xml", abort these steps. (maybe we only
     need to check for http://purl.org/rss/1.0/ actually)

   <li>
    <p>Otherwise, the sniffed type of the resource is "text/html".
  </ol>

  <p class=note>For efficiency reaons, implementations may wish to implement
   this algorithm and the algorithm for detecting the character encoding of
   HTML documents in parallel.

  <h4 id=content-type><span class=secno>4.7.5. </span>Content-Type metadata</h4>

  <p>What explicit <dfn id=content-type8 title=Content-Type>Content-Type
   metadata</dfn> is associated with the resource (the resource's type
   information) depends on the protocol that was used to fetch the resource.

  <p>For HTTP resources, only the Content-Type HTTP header contributes any
   data; the explicit type of the resource is then the value of that header,
   interpreted as described by the HTTP specifications. <a
   href="#refsHTTP">[HTTP]</a>

  <p>For resources fetched from the filesystem, user agents should use
   platform-specific conventions, e.g. operating system extension/type
   mappings.

  <p>Extensions must not be used for determining resource types for resources
   fetched over HTTP.

  <p>For resources fetched over most other protocols, e.g. FTP, there is no
   type information.

  <h3 id=user-prompts><span class=secno>4.8. </span>User prompts</h3>

  <p>The <dfn id=alert title=dom-alert><code>alert(<var
   title="">message</var>)</code></dfn> method, when invoked, must show the
   given <var title="">message</var> to the user. The user agent may make the
   method wait for the user to acknowledge the message before returning; if
   so, the user agent must <a href="#pause">pause</a> while the method is
   waiting.

  <p>The <dfn id=confirm title=dom-confirm><code>confirm(<var
   title="">message</var>)</code></dfn> method, when invoked, must show the
   given <var title="">message</var> to the user, and ask the user to respond
   with a positive or negative response. The user agent must then <a
   href="#pause">pause</a> as the the method waits for the user's response.
   If the user response positively, the method must return true, and if the
   user response negatively, the method must return false.

  <p>The <dfn id=prompt title=dom-prompt><code>prompt(<var
   title="">message</var>, <var title="">default</var>)</code></dfn> method,
   when invoked, must show the given <var title="">message</var> to the user,
   and ask the user to either respond with a string value or abort. The user
   agent must then <a href="#pause">pause</a> as the the method waits for the
   user's response. The second argument is optional. If the second argument
   (<var title="">default</var>) is present, then the response must be
   defaulted to the value given by <var title="">default</var>. If the user
   aborts, then the method must return null; otherwise, the method must
   return the string that the user responded with.

  <p>The <dfn id=print title=dom-print><code>print()</code></dfn> method,
   when invoked, should offer the user the opportunity to <a
   href="#obtain">obtain a physical form</a> of the document. The user agent
   may make the method wait for the user to either accept or decline before
   returning; if so, the user agent must <a href="#pause">pause</a> while the
   method is waiting. (This does not, of course, preclude the user agent from
   <em>always</em> offering the user with the opportunity to convert the
   document to whatever media the user might want.)

  <h3 id=scripting><span class=secno>4.9. </span>Scripting</h3>

  <h4 id=running><span class=secno>4.9.1. </span>Running executable code</h4>

  <p>Various mechanisms can cause author-provided executable code to run in
   the context of a document. These mechanisms include, but are probably not
   limited to:

  <ul>
   <li>Processing of <code><a href="#script0">script</a></code> elements.

   <li>Processing of inline <code title="javascript protocol"><a
    href="#the-javascript">javascript:</a></code> URIs (e.g. the <code
    title=attr-img-src><a href="#src">src</a></code> attribute of <code><a
    href="#img">img</a></code> elements, or an <code title="">@import</code>
    rule in a CSS <code><a href="#style">style</a></code> element block).

   <li>Event handlers, whether registered through the DOM using <code
    title="">addEventListener()</code>, by explicit <a href="#event2">event
    handler content attributes</a>, by <a href="#event3">event handler DOM
    attributes</a>, or otherwise.

   <li>Processing of technologies like XBL or SVG that have their own
    scripting features.
  </ul>

  <p>User agents may provide a mechanism to enable or disable the execution
   of author-provided code. When the user agent is configured such that
   author-provided code does not execute, or if the user agent is implemented
   so as to never execute author-provided code, it is said that <dfn
   id=scripting1>scripting is disabled</dfn>. When author-provided code
   <em>does</em> execute, <dfn id=scripting2>scripting is enabled</dfn>. A
   user agent with scripting disabled is a <a href="#non-scripted"
   title="User agents with no scripting support">user agent with no scripting
   support</a> for the purposes of conformance.

  <h4 id=origin><span class=secno>4.9.2. </span>Origin</h4>
  <!-- Hallowed are the Ori -->
  <!--
    https://bugzilla.mozilla.org/show_bug.cgi?id=346659
    https://bugzilla.mozilla.org/show_bug.cgi?id=344495
  -->

  <p>Access to certain APIs is granted or denied to scripts based on the <dfn
   id=origin0>origin</dfn> of the script and the API being accessed.

  <dl>
   <dt>If a script is in a <code><a href="#script0">script</a></code> element

   <dd>The origin of the script is the origin of the <code>Document</code> to
    which the <code><a href="#script0">script</a></code> element belongs.

   <dt>If a script is a function or other code reference created by another
    script

   <dd>The origin of the script is the origin of the script that created it.

   <dt>If a script is a <a href="#the-javascript" title="javascript
    protocol"><code title="">javascript:</code> URI</a> in an attribute

   <dd>The origin is the origin of the <code>Document</code> of the element
    on which the attribute is found.

   <dt>If a script is a <a href="#the-javascript" title="javascript
    protocol"><code title="">javascript:</code> URI</a> in a style sheet

   <dd>The origin is the origin of the <code>Document</code> to which the
    style sheet applies.

   <dt>If a script is a <a href="#the-javascript" title="javascript
    protocol"><code title="">javascript:</code> URI</a> to which a <a
    href="#browsing0">browsing context</a> is being <a href="#navigate"
    title=navigate>navigated</a>, the URI having been provided by the user
    (e.g. by using a <i>bookmarklet</i>)

   <dd>The origin is the origin of the <code>Document</code> of the <a
    href="#browsing0">browsing context</a>'s <a href="#active">active
    document</a>.

   <dt>If a script is a <a href="#the-javascript" title="javascript
    protocol"><code title="">javascript:</code> URI</a> to which a <a
    href="#browsing0">browsing context</a> is being <a href="#navigate"
    title=navigate>navigated</a>, the URI having been declared in markup

   <dd>The origin is the origin of the <code>Document</code> of the element
    (e.g. an <code><a href="#a">a</a></code> or <code><a
    href="#area">area</a></code> element) that declared the URI.

   <dt>If a script is a <a href="#the-javascript" title="javascript
    protocol"><code title="">javascript:</code> URI</a> to which a <a
    href="#browsing0">browsing context</a> is being <a href="#navigate"
    title=navigate>navigated</a>, the URI having been provided by script

   <dd>The origin is the origin of the script that provided the URI.</dd>
   <!-- ... -->
  </dl>

  <p>The origin of scripts thus comes down to finding the origin of
   <code>Document</code> objects.

  <p>The origin of a <code>Document</code> or image that was served over the
   network and whose address uses a URI scheme with a server-based naming
   authority is the tuple consisting of the &lt;scheme&gt;, &lt;host&gt;, and
   &lt;port&gt; parts of the <code>Document</code>'s full URI. <a
   href="#refsRFC2396">[RFC2396]</a> <a href="#refsRFC2732">[RFC2732]</a>

  <p>The origin of a <code>Document</code> or image that was generated from a
   <code>data:</code> URI found in another <code>Document</code> or in a
   script is the origin of the that <code>Document</code> or script.

  <p>The origin of a <code>Document</code> or image that was generated from a
   <code>data:</code> URI from another source is a globally unique identifier
   assigned when the document is created.

  <p>The origin of a <code>Document</code> or image that was generated from a
   <a href="#the-javascript" title="javascript
   protocol"><code>javascript:</code> URI</a> is the same as the origin of
   that <code>javascript:</code> URI.

  <p><dfn id=the-string>The string representing the script's domain in IDNA
   format</dfn> is obtained as follows: take the domain part of the script's
   <a href="#origin0">origin</a> tuple and apply the IDNA ToASCII algorithm
   and then the IDNA ToUnicode algorithm to each component of the domain name
   (with both the AllowUnassigned and UseSTD3ASCIIRules flags set both
   times). <a href="#refsRFC3490">[RFC3490]</a>

  <p>If ToASCII fails to convert one of the components of the string, e.g.
   because it is too long or because it contains invalid characters, or if
   the origin of the script has no domain part, then the string representing
   the script's domain in IDNA format cannot be obtained. (ToUnicode is
   defined to never fail.)

  <h4 id=security3><span class=secno>4.9.3. </span>Security exceptions</h4>

  <p class=big-issue>Define <dfn id=security8>security exception</dfn>.

  <h4 id=javascript-protocol><span class=secno>4.9.4. </span><dfn
   id=the-javascript title="javascript protocol">The <code
   title="">javascript:</code> protocol</dfn></h4>

  <p>A URI using the <code title="">javascript:</code> protocol must, if
   evaluated, be evaluated using the in-context evaluation operation defined
   for <code title="">javascript:</code> URIs. <a
   href="#refsJSURI">[JSURI]</a></p>
  <!--
JSURI: http://ietfreport.isoc.org/all-ids/draft-hoehrmann-javascript-scheme-00.txt and
       http://www.websitedev.de/ietf/draft-hoehrmann-javascript-scheme-00.txt should be as stable as it gets,
       http://ietfreport.isoc.org/idref/draft-hoehrmann-javascript-scheme/ for the latest version
-->

  <p>When a browsing context is <a href="#navigate"
   title=navigate>navigated</a> to a <code>javascript:</code> URI, and the <a
   href="#active">active document</a> of that browsing context has the same
   <a href="#origin0">origin</a> as the URI, the dereference context must be
   the <a href="#browsing0">browsing context</a> being navigated.

  <p>When a browsing context is <a href="#navigate"
   title=navigate>navigated</a> to a <code>javascript:</code> URI, and the <a
   href="#active">active document</a> of that browsing context has a
   <em>different</em> <a href="#origin0">origin</a> than the URI, the
   dereference context must be an empty object.

  <p>Otherwise, the dereference context must the <a
   href="#browsing0">browsing context</a> of the <code>Document</code> to
   which belongs the element for which the URI is being dereferenced, or to
   which the style sheet for which the URI is being dereferenced applies,
   whichever is appropriate.

  <p>URIs using the <code title="">javascript:</code> protocol should be
   evaluated when the resource for that URI is needed, unless <a
   href="#scripting1">scripting is disabled</a> or the <code>Document</code>
   corresponding to the dereference context (as defined above), if any, has
   <code title=dom-document-designMode><a
   href="#designMode">designMode</a></code> enabled.

  <p>If the dereference by-product is void (there is no return value), then
   the URI must be treated in a manner equivalent to an HTTP resource with an
   HTTP 204 No Content response.

  <p>Otherwise, the URI must be treated in a manner equivalent to an HTTP
   resource with a 200 OK response whose <a href="#content-type8"
   title=Content-Type>Content-Type metadata</a> is <code
   title="">text/html</code> and whose response body is the dereference
   by-product, converted to a string value.

  <p class=note>Certain contexts, in particular <code><a
   href="#img">img</a></code> elements, ignore the <a href="#content-type8"
   title=Content-Type>Content-Type metadata</a>.

  <div class=example>
   <p>So for example a <code title="">javascript:</code> URI for a <code
    title=attr-img-src><a href="#src">src</a></code> attribute of an <code><a
    href="#img">img</a></code> element would be evaluated in the context of
    the page as soon as the attribute is set; it would then be sniffed to
    determine the image type and decoded as an image.</p>

   <p>A <code title="">javascript:</code> URI in an <code
    title=attr-a-href>href</code> attribute of an <code><a
    href="#a">a</a></code> element would only be evaluated when the link was
    <a href="#following0" title="following hyperlinks">followed</a>.</p>

   <p>The <code title=attr-iframe-src><a href="#src1">src</a></code>
    attribute of an <code><a href="#iframe">iframe</a></code> element would
    be evaluated in the context of the <code><a
    href="#iframe">iframe</a></code>'s own <a href="#browsing0">browsing
    context</a>; once evaluated, its return value (if it was not void) would
    replace that <a href="#browsing0">browsing context</a>'s document, thus
    changing the variables visible in that <a href="#browsing0">browsing
    context</a>.</p>
  </div>

  <h4 id=events><span class=secno>4.9.5. </span>Events</h4>

  <p class=big-issue>We need to define how to handle events that are to be
   fired on a Document that is no longer the active document of its browsing
   context, and for Documents that have no browsing context. Do the events
   fire? Do the handlers in that document not fire? Do we just define
   scripting to be disabled when the document isn't active, with events still
   running as is? See also the <code><a href="#script0">script</a></code>
   element section, which says scripts don't run when the document isn't
   active.

  <h5 id=event-handler-attributes><span class=secno>4.9.5.1. </span>Event
   handler attributes</h5>

  <p><a href="#html-elements">HTML elements</a> can have <dfn id=event1>event
   handler attributes</dfn> specified. These act as bubbling event listeners
   for the element on which they are specified.

  <p>Each event handler attribute has two parts, an <a href="#event2"
   title="event handler content attributes">event handler content
   attribute</a> and an <a href="#event3" title="event handler DOM
   attributes">event handler DOM attribute</a>. Event handler attributes must
   initially be set to null. When their value changes (through the changing
   of their event handler content attribute or their event handler DOM
   attribute), they will either be null, or have an
   <code>EventListener</code> object assigned to them.

  <p>Objects other than <code>Element</code> objects, in particular <code><a
   href="#window">Window</a></code>, only have <a href="#event3" title="event
   handler DOM attributes">event handler DOM attribute</a> (since they have
   no content attributes).

  <p><dfn id=event2>Event handler content attributes</dfn>, when specified,
   must contain valid ECMAScript code matching the ECMAScript <code
   title="">FunctionBody</code> production. <a
   href="#refsECMA262">[ECMA262]</a>

  <p>When an event handler content attribute is set, its new value must be
   interpreted as the body of an anonymous function with a single argument
   called <code>event</code>, with the new function's scope chain being
   linked from the activation object of the handler, to the element, to the
   element's <code>form</code> element if it is a form control, to the
   <code>Document</code> object, to the <a href="#browsing0">browsing
   context</a> of that <code>Document</code>. The function's
   <code>this</code> parameter must be the <code>Element</code> object
   representing the element. The resulting function must then be set as the
   value of the corresponding event handler attribute, and the new value must
   be set as the value of the content attribute. If the given function body
   fails to compile, then the corresponding event handler attribute must be
   set to null instead (the content attribute must still be updated to the
   new value, though).

  <p class=note>See ECMA262 Edition 3, sections 10.1.6 and 10.2.3, for more
   details on activation objects. <a href="#refsECMA262">[ECMA262]</a>

  <p class=issue>How do we allow non-JS event handlers?

  <p><dfn id=event3>Event handler DOM attributes</dfn>, on setting, must set
   the corresponding event handler attribute to their new value, and on
   getting, must return whatever the current value of the corresponding event
   handler attribute is (possibly null).

  <p>The following are the event handler attributes that must be supported by
   all <a href="#html-elements">HTML elements</a>, as both content attributes
   and DOM attributes, and on <code><a href="#window">Window</a></code>
   objects, as DOM attributes:

  <dl>
   <dt><dfn id=onabort title=handler-onabort><code>onabort</code></dfn>

   <dd>
    <p>Must be invoked whenever an <code title=event-abort><a
     href="#abort">abort</a></code> event is targeted at or bubbles through
     the element.
   </dd>
   <!--
   <dt><dfn title="handler-onbeforecopy"><code>onbeforecopy</code></dfn></dt> -->
   <!-- widely used -->
   <!--

   <dd><p>Must be invoked whenever a <code
   title="event-beforecopy">beforecopy</code> event is targeted at or bubbles
   through the element.</p></dd>
-->

   <dt><dfn id=onbeforeunload
    title=handler-onbeforeunload><code>onbeforeunload</code></dfn>

   <dd>
    <p>Must be invoked whenever a <code
     title=event-beforeunload>beforeunload</code> event is targeted at or
     bubbles through the element.

   <dt><dfn id=onblur title=handler-onblur><code>onblur</code></dfn></dt>
   <!-- widely used -->

   <dd>
    <p>Must be invoked whenever a <code title=event-blur>blur</code> event is
     targeted at or bubbles through the element.

   <dt><dfn id=onchange title=handler-onchange><code>onchange</code></dfn></dt>
   <!-- widely used -->

   <dd>
    <p>Must be invoked whenever a <code title=event-change>change</code>
     event is targeted at or bubbles through the element.

   <dt><dfn id=onclick title=handler-onclick><code>onclick</code></dfn></dt>
   <!-- widely used -->

   <dd>
    <p>Must be invoked whenever a <code title=event-click>click</code> event
     is targeted at or bubbles through the element.

   <dt><dfn id=oncontextmenu
    title=handler-oncontextmenu><code>oncontextmenu</code></dfn></dt>
   <!-- widely used -->

   <dd>
    <p>Must be invoked whenever a <code
     title=event-contextmenu>contextmenu</code> event is targeted at or
     bubbles through the element.
   </dd>
   <!--
   <dt><dfn title="handler-oncopy"><code>oncopy</code></dfn></dt> -->
   <!-- widely used -->
   <!--

   <dd><p>Must be invoked whenever a <code
   title="event-copy">copy</code> event is targeted at or bubbles
   through the element.</p></dd>
-->

   <dt><dfn id=ondblclick
    title=handler-ondblclick><code>ondblclick</code></dfn></dt>
   <!-- widely used -->

   <dd>
    <p>Must be invoked whenever a <code title=event-dblclick>dblclick</code>
     event is targeted at or bubbles through the element.

   <dt><dfn id=ondrag title=handler-ondrag><code>ondrag</code></dfn>

   <dd>
    <p>Must be invoked whenever a <code title=event-drag><a
     href="#drag">drag</a></code> event is targeted at or bubbles through the
     element.

   <dt><dfn id=ondragend title=handler-ondragend><code>ondragend</code></dfn>

   <dd>
    <p>Must be invoked whenever a <code title=event-dragend><a
     href="#dragend">dragend</a></code> event is targeted at or bubbles
     through the element.

   <dt><dfn id=ondragenter
    title=handler-ondragenter><code>ondragenter</code></dfn>

   <dd>
    <p>Must be invoked whenever a <code title=event-dragenter><a
     href="#dragenter">dragenter</a></code> event is targeted at or bubbles
     through the element.

   <dt><dfn id=ondragleave
    title=handler-ondragleave><code>ondragleave</code></dfn>

   <dd>
    <p>Must be invoked whenever a <code title=event-dragleave><a
     href="#dragleave">dragleave</a></code> event is targeted at or bubbles
     through the element.

   <dt><dfn id=ondragover
    title=handler-ondragover><code>ondragover</code></dfn>

   <dd>
    <p>Must be invoked whenever a <code title=event-dragover><a
     href="#dragover">dragover</a></code> event is targeted at or bubbles
     through the element.

   <dt><dfn id=ondragstart
    title=handler-ondragstart><code>ondragstart</code></dfn></dt>
   <!-- widely used -->

   <dd>
    <p>Must be invoked whenever a <code title=event-dragstart><a
     href="#dragstart">dragstart</a></code> event is targeted at or bubbles
     through the element.

   <dt><dfn id=ondrop title=handler-ondrop><code>ondrop</code></dfn>

   <dd>
    <p>Must be invoked whenever a <code title=event-drop><a
     href="#drop">drop</a></code> event is targeted at or bubbles through the
     element.

   <dt><dfn id=onerror title=handler-onerror><code>onerror</code></dfn></dt>
   <!-- widely used -->

   <dd>
    <p>Must be invoked whenever an <code title=event-error><a
     href="#error1">error</a></code> event is targeted at or bubbles through
     the element.</p>

    <p class=note>The <code title=handler-onerror><a
     href="#onerror">onerror</a></code> handler is also used for <a
     href="#runtime-script-errors">reporting script errors</a>.

   <dt><dfn id=onfocus title=handler-onfocus><code>onfocus</code></dfn></dt>
   <!-- widely used -->

   <dd>
    <p>Must be invoked whenever a <code title=event-focus>focus</code> event
     is targeted at or bubbles through the element.

   <dt><dfn id=onkeydown title=handler-onkeydown><code>onkeydown</code></dfn></dt>
   <!-- widely used -->

   <dd>
    <p>Must be invoked whenever a <code title=event-keydown>keydown</code>
     event is targeted at or bubbles through the element.

   <dt><dfn id=onkeypress
    title=handler-onkeypress><code>onkeypress</code></dfn></dt>
   <!-- widely used -->

   <dd>
    <p>Must be invoked whenever a <code title=event-keypress>keypress</code>
     event is targeted at or bubbles through the element.

   <dt><dfn id=onkeyup title=handler-onkeyup><code>onkeyup</code></dfn></dt>
   <!-- widely used -->

   <dd>
    <p>Must be invoked whenever a <code title=event-keyup>keyup</code> event
     is targeted at or bubbles through the element.

   <dt><dfn id=onload title=handler-onload><code>onload</code></dfn></dt>
   <!-- widely used -->

   <dd>
    <p>Must be invoked whenever a <code title=event-load><a
     href="#load0">load</a></code> event is targeted at or bubbles through
     the element.

   <dt><dfn id=onmessage title=handler-onmessage><code>onmessage</code></dfn></dt>
   <!-- introduced for <event-source> -->

   <dd>
    <p>Must be invoked whenever a <code title=event-message><a
     href="#message">message</a></code> event is targeted at or bubbles
     through the element.

   <dt><dfn id=onmousedown
    title=handler-onmousedown><code>onmousedown</code></dfn></dt>
   <!-- widely used -->

   <dd>
    <p>Must be invoked whenever a <code
     title=event-mousedown>mousedown</code> event is targeted at or bubbles
     through the element.

   <dt><dfn id=onmousemove
    title=handler-onmousemove><code>onmousemove</code></dfn></dt>
   <!-- widely used -->

   <dd>
    <p>Must be invoked whenever a <code
     title=event-mousemove>mousemove</code> event is targeted at or bubbles
     through the element.

   <dt><dfn id=onmouseout
    title=handler-onmouseout><code>onmouseout</code></dfn></dt>
   <!-- widely used -->

   <dd>
    <p>Must be invoked whenever a <code title=event-mouseout>mouseout</code>
     event is targeted at or bubbles through the element.

   <dt><dfn id=onmouseover
    title=handler-onmouseover><code>onmouseover</code></dfn></dt>
   <!-- widely used -->

   <dd>
    <p>Must be invoked whenever a <code
     title=event-mouseover>mouseover</code> event is targeted at or bubbles
     through the element.

   <dt><dfn id=onmouseup title=handler-onmouseup><code>onmouseup</code></dfn></dt>
   <!-- widely used -->

   <dd>
    <p>Must be invoked whenever a <code title=event-mouseup>mouseup</code>
     event is targeted at or bubbles through the element.

   <dt><dfn id=onmousewheel
    title=handler-onmousewheel><code>onmousewheel</code></dfn></dt>
   <!-- widely used -->

   <dd>
    <p>Must be invoked whenever a <code
     title=event-mousewheel>mousewheel</code> event is targeted at or bubbles
     through the element.
   </dd>
   <!--
   <dt><dfn title="handler-onpaste"><code>onpaste</code></dfn></dt> -->
   <!-- widely used -->
   <!--

   <dd><p>Must be invoked whenever a <code
   title="event-paste">paste</code> event is targeted at or bubbles
   through the element.</p></dd>
-->

   <dt><dfn id=onresize title=handler-onresize><code>onresize</code></dfn></dt>
   <!-- widely used -->

   <dd>
    <p>Must be invoked whenever a <code title=event-resize>resize</code>
     event is targeted at or bubbles through the element.
   </dd>
   <!-- XXX should define when it fires -->

   <dt><dfn id=onscroll title=handler-onscroll><code>onscroll</code></dfn></dt>
   <!-- widely used -->

   <dd>
    <p>Must be invoked whenever a <code title=event-scroll>scroll</code>
     event is targeted at or bubbles through the element.
   </dd>
   <!-- XXX should define when it fires -->

   <dt><dfn id=onselect title=handler-onselect><code>onselect</code></dfn></dt>
   <!-- widely used -->

   <dd>
    <p>Must be invoked whenever a <code title=event-select><a
     href="#select">select</a></code> event is targeted at or bubbles through
     the element.
   </dd>
   <!-- XXX should define when it fires -->
   <!--XXX
   <dt><dfn title="handler-onselectstart"><code>onselectstart</code></dfn></dt> -->
   <!-- widely used -->
   <!--

   <dd><p>Must be invoked whenever a <code
   title="event-selectstart">selectstart</code> event is targeted at or bubbles
   through the element.</p></dd>
-->
   <!-- XXX should define when it fires -->

   <dt><dfn id=onsubmit title=handler-onsubmit><code>onsubmit</code></dfn></dt>
   <!-- widely used -->

   <dd>
    <p>Must be invoked whenever a <code title=event-submit>submit</code>
     event is targeted at or bubbles through the element.

   <dt><dfn id=onunload title=handler-onunload><code>onunload</code></dfn></dt>
   <!-- widely used -->

   <dd>
    <p>Must be invoked whenever an <code title=event-unload>unload</code>
     event is targeted at or bubbles through the element.
   </dd>
   <!-- XXX need to fire this -->
  </dl>

  <p>When an event handler attribute is invoked, its argument must be set to
   the <code>Event</code> object of the event in question. If the function
   returns the exact boolean value false, the event's
   <code>preventDefault()</code> method must then invoked. Exception: for
   historical reasons, for the HTML <code>mouseover</code> event, the
   <code>preventDefault()</code> method must be called when the function
   returns true instead.</p>
  <!-- IE actually uncancels the event if the function returns true -->

  <p>When <a href="#scripting1">scripting is disabled</a>, event handler
   attributes must do nothing.

  <p>When <a href="#scripting2">scripting is enabled</a>, all event handler
   attributes on an element, whether set to null or to a function, must be
   registered as event listeners on the element, as if the <code
   title=dom-EventTarget-addEventListenerNS>addEventListenerNS()</code>
   method on the <code>Element</code> object's <code>EventTarget</code>
   interface had been invoked when the element was created, with the event
   type (<code title=dom-event-type>type</code> argument) equal to the type
   described for the event handler attribute in the list above, the namespace
   (<code title=dom-event-namespaceURI>namespaceURI</code> argument) set to
   null, the listener set to be a target and bubbling phase listener (<code
   title=dom-event-useCapture>useCapture</code> argument set to false), the
   event group set to the default group (<code
   title=dom-event-evtGroup>evtGroup</code> argument set to null), and the
   event listener itself (<code title=dom-event-listener>listener</code>
   argument) set to do nothing while the event handler attribute is null, and
   set to invoke the function associated with the event handler attribute
   otherwise.

  <h5 id=event><span class=secno>4.9.5.2. </span>Event firing</h5>

  <p class=big-issue>maybe this should be moved higher up (terminology?
   conformance? DOM?)

  <p>Certain operations and methods are defined as firing events on elements.
   For example, the <code title=dom-click><a href="#click">click()</a></code>
   method on the <code><a href="#htmlelement">HTMLElement</a></code>
   interface is defined as firing a <code title=event-click>click</code>
   event on the element. <a href="#refsDOM3EVENTS">[DOM3EVENTS]</a>

  <p><dfn id=firing title="fire a click event">Firing a <code
   title=event-click>click</code> event</dfn> means that a <a
   href="http://www.w3.org/TR/DOM-Level-3-Events/events.html#event-click"><code>click</code></a>
   event with no namespace, which bubbles and is cancelable, and which uses
   the <code>MouseEvent</code> interface, must be dispatched at the given
   element. The event object must have its <code title="">screenX</code>,
   <code title="">screenY</code>, <code title="">clientX</code>, <code
   title="">clientY</code>, and <code title="">button</code> attributes set
   to 0, its <code title="">ctrlKey</code>, <code title="">shiftKey</code>,
   <code title="">altKey</code>, and <code title="">metaKey</code> attributes
   set according to the current state of the key input device, if any (false
   for any keys that are not available), its <code title="">detail</code>
   attribute set to 1, and its <code title="">relatedTarget</code> attribute
   set to null. The <code title="">getModifierState()</code> method on the
   object must return values appropriately describing the state of the key
   input device at the time the event is created.

  <p><dfn id=firing0 title="fire a change event">Firing a <code
   title=event-change>change</code> event</dfn> means that a <a
   href="http://www.w3.org/TR/DOM-Level-3-Events/events.html#event-change"><code>change</code></a>
   event with no namespace, which bubbles but is not cancelable, and which
   uses the <code>Event</code> interface, must be dispatched at the given
   element. The event object must have its <code title="">detail</code>
   attribute set to 0.

  <p><dfn id=firing1 title="fire a contextmenu event">Firing a <code
   title=event-contextmenu>contextmenu</code> event</dfn> means that a <code
   title=event-contextmenu>contextmenu</code> event with no namespace, which
   bubbles and is cancelable, and which uses the <code>Event</code>
   interface, must be dispatched at the given element. The event object must
   have its <code title="">detail</code> attribute set to 0.

  <p><dfn id=firing2 title="fire a simple event">Firing a simple event called
   <var title="">e</var></dfn> means that an event with the name <var
   title="">e</var>, with no namespace, which does not bubble but is
   cancelable, and which uses the <code>Event</code> interface, must be
   dispatched at the given element.

  <p><dfn id=firing3 title="fire a show event">Firing a <code
   title=event-show>show</code> event</dfn> means <a href="#firing2"
   title="fire a simple event">firing a simple event called <code
   title=event-show>show</code></a>. <dfn id=firing4 title="fire a load
   event">Firing a <code title=event-load>load</code> event</dfn> means <a
   href="#firing2" title="fire a simple event">firing a simple event called
   <code title=event-load>load</code></a>. <!--<dfn title="fire a
  DOMContentLoaded event">Firing a <code
  title="event-DOMContentLoaded">DOMContentLoaded</code> event</dfn>
  means <span title="fire a simple event">firing a simple event called
  <code
  title="event-DOMContentLoaded">DOMContentLoaded</code></span>.-->
   <dfn id=firing5 title="fire an error event">Firing an <code
   title=event-error>error</code> event</dfn> means <a href="#firing2"
   title="fire a simple event">firing a simple event called <code
   title=event-error>error</code></a>.</p>
  <!-- XXX need to define the dispatching of DOMActivate -->

  <p class=big-issue><dfn id=firing6 title="fire a progress event">Firing a
   progress event called <var title="">e</var></dfn> means something that
   hasn't yet been defined, in the <a href="#refsPROGRESS">[PROGRESS]</a>
   spec.

  <p>The default action of these event is to do nothing unless otherwise
   stated.

  <p class=big-issue>If you dispatch a custom "click" event at an element
   that would normally have default actions, should they get triggered? If
   so, we need to go through the entire spec and make sure that any default
   actions are defined in terms of <em>any</em> event of the right type on
   that element, not those that are dispatched in expected ways.

  <h5 id=events0><span class=secno>4.9.5.3. </span>Events and the <code><a
   href="#window">Window</a></code> object</h5>

  <p>When an event is dispatched at a DOM node in a <code>Document</code> in
   a <a href="#browsing0">browsing context</a>, if the event is not a <code
   title=event-load><a href="#load0">load</a></code> event, the user agent
   must also dispatch the event to the <code><a
   href="#window">Window</a></code>, as follows:

  <ol>
   <li>In the capture phase, the event must be dispatched to the <code><a
    href="#window">Window</a></code> object before being dispatched to any of
    the nodes.

   <li>In the bubble phase, the event must be dispatched to the <code><a
    href="#window">Window</a></code> object at the end of the phase, unless
    bubbling has been prevented.
  </ol>

  <h5 id=runtime-script-errors><span class=secno>4.9.5.4. </span>Runtime
   script errors</h5>

  <p><em>This section only applies to user agents that support scripting in
   general and ECMAScript in particular.</em>

  <p>Whenever a runtime script error occurs in one of the scripts associated
   with the document, the value of the <code title=handler-onerror><a
   href="#onerror">onerror</a></code> <span>event handler DOM
   attribute</span> of the <code><a href="#window">Window</a></code> object
   must be processed, as follows:

  <dl class=switch>
   <dt>If the value is a function

   <dd>
    <p>The function referenced by the <code title=handler-onerror><a
     href="#onerror">onerror</a></code> attribute must be invoked with three
     arguments, before notifying the user of the error.</p>

    <p>The three arguments passed to the function are all
     <code>DOMString</code>s; the first must give the message that the UA is
     considering reporting, the second must give the URI to the resource in
     which the error occured, and the third must give the line number in that
     resource on which the error occured.</p>

    <p>If the function returns false, then the error should not be reported
     to the user. Otherwise, if the function returns another value (or does
     not return at all), the error should be reported to the user.</p>

    <p>Any exceptions thrown or errors caused by this function must be
     reported to the user immediately after the error that the function was
     called for, without calling the function again.</p>

   <dt>If the value is <code>null</code>

   <dd>
    <p>The error should not reported to the user.</p>

   <dt>If the value is anything else

   <dd>
    <p>The error should be reported to the user.</p>
  </dl>

  <p>The initial value of <code title=handler-onerror><a
   href="#onerror">onerror</a></code> must be <code>undefined</code>.

  <h3 id=browser><span class=secno>4.10. </span>Browser state</h3>

  <p>The <dfn id=navigator title=dom-navigator><code>navigator</code></dfn>
   attribute of the <code><a href="#window">Window</a></code> interface must
   return an instance of the <code><a
   href="#clientinformation">ClientInformation</a></code> interface, which
   represents the identity and state of the user agent (the client), and
   allows Web pages to register themselves as potential protocol and content
   handlers:

  <pre
   class=idl>interface <dfn id=clientinformation>ClientInformation</dfn> {
  readonly attribute boolean <a href="#navigator.online" title=dom-navigator-onLine>onLine</a>;
  void <a href="#registerprotocolhandler" title=dom-navigator-registerProtocolHandler>registerProtocolHandler</a>(in DOMString protocol, in DOMString uri, in DOMString title);
  void <a href="#registercontenthandler" title=dom-navigator-registerContentHandler>registerContentHandler</a>(in DOMString mimeType, in DOMString uri, in DOMString title);
<!-- XXX there are other attributes! -->};</pre>
  <!-- also, see window.external.AddSearchProvider() and similar DOM APIs from IE -->

  <h4 id=offline><span class=secno>4.10.1. </span>Offline Web applications</h4>

  <p>The <dfn id=navigator.online
   title=dom-navigator-onLine><code>navigator.onLine</code></dfn> attribute
   must return false if the user agent will not contact the network when the
   user follows links or when a script requests a remote page (or knows that
   such an attempt would fail), and must return true otherwise.

  <p>The <dfn id=offline0 title=event-offline><code>offline</code></dfn>
   event must be fired when the value of the <code
   title=dom-navigator-onLine><a
   href="#navigator.online">navigator.onLine</a></code> attribute of the
   <code><a href="#window">Window</a></code> changes from true to false.

  <p>The <dfn id=online title=event-online><code>online</code></dfn> event
   must be fired when the value of the <code title=dom-navigator-onLine><a
   href="#navigator.online">navigator.onLine</a></code> attribute of the
   <code><a href="#window">Window</a></code> changes from false to true.

  <p>These events are in no namespace, do bubble, are not cancelable, have no
   default action, and use the normal <code>Event</code> interface. They must
   be fired on <a href="#the-body0">the body element</a>. (As the events
   bubble, they will reach the <code><a href="#window">Window</a></code>
   object.)</p>
  <!-- XXX ononline onoffline need to be defined -->

  <h4 id=custom-handlers><span class=secno>4.10.2. </span>Custom protocol and
   content handlers</h4>

  <p>The <dfn id=registerprotocolhandler
   title=dom-navigator-registerProtocolHandler><code>registerProtocolHandler()</code></dfn>
   method allows Web sites to register themselves as possible handlers for
   particular protocols. For example, an online fax service could register
   itself as a handler of the <code>fax:</code> protocol (<a
   href="#refsRFC2806">[RFC2806]</a>), so that if the user clicks on such a
   link, he is given the opportunity to use that Web site. Analogously, the
   <dfn id=registercontenthandler
   title=dom-navigator-registerContentHandler><code>registerContentHandler()</code></dfn>
   method allows Web sites to register themselves as possible handlers for
   content in a particular MIME type. For example, the same online fax
   service could register itself as a handler for <code>image/g3fax</code>
   files (<a href="#refsRFC1494">[RFC1494]</a>), so that if the user has no
   native application capable of handling G3 Facsimile byte streams, his Web
   browser can instead suggest he use that site to view the image.

  <p>User agents may, within the constraints described in this section, do
   whatever they like when the methods are called. A UA could, for instance,
   prompt the user and offer the user the opportunity to add the site to a
   shortlist of handlers, or make the handlers his default, or cancel the
   request. UAs could provide such a UI through modal UI or through a
   non-modal transient notification interface. UAs could also simply silently
   collect the information, providing it only when relevant to the user.

  <p>There is <a href="#sample-handler-impl">an example of how these methods
   could be presented to the user</a> below.

  <p>The arguments to the methods have the following meanings:

  <dl>
   <dt><var title="">protocol</var> (<code
    title=dom-navigator-registerProtocolHandler><a
    href="#registerprotocolhandler">registerProtocolHandler()</a></code>
    only)

   <dd>
    <p>A scheme, such as <code>ftp</code> or <code>fax</code>. The scheme
     must be treated case-insensitively by user agents for the purposes of
     comparing with the scheme part of URIs that they consider against the
     list of registered handlers.</p>

    <p>The <var title="">protocol</var> value, if it contains a colon (as in
     "<code>ftp:</code>"), will never match anything, since schemes don't
     contain colons.</p>

   <dt><var title="">mimeType</var> (<code
    title=dom-navigator-registerContentHandler><a
    href="#registercontenthandler">registerContentHandler()</a></code> only)

   <dd>
    <p>A MIME type, such as <code>model/vrml</code> or
     <code>text/richtext</code>. The MIME type must be treated
     case-insensitively by user agents for the purposes of comparing with
     MIME types of documents that they consider against the list of
     registered handlers.</p>

    <p>User agents must compare the given values only to the MIME
     type/subtype parts of content types, not to the complete type including
     parameters. Thus, if <var title="">mimeType</var> values passed to this
     method include characters such as commas or whitespace, or include MIME
     parameters, then the handler being registered will never be used.</p>

   <dt><var title="">uri</var>

   <dd>
    <p>The URI of the page that will handle the requests. When the user agent
     uses this URI, it must replace the first occurrence of the exact literal
     string "<code>%s</code>" with an escaped version of the URI of the
     content in question (as defined below), and then fetch the resulting URI
     using the GET method (or equivalent for non-HTTP URIs).</p>

    <p>To get the escaped version of the URI, first, the domain part of the
     URI (if any) must be converted to its punycode representation, and then,
     every character in the URI that is not in the ranges given in the next
     paragraph must be replaced by its UTF-8 byte representation, each byte
     being represented by a U+0025 (%) character and two digits in the range
     U+0030 (0) to U+0039 (9) and U+0041 (A) to U+0046 (F) giving the
     hexadecimal representation of the byte.</p>

    <p>The ranges of characters that must not be escaped are: U+002D (-),
     U+002E (.), U+0030 (0) to U+0039 (9), U+0041 (A) to U+005A (Z), U+005F
     (_), U+0061 (a) to U+007A (z), and U+007E (~).</p>
    <!-- XXX move that to a common algorithms section if any other
    part of the spec needs it -->
    
    <div class=example>
     <p>If the user had visited a site that made the following call:</p>

     <pre>navigator.registerContentHandler('application/x-soup', 'http://example.com/soup?url=%s', 'SoupWeb&trade;')</pre>

     <p>...and then clicked on a link such as:</p>

     <pre>&lt;a href="http://www.example.net/chickenk&#xEF;wi.soup">Download our Chicken Kiwi soup!&lt;/a></pre>

     <p>...then, assuming this <code>chickenkiwi.soup</code> file was served
      with the MIME type <code>application/x-soup</code>, the UA might
      instead navigate to the following URI:</p>

     <pre>http://example.com/soup?url=http%3A%2F%2Fwww.example.net%2Fchickenk%C3%AFwi.soup</pre>

     <p>This site could then fetch the <code>chickenkiwi.soup</code> file and
      do whatever it is that it does with soup (synthesise it and ship it to
      the user, or whatever).</p>
    </div>

   <dt><var title="">title</var>

   <dd>
    <p>A descriptive title of the handler, which the UA might use to remind
     the user what the site in question is.</p>
  </dl>

  <p>User agents should raise <a href="#security8" title="security
   exception">security exceptions</a> if the methods are called with <var
   title="">protocol</var> or <var title="">mimeType</var> values that the UA
   deems to be "privileged". For example, a site attempting to register a
   handler for <code>http</code> URIs or <code>text/html</code> content in a
   Web browser would likely cause an exception to be raised.

  <p>User agents must raise a <code>SYNTAX_ERR</code> exception if the <var
   title="">uri</var> argument passed to one of these methods does not
   contain the exact literal string "<code>%s</code>".

  <p>User agents must not raise any other exceptions (other than
   binding-specific exceptions, such as for an incorrect number of arguments
   in an ECMAScript implementation).

  <p>This section does not define how the pages registered by these methods
   are used, beyond the requirements on how to process the <var
   title="">uri</var> value (see above). To some extent, the <span
   title="navigating across documents">processing model for navigating across
   documents</span> defines some cases where these methods are relevant, but
   in general UAs may use this information wherever they would otherwise
   consider handing content to native plugins or helper applications.

  <p>UAs must not use registered content handlers to handle content that was
   returned as part of a non-GET transaction (or rather, as part of any
   non-idempotent transaction), as the remote site would not be able to fetch
   the same data.

  <h5 id=security4><span class=secno>4.10.2.1. </span>Security and privacy</h5>

  <p>These mechanisms can introduce a number of concerns, in particular
   privacy concerns.

  <p><strong>Hijacking all Web usage.</strong> User agents should not allow
   protocols that are key to its normal operation, such as <code>http</code>
   or <code>https</code>, to be rerouted through third-party sites. This
   would allow a user's activities to be trivially tracked, and would allow
   user information, even in secure connections, to be collected.

  <p><strong>Hijacking defaults.</strong> It is strongly recommended that
   user agents do not automatically change any defaults, as this could lead
   the user to send data to remote hosts that the user is not expecting. New
   handlers registering themselves should never automatically cause those
   sites to be used.

  <p><strong>Registration spamming.</strong> User agents should consider the
   possibility that a site will attempt to register a large number of
   handlers, possibly from multiple domains (e.g. by redirecting through a
   series of pages each on a different domain, and each registering a handler
   for <code>video/mpeg</code> &mdash; analogous practices abusing other Web
   browser features have been used by pornography Web sites for many years).
   User agents should gracefully handle such hostile attempts, protecting the
   user.

  <p><strong>Misleading titles.</strong> User agents should not rely wholy on
   the <var title="">title</var> argument to the methods when presenting the
   registered handlers to the user, since sites could easily lie. For
   example, a site <code>hostile.example.net</code> could claim that it was
   registering the "Cuddly Bear Happy Content Handler". User agents should
   therefore use the handler's domain in any UI along with any title.

  <p><strong>Hostile handler metadata.</strong> User agents should protect
   against typical attacks against strings embedded in their interface, for
   example ensuring that markup or escape characters in such strings are not
   executed, that null bytes are properly handled, that over-long strings do
   not cause crashes or buffer overruns, and so forth.

  <p><strong>Leaking Intranet URIs.</strong> The mechanism described in this
   section can result in secret Intranet URIs being leaked, in the following
   manner:

  <ol>
   <li>The user registers a third-party content handler as the default
    handler for a content type.

   <li>The user then browses his corporate Intranet site and accesses a
    document that uses that content type.

   <li>The user agent contacts the third party and hands the third party the
    URI to the Intranet content.
  </ol>

  <p>No actual confidential file data is leaked in this manner, but the URIs
   themselves could contain confidential information. For example, the URI
   could be
   <code>https://www.corp.example.com/upcoming-aquisitions/samples.egf</code>,
   which might tell the third party that Example Corporation is intending to
   merge with Samples LLC. Implementors might wish to consider allowing
   administrators to disable this feature for certain subdomains, content
   types, or protocols.

  <p><strong>Leaking secure URIs.</strong> User agents should not send HTTPS
   URIs to third-party sites registered as content handlers, in the same way
   that user agents do not send <code>Referer</code> headers from secure
   sites to third-party sites.

  <p><strong>Leaking credentials.</strong> User agents must never send
   username or password information in the URIs that are escaped and included
   sent to the handler sites. User agents may even avoid attempting to pass
   to Web-based handlers the URIs of resources that are known to require
   authentication to access, as such sites would be unable to access the
   resources in question without prompting the user for credentials
   themselves (a practice that would require the user to know whether to
   trust the third-party handler, a decision many users are unable to make or
   even understand).

  <h5 id=sample-handler-impl><span class=secno>4.10.2.2. </span>Sample user
   interface</h5>

  <p><em>This section is non-normative.</em>

  <p>A simple implementation of this feature for a desktop Web browser might
   work as follows.

  <p>The <code title=dom-navigator-registerProtocolHandler><a
   href="#registerprotocolhandler">registerProtocolHandler()</a></code>
   method could display a modal dialog box:

  <pre>||[ Protocol Handler Registration ]|||||||||||||||||||||||||||
|                                                            |
| This Web page:                                             |
|                                                            |
|    Kittens at work                                         |
|    http://kittens.example.org/                             |
|                                                            |
| ...would like permission to handle the protocol "x-meow:"  |
| using the following Web-based application:                 |
|                                                            |
|    Kittens-at-work displayer                               |
|    http://kittens.example.org/?show=%s                     |
|                                                            |
| Do you trust the administrators of the "kittens.example.   |
| org" domain?                                               |
|                                                            |
|              ( Trust kittens.example.org )  (( Cancel ))   |
|____________________________________________________________|</pre>

  <p>...where "Kittens at work" is the title of the page that invoked the
   method, "http://kittens.example.org/" is the URI of that page, "x-meow" is
   the string that was passed to the <code
   title=dom-navigator-registerProtocolHandler><a
   href="#registerprotocolhandler">registerProtocolHandler()</a></code>
   method as its first argument (<var title="">protocol</var>),
   "http://kittens.example.org/?show=%s" was the second argument (<var
   title="">uri</var>), and "Kittens-at-work displayer" was the third
   argument (<var title="">title</var>).

  <p>If the user clicks the Cancel button, then nothing further happens. If
   the user clicks the "Trust" button, then the handler is remembered.

  <p>When the user then attempts to fetch a URI that uses the "x-meow:"
   scheme, then it might display a dialog as follows:

  <pre>||[ Unknown Protocol ]||||||||||||||||||||||||||||||||||||||||
|                                                            |
| You have attempted to access:                              |
|                                                            |
|    x-meow:S2l0dGVucyBhcmUgdGhlIGN1dGVzdCE%3D               |
|                                                            |
| How would you like FerretBrowser to handle this resource?  |
|                                                            |
|  (o) Contact the FerretBrowser plugin registry to see if   |
|      there is an official way to handle this resource.     |
|                                                            |
|  ( ) Pass this URI to a local application:                 |
|      [ /no application selected/             ] ( Choose )  |
|                                                            |
|  ( ) Pass this URI to the "Kittens-at-work displayer"      |
|      application at "kittens.example.org".                 |
|                                                            |
|  [ ] Always do this for resources using the "x-meow"       |
|      protocol in future.                                   |
|                                                            |
|                                     ( Ok )  (( Cancel ))   |
|____________________________________________________________|</pre>

  <p>...where the third option is the one that was primed by the site
   registering itself earlier.

  <p>If the user does select that option, then the browser, in accordance
   with the requirements described in the previous two sections, will
   redirect the user to
   "http://kittens.example.org/?show=x-meow%3AS2l0dGVucyBhcmUgdGhlIGN1dGVzdCE%253D".

  <p>The <code title=dom-navigator-registerContentHandler><a
   href="#registercontenthandler">registerContentHandler()</a></code> method
   would work equivalently, but for unknown MIME types instead of unknown
   protocols.

  <h3 id=storage><span class=secno>4.11. </span>Client-side session and
   persistent storage of name/value pairs</h3>

  <h4 id=introduction0><span class=secno>4.11.1. </span>Introduction</h4>

  <p><em>This section is non-normative.</em>

  <p>This specification introduces two related mechanisms, similar to HTTP
   session cookies <a href="#refsRFC2965">[RFC2965]</a>, for storing
   structured data on the client side.

  <p>The first is designed for scenarios where the user is carrying out a
   single transaction, but could be carrying out multiple transactions in
   different windows at the same time.

  <p>Cookies don't really handle this case well. For example, a user could be
   buying plane tickets in two different windows, using the same site. If the
   site used cookies to keep track of which ticket the user was buying, then
   as the user clicked from page to page in both windows, the ticket
   currently being purchased would "leak" from one window to the other,
   potentially causing the user to buy two tickets for the same flight
   without really noticing.

  <p>To address this, this specification introduces the <code
   title=dom-sessionStorage><a
   href="#sessionstorage">sessionStorage</a></code> DOM attribute. Sites can
   add data to the session storage, and it will be accessible to any page
   from that domain opened in that window.

  <div class=example>
   <p>For example, a page could have a checkbox that the user ticks to
    indicate that he wants insurance:</p>

   <pre>&lt;label>
 &lt;input type="checkbox" onchange="sessionStorage.insurance = checked">
 I want insurance on this trip.
&lt;/label></pre>

   <p>A later page could then check, from script, whether the user had
    checked the checkbox or not:</p>

   <pre>if (sessionStorage.insurance) { ... }</pre>

   <p>If the user had multiple windows opened on the site, each one would
    have its own individual copy of the session storage object.</p>
  </div>
  <!--

   sessionStorage.flightDeparture = 'OSL';
   sessionStorage.flightArrival = 'NYC';

   for (var i in forms[0].elements)
      sessionStorage["data_" + i.name] = i.value;

   if (!sessionStorage[documents])
     sessionStorage[documents] = {};
   sessionStorage[documents][filename] = <document/>;

  -->

  <p>The second storage mechanism is designed for storage that spans multiple
   windows, and lasts beyond the current session. In particular, Web
   applications may wish to store megabytes of user data, such as entire
   user-authored documents or a user's mailbox, on the clientside for
   performance reasons.

  <p>Again, cookies do not handle this case well, because they are
   transmitted with every request.

  <p>The <code title=dom-globalStorage><a
   href="#globalstorage">globalStorage</a></code> DOM attribute is used to
   access the global storage areas.

  <div class=example>
   <p>The site at example.com can display a count of how many times the user
    has loaded its page by putting the following at the bottom of its page:</p>

   <pre>&lt;p>
  You have viewed this page
  &lt;span id="count">an untold number of&lt;/span>
  time(s).
&lt;/p>
&lt;script>
  var storage = globalStorage['example.com'];
  if (!storage.pageLoadCount)
    storage.pageLoadCount = 0;
  storage.pageLoadCount = parseInt(storage.pageLoadCount, 10) + 1;
  document.getElementById('count').textContent = storage.pageLoadCount;
&lt;/script></pre>
  </div>

  <p>Each domain and each subdomain has its own separate storage area.
   Subdomains can access the storage areas of parent domains, and domains can
   access the storage areas of subdomains.

  <ul class=brief>
   <li><code>globalStorage['']</code> is accessible to all domains.

   <li><code>globalStorage['com']</code> is accessible to all .com domains

   <li><code>globalStorage['example.com']</code> is accessible to example.com
    and any of its subdomains

   <li><code>globalStorage['www.example.com']</code> is accessible to
    www.example.com and example.com, but not www2.example.com.
  </ul>

  <p>Storage areas (both session storage and global storage) store strings.
   To store structured data in a storage area, you must first convert it to a
   string.

  <h4 id=the-storage><span class=secno>4.11.2. </span>The <code><a
   href="#storage2">Storage</a></code> interface</h4>

  <pre class=idl>
interface <dfn id=storage2>Storage</dfn> {
  readonly attribute unsigned long <a href="#length7" title=dom-Storage-length>length</a>;
  DOMString <a href="#keyn" title=dom-Storage-key>key</a>(in unsigned long index);
  <a href="#storageitem">StorageItem</a> <a href="#getitem" title=dom-Storage-getItem>getItem</a>(in DOMString key);
  void <a href="#setitem" title=dom-Storage-setItem>setItem</a>(in DOMString key, in DOMString data);
  void <a href="#removeitem" title=dom-Storage-removeItem>removeItem</a>(in DOMString key);
};</pre>

  <p>Each <code><a href="#storage2">Storage</a></code> object provides access
   to a list of key/value pairs, which are sometimes called items. Keys are
   strings, and any string (including the empty string) is a valid key.
   Values are strings with associated metadata, represented by <code><a
   href="#storageitem">StorageItem</a></code> objects.

  <p>Each <code><a href="#storage2">Storage</a></code> object is associated
   with a list of key/value pairs when it is created, as defined in the
   sections on the <code title=dom-sessionStorage><a
   href="#sessionstorage">sessionStorage</a></code> and <code
   title=dom-globalStorage><a href="#globalstorage">globalStorage</a></code>
   attributes. Multiple separate objects implementing the <code><a
   href="#storage2">Storage</a></code> interface can all be associated with
   the same list of key/value pairs simultaneously.

  <p>Key/value pairs have associated metadata. In particular, a key/value
   pair can be marked as either "safe only for secure content", or as "safe
   for both secure and insecure content".

  <p>A key/value pair is <dfn id=accessible title="accessible
   keys">accessible</dfn> if either it is marked as "safe for both secure and
   insecure content", or it is marked as "safe only for secure content" and
   the script in question is running in a <span>secure browsing
   context</span><!-- XXX xref -->.

  <p>The <dfn id=length7 title=dom-Storage-length><code>length</code></dfn>
   attribute must return the number of key/value pairs currently present and
   <a href="#accessible" title="accessible keys">accessible</a> in the list
   associated with the object.

  <p>The <dfn id=keyn title=dom-Storage-key><code>key(<var
   title="">n</var>)</code></dfn> method must return the name of the <var
   title="">n</var>th <span>accessible</span> key in the list. The order of
   keys is user-agent defined, but must be consistent within an object
   between changes to the number of keys. (Thus, <a href="#setitem"
   title=dom-Storage-setItem>adding</a> or <a href="#removeitem"
   title=dom-Storage-removeItem>removing</a> a key may change the order of
   the keys, but merely changing the value of an existing key must not.)
   <!--The order of keys may differ between instances of the
  <code>Storage</code> interface accessing the same list. [removed for
  now for clarity, but if people ask, put it back. this is part of the
  spec.]-->
   If <var title="">n</var> is less than zero or greater than or equal to the
   number of key/value pairs in the object, then this method must raise an
   <code>INDEX_SIZE_ERR</code> exception.

  <p>The <dfn id=getitem title=dom-Storage-getItem><code>getItem(<var
   title="">key</var>)</code></dfn> method must return the <code><a
   href="#storageitem">StorageItem</a></code> object representing the
   key/value pair with the given <var title="">key</var>. If the given <var
   title="">key</var> does not exist in the list associated with the object,
   or is not <span>accessible</span>, then this method must return null.
   Subsequent calls to this method with the same key from scripts running in
   the same <span>security context</span> must return the same instance of
   the <code><a href="#storageitem">StorageItem</a></code> interface. (Such
   instances must not be shared across security contexts, though.)</p>
  <!-- XXX define security context -->

  <p>The <dfn id=setitem title=dom-Storage-setItem><code>setItem(<var
   title="">key</var>, <var title="">value</var>)</code></dfn> method must
   first check if a key/value pair with the given <var title="">key</var>
   already exists in the list associated with the object.

  <p>If it does not, then a new key/value pair must be added to the list,
   with the given <var title="">key</var> and <var title="">value</var>, such
   that any current or future <code><a
   href="#storageitem">StorageItem</a></code> objects referring to this
   key/value pair will return the value given in the <var
   title="">value</var> argument. If the script setting the value is running
   in a <span>secure browsing context</span>, then the key/value pair must be
   marked as "safe only for secure content", otherwise it must be marked as
   "safe for both secure and insecure content".

  <p>If the given <var title="">key</var> <em>does</em> exist in the list,
   then, if the key/value pair with the given <var title="">key</var> is
   <span>accessible</span>, it must have its value updated so that any
   current or future <code><a href="#storageitem">StorageItem</a></code>
   objects referring to this key/value pair will return the value given in
   the <var title="">value</var> argument. If it is <em>not</em>
   <span>accessible</span>, the method must raise a <a
   href="#security8">security exception</a>.

  <p>When the <code title=dom-Storage-setItem><a
   href="#setitem">setItem()</a></code> method is successfully invoked (i.e.
   when it doesn't raise an exception), events are fired on other <code><a
   href="#htmldocument">HTMLDocument</a></code> objects that can access the
   newly stored data, as defined in the sections on the <code
   title=dom-sessionStorage><a
   href="#sessionstorage">sessionStorage</a></code> and <code
   title=dom-globalStorage><a href="#globalstorage">globalStorage</a></code>
   attributes.</p>
  <!--
  not normative, see the sections below for the normative statement
  -->

  <p>The <dfn id=removeitem
   title=dom-Storage-removeItem><code>removeItem(<var
   title="">key</var>)</code></dfn> method must cause the key/value pair with
   the given <var title="">key</var> to be removed from the list associated
   with the object, if it exists and is <span>accessible</span>. If no item
   with that key exists, the method must do nothing. If an item with that key
   exists but is not <span>accessible</span>, the method must raise a <a
   href="#security8">security exception</a>.

  <p>The <code title=dom-Storage-setItem><a
   href="#setitem">setItem()</a></code> and <code
   title=dom-Storage-removeItem><a href="#removeitem">removeItem()</a></code>
   methods must be atomic with respect to failure. That is, changes to the
   data storage area must either be successful, or the data storage area must
   not be changed at all.

  <p>In the ECMAScript DOM binding, enumerating a <code><a
   href="#storage2">Storage</a></code> object must enumerate through the
   currently stored and <span>accessible</span> keys in the list the object
   is associated with. (It must not enumerate the values or the actual
   members of the interface). In the ECMAScript DOM binding, <code><a
   href="#storage2">Storage</a></code> objects must support dereferencing
   such that getting a property that is not a member of the object (i.e. is
   neither a member of the <code><a href="#storage2">Storage</a></code>
   interface nor of <code title=dom-Object>Object</code>) must invoke the
   <code title=dom-Storage-getItem><a href="#getitem">getItem()</a></code>
   method with the property's name as the argument, and setting such a
   property must invoke the <code title=dom-Storage-setItem><a
   href="#setitem">setItem()</a></code> method with the property's name as
   the first argument and the given value as the second argument.

  <h4 id=the-storageitem><span class=secno>4.11.3. </span>The <code><a
   href="#storageitem">StorageItem</a></code> interface</h4>

  <p>Items in <code><a href="#storage2">Storage</a></code> objects are
   represented by objects implementing the <code><a
   href="#storageitem">StorageItem</a></code> interface.

  <pre class=idl>
interface <dfn id=storageitem>StorageItem</dfn> {
           attribute boolean <a href="#secure" title=dom-StorageItem-secure>secure</a>;
           attribute DOMString <a href="#value7" title=dom-StorageItem-value>value</a>;
};</pre>

  <p>In the ECMAScript DOM binding, <code><a
   href="#storageitem">StorageItem</a></code> objects must stringify to their
   <code title=dom-StorageItem-value><a href="#value7">value</a></code>
   attribute's value.

  <p>The <dfn id=value7 title=dom-StorageItem-value><code>value</code></dfn>
   attribute must return the current value of the key/value pair represented
   by the object. When the attribute is set, the user agent must invoke the
   <code title=dom-Storage-setItem><a href="#setitem">setItem()</a></code>
   method of the <code><a href="#storage2">Storage</a></code> object that the
   <code><a href="#storageitem">StorageItem</a></code> object is associated
   with, with the key that the <code><a
   href="#storageitem">StorageItem</a></code> object is associated with as
   the first argument, and the new given value of the attribute as the second
   argument.

  <p><code><a href="#storageitem">StorageItem</a></code> objects must be
   <em><a href="#live">live</a></em>, meaning that as the underlying <code><a
   href="#storage2">Storage</a></code> object has its key/value pairs
   updated, the <code><a href="#storageitem">StorageItem</a></code> objects
   must always return the actual value of the key/value pair they represent.

  <p>If the key/value pair has been deleted, the <code><a
   href="#storageitem">StorageItem</a></code> object must act as if its value
   was the empty string. On setting, the key/value pair will be recreated.

  <p>The <dfn id=secure
   title=dom-StorageItem-secure><code>secure</code></dfn> attribute must
   raise an <code>INVALID_ACCESS_ERR</code> exception when accessed or set
   from a script whose browsing context is not <span title="secure browsing
   context">considered secure</span><!--
  XXX xref -->. (Basically, if the
   page is not an SSL page.)

  <p>If the browsing context <em>is</em> secure, then the <code
   title=dom-StorageItem-secure><a href="#secure">secure</a></code> attribute
   must return true if the key/value pair is considered "safe only for secure
   content", and false if it is considered "safe for both secure and insecure
   content". If it is set to true, then the key/value pair must be flagged as
   "safe only for secure content". If it is set to false, then the key/value
   pair must be flagged as "safe for both secure and insecure content".

  <p>If a <code><a href="#storageitem">StorageItem</a></code> object is
   obtained by a script that is not running in a <span>secure browsing
   context</span>, and the item is then marked with the "safe only for secure
   content" flag by a script that <em>is</em> running in a secure context,
   the <code><a href="#storageitem">StorageItem</a></code> object must
   continue to be available to the first script, who will be able to read the
   value of the object. However, any attempt to <em>set</em> the value would
   then start raising exceptions as described in the previous section, and
   the key/value pair would no longer appear in the appropriate <code><a
   href="#storage2">Storage</a></code> object.

  <h4 id=the-sessionstorage><span class=secno>4.11.4. </span>The <code
   title=dom-sessionStorage><a
   href="#sessionstorage">sessionStorage</a></code> attribute</h4>

  <p>The <dfn id=sessionstorage
   title=dom-sessionStorage><code>sessionStorage</code></dfn> attribute
   represents the storage area specific to the current <a
   href="#top-level">top-level browsing context</a>.

  <p>Each <a href="#top-level">top-level browsing context</a> has a unique
   set of session storage areas, one for each domain.

  <p>User agents should not expire data from a browsing context's session
   storage areas, but may do so when the user requests that such data be
   deleted, or when the UA detects that it has limited storage space, or for
   security reasons. User agents should always avoid deleting data while a
   script that could access that data is running. When a top-level browsing
   context is destroyed (and therefore permanently inaccessible to the user)
   the data stored in its session storage areas can be discarded with it, as
   the API described in this specification provides no way for that data to
   ever be subsequently retrieved.

  <p class=note>The lifetime of a browsing context can be unrelated to the
   lifetime of the actual user agent process itself, as the user agent may
   support resuming sessions after a restart.

  <p>When a new <code><a href="#htmldocument">HTMLDocument</a></code> is
   created, the user agent must check to see if the document's <a
   href="#top-level">top-level browsing context</a> has allocated a session
   storage area for that <a href="#domain0">document's domain</a>. If it has
   not, a new storage area for that document's domain must be created.

  <p>The <code><a href="#storage2">Storage</a></code> object for the
   document's associated <code><a href="#window">Window</a></code> object's
   <code title=dom-sessionStorage><a
   href="#sessionstorage">sessionStorage</a></code> attribute must then be
   associated with the domain's session storage area.

  <p>When a new <a href="#top-level">top-level browsing context</a> is
   created by cloning an existing <a href="#browsing0">browsing context</a>,
   the new browsing context must start with the same session storage areas as
   the original, but the two sets must from that point on be considered
   separate, not affecting each other in any way.

  <p>When a new <a href="#top-level">top-level browsing context</a> is
   created by a script in an existing <a href="#browsing0">browsing
   context</a>, or by the user following a link in an existing browsing
   context, or in some other way related to a specific <code><a
   href="#htmldocument">HTMLDocument</a></code>, then, if the new context's
   first <code><a href="#htmldocument">HTMLDocument</a></code> has the same
   <a href="#domain0" title="document's domain">domain</a> as the <code><a
   href="#htmldocument">HTMLDocument</a></code> from which the new context
   was created, the new browsing context must start with a single session
   storage area. That storage area must be a copy of that domain's session
   storage area in the original browsing context, which from that point on
   must be considered separate, with the two storage areas not affecting each
   other in any way.</p>
  <!-- XXX define the case for window.open() -->

  <p id=sessionStorageEvent>When the <code title=dom-Storage-setItem><a
   href="#setitem">setItem()</a></code> method is called on a <code><a
   href="#storage2">Storage</a></code> object <var title="">x</var> that is
   associated with a session storage area, then, if the method does not raise
   a <a href="#security8">security exception</a>, in every <code><a
   href="#htmldocument">HTMLDocument</a></code> object whose <code><a
   href="#window">Window</a></code> object's <code
   title=dom-sessionStorage><a
   href="#sessionstorage">sessionStorage</a></code> attribute's <code><a
   href="#storage2">Storage</a></code> object is associated with the same
   storage area, other than <var title="">x</var>, a <code
   title=event-storage><a href="#storage3">storage</a></code> event must be
   fired, as <a href="#storage3" title=event-storage>described below</a>.

  <h4 id=the-globalstorage><span class=secno>4.11.5. </span>The <code
   title=dom-globalStorage><a href="#globalstorage">globalStorage</a></code>
   attribute</h4>

  <pre class=idl>interface <dfn id=storagelist>StorageList</dfn> {
  <a href="#storage2">Storage</a> <a href="#nameditem2" title=dom-Storagelist-namedItem>namedItem</a>(in DOMString domain);
};</pre>

  <p>The <dfn id=globalstorage
   title=dom-globalStorage><code>globalStorage</code></dfn> object provides a
   <code><a href="#storage2">Storage</a></code> object for each domain.

  <p>In the ECMAScript DOM binding, <code><a
   href="#storagelist">StorageList</a></code> objects must support
   dereferencing such that getting a property that is not a member of the
   object (i.e. is neither a member of the <code><a
   href="#storagelist">StorageList</a></code> interface nor of <code
   title=dom-Object>Object</code>) must invoke the <code
   title=dom-Storagelist-namedItem><a
   href="#nameditem2">namedItem()</a></code> method with the property's name
   as the argument.

  <p>User agents must have a set of global storage areas, one for each
   domain.

  <p>User agents should only expire data from the global storage areas for
   security reasons or when requested to do so by the user. User agents
   should always avoid deleting data while a script that could access that
   data is running. Data stored in global storage areas should be considered
   potentially user-critical. It is expected that Web applications will use
   the global storage areas for storing user-written documents.

  <p>The <dfn id=nameditem2
   title=dom-Storagelist-namedItem><code>namedItem(<var
   title="">domain</var>)</code></dfn> method tries to returns a <code><a
   href="#storage2">Storage</a></code> object associated with the given
   domain, according to the rules that follow.

  <div id=splitDomain>
   <p>The <var title="">domain</var> must first be split into an array of
    strings, by splitting the string at "." characters (U+002E FULL STOP). If
    the <var title="">domain</var> argument is the empty string, then the
    array is empty as well. If the <var title="">domain</var> argument is not
    empty but has no dots, then the array has one item, which is equal to the
    <var title="">domain</var> argument. If the <var title="">domain</var>
    argument contains consecutive dots, there will be empty strings in the
    array (e.g. the string "hello..world" becomes split into the three
    strings "hello", "", and "world", with the middle one being the empty
    string).</p>

   <p>Each component of the array must then have the IDNA ToASCII algorithm
    applied to it, with both the AllowUnassigned and UseSTD3ASCIIRules flags
    set. <a href="#refsRFC3490">[RFC3490]</a> If ToASCII fails to convert one
    of the components of the string, e.g. because it is too long or because
    it contains invalid characters, then the user agent must raise a
    <code>SYNTAX_ERR</code> exception. <a href="#refsDOM3CORE">[DOM3CORE]</a>
    The components after this step consist of only US-ASCII characters.</p>

   <p>The components of the array must then be converted to lowercase. Since
    only US-ASCII is involved at this step, this only requires converting
    characters in the range A-Z to the corresponding characters in the range
    a-z.</p>
  </div>

  <p>The resulting array is used in a comparison with another array, as
   described below. In addition, its components are concatenated together,
   each part separated by a dot (U+002E), to form the <dfn
   id=normalised0>normalised requested domain</dfn>.

  <p class=example>If the original <var title="">domain</var> was
   "&Aring;sg&aring;rd.Example.Com", then the resulting array would have the
   three items "xn--sgrd-poac", "example", and "com", and the normalised
   requested domain would be "xn--sgrd-poac.example.com".

  <p>Next, the domain part of the tuple forming the calling script's <a
   href="#origin0">origin</a> is processed to find if it is allowed to access
   the requested domain.

  <p>If the script's origin has no domain part, e.g. if only the server's IP
   address is known, and the <a href="#normalised0">normalised requested
   domain</a> is not the empty string, then the user agent must raise a <a
   href="#security8">security exception</a>.

  <p class=note>If the <a href="#normalised0">normalised requested domain</a>
   is the empty string, then the rest of this algorithm can be skipped. This
   is because in that situation, the comparison of the two arrays below will
   always find them to be the same &mdash; the first array in such a
   situation is also empty and so permission to access that storage area will
   always be given.

  <p>If the domain part of the script's origin contains no dots (U+002E) then
   the string "<code>.localdomain</code>" must be appended to the script's
   domain.

  <p>Then, the domain part of the script's origin must be turned into an
   array, being split, converted to ASCII, and lowercased as described for
   the <var title="">domain</var> argument <a href="#splitDomain">above</a>.

  <p>Of the two arrays, the longest one must then be shortened to the length
   of the shorter one, by dropping items from the start of the array.

  <div class=example>
   <p>If the <var title="">domain</var> argument is "www.example.com" and the
    script origin's domain part is "example.com" then the first array will be
    a three item array ("www", "example", "com"), and the second will be a
    two item array ("example", "com"). The first array is therefore
    shortened, dropping the leading parts, making both into the same array
    ("example", "com").</p>
  </div>

  <p>If the two arrays are not component-for-component identical in literal
   string comparisons, then the user agent must then raise a <a
   href="#security8">security exception</a>.

  <p>Otherwise, the user agent must check to see if it has allocated global
   storage area for the <a href="#normalised0">normalised requested
   domain</a>. If it has not, a new storage area for that domain must be
   created.

  <p>The user agent must then create a <code><a
   href="#storage2">Storage</a></code> object associated with that domain's
   global storage area, and return it.

  <p>When the requested <var title="">domain</var> is a top level domain, or
   the empty string, or a country-specific sub-domain like "co.uk" or
   "ca.us", the associated global storage area is known as <dfn
   id=public0>public storage area</dfn>

  <div id=globalStorageEvent>
   <p>The <code title=dom-Storage-setItem><a
    href="#setitem">setItem()</a></code> method might be called on a <code><a
    href="#storage2">Storage</a></code> object that is associated with a
    global storage area for a domain <var title="">d</var>, created by a
    <code><a href="#storagelist">StorageList</a></code> object associated
    with a <code><a href="#window">Window</a></code> object <var
    title="">x</var>. Whenever this occurs, if the method didn't raise an
    exception, a <code title=event-storage><a
    href="#storage3">storage</a></code> event must be fired, as described
    below, in every <code><a href="#htmldocument">HTMLDocument</a></code>
    object that matches the following conditions:</p>

   <ul>
    <li>Its <code><a href="#window">Window</a></code> object is not <var
     title="">x</var>, and

    <li>Its <code><a href="#window">Window</a></code> object's <code
     title=dom-sessionStorage><a
     href="#sessionstorage">globalStorage</a></code> attribute's <code><a
     href="#storagelist">StorageList</a></code> object's <code
     title=dom-Storagelist-namedItem><a
     href="#nameditem2">namedItem()</a></code> method would not raise a <a
     href="#security8">security exception</a> according to the rules above if
     it was invoked with the domain <var title="">d</var>.
   </ul>

   <p>In other words, every other document that has access to that domain's
    global storage area is notified of the change.</p>
  </div>

  <h4 id=the-storage0><span class=secno>4.11.6. </span>The <code
   title=event-storage><a href="#storage3">storage</a></code> event</h4>

  <p>The <dfn id=storage3 title=event-storage><code>storage</code></dfn>
   event is fired in an <code><a href="#htmldocument">HTMLDocument</a></code>
   when a storage area changes, as described in the previous two sections (<a
   href="#sessionStorageEvent">for session storage</a>, <a
   href="#globalStorageEvent">for global storage</a>).

  <p>When this happens, a <code><a href="#storage2">storage</a></code> event
   in no namespace, which bubbles, is not cancelable, has no default action,
   and which uses the <code><a href="#storageevent">StorageEvent</a></code>
   interface described below, must be fired on <a href="#the-body0">the body
   element</a>.

  <p>However, it is possible (indeed, for session storage areas, likely) that
   the target <code><a href="#htmldocument">HTMLDocument</a></code> object is
   not active at that time. For example, it might not be the <a
   href="#current0">current entry</a> in the session history; user agents
   typically stop scripts from running in pages that are in the history. In
   such cases, the user agent must instead delay the firing of the event
   until such time as the <code><a
   href="#htmldocument">HTMLDocument</a></code> object in question becomes
   active again.

  <p>When there are multiple delayed <code><a
   href="#storage2">storage</a></code> events for the same <code><a
   href="#htmldocument">HTMLDocument</a></code> object, user agents should
   coalesce events with the same <code title=dom-Storageevent-domain><a
   href="#domain1">domain</a></code> value (dropping duplicates).

  <p>If the DOM of a page that has delayed <code><a
   href="#storage2">storage</a></code> events queued up is <a href="#discard"
   title=discard>discarded</a>, then the delayed events are dropped as well.

  <pre class=idl>interface <dfn id=storageevent>StorageEvent</dfn> : Event {
  readonly attribute DOMString <a href="#domain1" title=dom-StorageEvent-domain>domain</a>;
  void <a href="#initstorageevent" title=dom-StorageEvent-initStorageEvent>initStorageEvent</a>(in DOMString typeArg, in boolean canBubbleArg, in boolean cancelableArg, in DOMString domainArg);
  void <a href="#initstorageeventns" title=dom-StorageEvent-initStorageEventNS>initStorageEventNS</a>(in DOMString namespaceURIArg, in DOMString typeArg, in boolean canBubbleArg, in boolean cancelableArg, in DOMString domainArg);
};</pre>

  <p>The <dfn id=initstorageevent
   title=dom-StorageEvent-initStorageEvent><code>initStorageEvent()</code></dfn>
   and <dfn id=initstorageeventns
   title=dom-StorageEvent-initStorageEventNS><code>initStorageEventNS()</code></dfn>
   methods must initialise the event in a manner analogous to the
   similarly-named methods in the DOM3 Events interfaces. <a
   href="#refsDOM3EVENTS">[DOM3EVENTS]</a>

  <p>The <dfn id=domain1
   title=dom-StorageEvent-domain><code>domain</code></dfn> attribute of the
   <code><a href="#storageevent">StorageEvent</a></code> event object must be
   set to the name of the domain associated with the storage area that
   changed if that storage area is a global storage area, or the string
   "<code>#session</code>" if it was a session storage area.</p>
  <!-- XXX onstorage should be defined -->

  <h4 id=miscellaneous0><span class=secno>4.11.7. </span>Miscellaneous
   implementation requirements for storage areas</h4>

  <h5 id=disk-space><span class=secno>4.11.7.1. </span>Disk space</h5>

  <p>User agents should limit the total amount of space allowed for a domain
   based on the domain of the page setting the value.

  <p>User agents should not limit the total amount of space allowed on a
   per-storage-area basis, otherwise a site could just store data in any
   number of subdomains, e.g. storing up to the limit in a1.example.com,
   a2.example.com, a3.example.com, etc, circumventing per-domain limits.

  <p>User agents should consider additional quota mechanisms (for example
   limiting the amount of space provided to a domain's subdomains as a group)
   so that hostile authors can't run scripts from multiple subdomains all
   adding data to the global storage area in an attempted denial-of-service
   attack.

  <p>User agents may prompt the user when per-domain space quotas are
   reached, allowing the user to grant a site more space. This enables sites
   to store many user-created documents on the user's computer, for instance.

  <p>User agents should allow users to see how much space each domain is
   using.

  <p>If the storage area space limit is reached during a <code
   title=dom-Storage-setItem><a href="#setitem">setItem()</a></code> call,
   the user agent should raise an exception.</p>
  <!-- XXX which one? -->

  <p>A mostly arbitrary limit of five megabytes per domain is recommended.
   Implementation feedback is welcome and will be used to update this
   suggestion in future.

  <h5 id=threads0><span class=secno>4.11.7.2. </span>Threads</h5>

  <p>Multiple browsing contexts must be able to access the global storage
   areas simultaneously in a predictable manner. Scripts must not be able to
   detect any concurrent script execution.

  <p>This is required to guarentee that the <code title=dom-Storage-length><a
   href="#length7">length</a></code> attribute of a <code><a
   href="#storage2">Storage</a></code> object never changes while a script is
   executing, other than in a way that is predictable by the script itself.

  <p>There are various ways of implementing this requirement. One is that if
   a script running in one browsing context accesses a global storage area,
   the UA blocks scripts in other browsing contexts when they try to access
   <em>any</em> global storage area until the first script has executed to
   completion. (Similarly, when a script in one browsing context accesses its
   session storage area, any scripts that have the same top level browsing
   context and the same domain would block when accessing their session
   storage area until the first script has executed to completion.) Another
   (potentially more efficient but probably more complex) implementation
   strategy is to use optimistic transactional script execution. This
   specification does not require any particular implementation strategy, so
   long as the requirement above is met.

  <h4 id=security5><span class=secno>4.11.8. </span>Security and privacy</h4>

  <h5 id=user-tracking><span class=secno>4.11.8.1. </span>User tracking</h5>

  <p>A third-party advertiser (or any entity capable of getting content
   distributed to multiple sites) could use a unique identifier stored in its
   domain's global storage area to track a user across multiple sessions,
   building a profile of the user's interests to allow for highly targeted
   advertising. In conjunction with a site that is aware of the user's real
   identity (for example an e-commerce site that requires authenticated
   credentials), this could allow oppressive groups to target individuals
   with greater accuracy than in a world with purely anonymous Web usage.

  <p>The <code title=dom-globalStorage><a
   href="#globalstorage">globalStorage</a></code> object also introduces a
   way for sites to cooperate to track users over multiple domains, by
   storing identifying data in "<a href="#public0" title="public storage
   area">public</a>" top-level domain storage area, accessible by any domain.

  <p>There are a number of techniques that can be used to mitigate the risk
   of user tracking:

  <ul>
   <li>
    <p>Blocking third-party storage: user agents may restrict access to the
     <code title=dom-globalStorage><a
     href="#globalstorage">globalStorage</a></code> object to scripts
     originating at the domain of the top-level document of the <a
     href="#browsing0">browsing context</a>.</p>

    <p>This blocks a third-party site from using its private storage area for
     tracking a user, but top-level sites could still cooperate with third
     parties to perferm user tracking by using the "<a href="#public0"
     title="public storage area">public</a>" storage area.</p>

   <li>
    <p>Expiring stored data: user agents may automatically delete stored data
     after a period of time.</p>

    <p>For example, a user agent could treat the global storage area as
     session-only storage, deleting the data once the user had closed all the
     <span>browsing contexts</span> that could access it.</p>

    <p>This can restrict the ability of a site to track a user, as the site
     would then only be able to track the user across multiple sessions when
     he authenticates with the site itself (e.g. by making a purchase or
     logging in to a service).</p>
    <!-- XXX should there be an explicit way for sites to state when
    data should expire? as in
    globalStorage['example.com'].expireData(365); ? -->
    

   <li>
    <p>Blocking access to the top-level domain ("<a href="#public0"
     title="public storage area">public</a>") storage areas: user agents may
     prevent domains from storing data in and reading data from the top-level
     domain entries in the <code title=dom-globalStorage><a
     href="#globalstorage">globalStorage</a></code> object.</p>

    <p>In practice this requires a detailed list of all the "public"
     second-level (and third-level) domains. For example, content at the
     domain <code>www.example.com</code> would be allowed to access
     <code>example.com</code> data but not <code>com</code> data; content at
     the domain <code>example.co.uk</code> would be allowed access to
     <code>example.co.uk</code> but not <code>co.uk</code> or
     <code>uk</code>; and content at <code>example.chiyoda.tokyo.jp</code>
     would be allowed access to <code>example.chiyoda.tokyo.jp</code> but not
     <code>chiyoda.tokyo.jp</code>, <code>tokyo.jp</code>, or
     <code>jp</code>, while content at <code>example.metro.tokyo.jp</code>
     would be allowed access to both <code>example.metro.tokyo.jp</code> and
     <code>metro.tokyo.jp</code> but not <code>tokyo.jp</code> or
     <code>jp</code>. The problem is even more convoluted when one considers
     private domains with third-party subdomains such as
     <code>dyndns.org</code> or <code>uk.com</code>.</p>

    <p>Blocking access to the "<a href="#public0" title="public storage
     area">public</a>" storage areas can also prevent innocent sites from
     cooperating to provide services beneficial to the user.</p>

   <li>
    <p>Treating persistent storage as cookies: user agents may present the
     persistent storage feature to the user in a way that does not
     distinguish it from HTTP session cookies. <a
     href="#refsRFC2965">[RFC2965]</a></p>

    <p>This might encourage users to view persistent storage with healthy
     suspicion.</p>

   <li>
    <p>Site-specific white-listing of access to "<a href="#public0"
     title="public storage area">public</a>" storage area: user agents may
     allow sites to access persistent storage for their own domain and
     subdomains in an unrestricted manner, but require the user to authorise
     access to the storage area of higher-level domains.</p>

    <p>For example, code at <code>example.com</code> would be always allowed
     to read and write data for <code>www.example.com</code> and
     <code>example.com</code>, but if it tried to access <code>com</code>,
     the user agent could display a non-modal message informing the user that
     the page requested access to <code>com</code> and offering to allow it.</p>

   <li>
    <p>Origin-tracking of persistent storage data: user agents may record the
     domain of the script that caused data to be stored.</p>

    <p>If this information is then used to present the view of data currently
     in persistent storage, it would allow the user to make informed
     decisions about which parts of the persistent storage to prune. Combined
     with a blacklist ("delete this data and prevent this domain from ever
     storing data again"), the user can restrict the use of persistent
     storage to sites that he trusts.</p>

   <li>
    <p>Shared blacklists: user agents may allow users to share their
     persistent storage domain blacklists.</p>

    <p>This would allow communities to act together to protect their privacy.</p>
  </ul>

  <p>While these suggestions prevent trivial use of this API for user
   tracking, they do not block it altogether. Within a single domain, a site
   can continue to track the user across multiple sessions, and can then pass
   all this information to the third party along with any identifying
   information (names, credit card numbers, addresses) obtained by the site.
   If a third party cooperates with multiple sites to obtain such
   information, a profile can still be created.

  <p>However, user tracking is to some extent possible even with no
   cooperation from the user agent whatsoever, for instance by using session
   identifiers in URIs, a technique already commonly used for innocuous
   purposes but easily repurposed for user tracking (even retroactively).
   This information can then be shared with other sites, using using
   visitors' IP addresses and other user-specific data (e.g. user-agent
   headers and configuration settings) to combine separate sessions into
   coherent user profiles.

  <h5 id=cookie><span class=secno>4.11.8.2. </span>Cookie resurrection</h5>

  <p>If the user interface for persistent storage presents data in the
   persistent storage feature separately from data in HTTP session cookies,
   then users are likely to delete data in one and not the other. This would
   allow sites to use the two features as redundant backup for each other,
   defeating a user's attempts to protect his privacy.

  <h5 id=integrity><span class=secno>4.11.8.3. </span>Integrity of "public"
   storage areas</h5>

  <p>Since the "<a href="#public0" title="public storage area">public</a>"
   global storage areas are accessible by content from many different
   parties, it is possible for third-party sites to delete or change
   information stored in those areas in ways that the originating sites may
   not expect.

  <p>Authors must not use the "<a href="#public0" title="public storage
   area">public</a>" global storage areas for storing sensitive data. Authors
   must not trust information stored in "<a href="#public0" title="public
   storage area">public</a>" global storage areas.

  <h5 id=cross-protocol><span class=secno>4.11.8.4. </span>Cross-protocol and
   cross-port attacks</h5>

  <p>This API makes no distinction between content served over HTTP, FTP, or
   other host-based protocols, and does not distinguish between content
   served from different ports at the same host.

  <p>Thus, for example, data stored in the global persistent storage for
   domain "www.example.com" by a page served from HTTP port 80 will be
   available to a page served in <code>http://example.com:18080/</code>, even
   if the latter is an experimental server under the control of a different
   user.

  <p>Since the data is not sent over the wire by the user agent, this is not
   a security risk in its own right. However, authors must take proper steps
   to ensure that all hosts that have fully qualified host names that are
   subsets of hosts dealing with sensitive information are as secure as the
   originating hosts themselves.

  <p>Similarly, authors must ensure that all Web servers on a host,
   regardless of the port, are equally trusted if any of them are to use
   persistent storage. For instance, if a Web server runs a production
   service that makes use of the persistent storage feature, then other users
   that have access to that machine and that can run a Web server on another
   port will be able to access the persistent storage added by the production
   service (assuming they can trick a user into visiting their page).

  <p>However, if one is able to trick users into visiting a Web server with
   the same host name but on a different port as a production service used by
   these users, then one could just as easily fake the look of the site and
   thus trick users into authenticating with the fake site directly,
   forwarding the request to the real site and stealing the credentials in
   the process. Thus, the persistent storage feature is considered to only
   minimally increase the risk involved.

  <p class=big-issue>What about if someone is able to get a server up on a
   port, and can then send people to that URI? They could steal all the data
   with no further interaction. How about putting the port number at the end
   of the string being compared? (Implicitly.)

  <h5 id=dns-spoofing><span class=secno>4.11.8.5. </span>DNS spoofing attacks</h5>

  <p>Because of the potential for DNS spoofing attacks, one cannot guarentee
   that a host claiming to be in a certain domain really is from that domain.
   The <code title=dom-StorageItem-secure><a href="#secure">secure</a></code>
   attribute is provided to mark certain key/value pairs as only being
   accessible to pages that have been authenticated using secure certificates
   (or similar mechanisms).

  <p>Authors must ensure that they do not mark sensitive items as "safe for
   both secure and insecure content". (To prevent the risk of a race
   condition, data stored by scripts in secure contexts default to being
   marked as "safe only for secure content".)

  <h5 id=cross-directory><span class=secno>4.11.8.6. </span>Cross-directory
   attacks</h5>

  <p>Different authors sharing one host name, for example users hosting
   content on <code>geocities.com</code>, all share one persistent storage
   object. There is no feature to restrict the access by pathname. Authors on
   shared hosts are therefore recommended to avoid using the persistent
   storage feature, as it would be trivial for other authors to read from and
   write to the same storage area.

  <p class=note>Even if a path-restriction feature was made available, the
   usual DOM scripting security model would make it trivial to bypass this
   protection and access the data from any path.

  <h5 id=public><span class=secno>4.11.8.7. </span>Public storage areas
   corresponding to hosts</h5>

  <p>If a "<a href="#public0" title="public storage area">public</a>" global
   storage area corresponds to a host, as it typically does if for private
   domains with third-party subdomains such as dyndns.org or uk.com, the host
   corresponding to the "public" domain has access to all the storage areas
   of its third-party subdomains. In general, authors are discouraged from
   using the <code title=dom-globalStorage><a
   href="#globalstorage">globalStorage</a></code> API for sensitive data
   unless the operators of all the domains involved are trusted.

  <p>User agents may mitigate this problem by preventing hosts corresponding
   to "<a href="#public0" title="public storage area">public</a>" global
   storage areas from accessing any storage areas other than their own.

  <h5 id=storage0><span class=secno>4.11.8.8. </span>Storage areas in the
   face of untrusted higher-level domains that do not correspond to public
   storage areas</h5>

  <p>Authors should not store sensitive data using the global storage APIs if
   there are hosts with fully-qualified domain names that are subsets of
   their own which they do not trust. For example, an author at
   <code>finance.members.example.net</code> should not store sensitive
   financial user data in the <code>finance.members.example.net</code>
   storage area if he does not trust the host that runs
   <code>example.net</code>.

  <h5 id=storage1><span class=secno>4.11.8.9. </span>Storage areas in the
   face of untrusted subdomains</h5>

  <p>If an author publishing content on one host, e.g.
   <code>example.com</code>, wishes to use the <code
   title=dom-globalStorage><a href="#globalstorage">globalStorage</a></code>
   API but does not wish any content on the host's subdomains to access the
   data, the author should use an otherwise non-existent subdomain name,
   e.g., <code>private.example.com</code>, to store the data. This will be
   accessible only to that host (and its parent domains), and not to any of
   the real subdomains (e.g. <code>upload.example.com</code>).

  <h5 id=implementation><span class=secno>4.11.8.10. </span>Implementation
   risks</h5>

  <p>The two primary risks when implementing this persistent storage feature
   are letting hostile sites read information from other domains, and letting
   hostile sites write information that is then read from other domains.

  <p>Letting third-party sites read data that is not supposed to be read from
   their domain causes <em>information leakage</em>, For example, a user's
   shopping wishlist on one domain could be used by another domain for
   targeted advertising; or a user's work-in-progress confidential documents
   stored by a word-processing site could be examined by the site of a
   competing company.

  <p>Letting third-party sites write data to the storage areas of other
   domains can result in <em>information spoofing</em>, which is equally
   dangerous. For example, a hostile site could add items to a user's
   wishlist; or a hostile site could set a user's session identifier to a
   known ID that the hostile site can then use to track the user's actions on
   the victim site.

  <p>A risk is also presented by servers on local domains having host names
   matching top-level domain names, for instance having a host called "com"
   or "net". Such hosts might, if implementations fail to correctly implement
   the <code>.localdomain</code> suffixing, <!-- XXX cross ref --> have full
   access to all the data stored in a UA's persistent storage for that top
   level domain.

  <p>Thus, strictly following the model described in this specification is
   important for user security.

  <p>In addition, a number of optional restrictions related to the "<a
   href="#public0" title="public storage area">public</a>" global storage
   areas are suggested in the previous sections. The design of this API is
   intended to be such that not supporting these restrictions, or supporting
   them less than perfectly, does not result in critical security problems.
   However, implementations are still encouraged to create and maintain a
   list of "<a href="#public0" title="public storage area">public</a>"
   domains, and apply the restrictions described above.

  <h3 id=sql><span class=secno>4.12. </span>Client-side database storage</h3>

  <h4 id=introduction1><span class=secno>4.12.1. </span>Introduction</h4>

  <p class=big-issue>...

  <h4 id=executing><span class=secno>4.12.2. </span>Executing SQL statements</h4>

  <p>Each <a href="#origin0">origin</a> must have an associated database
   unique to that origin. An author can interact with the database using the
   <code title=dom-executeSql><a href="#executesql">executeSql()</a></code>
   method.

  <p>When the <dfn id=executesql title=dom-executeSql><code>executeSql(<var
   title="">sqlStatement</var>, <var
   title="">arguments...</var>)</code></dfn> method is invoked, the user
   agent must first interpret the first argument to the method (<var
   title="">sqlStatement</var>) as an SQL statement, replacing any <code
   title="">?</code> placeholders in the statement with the values given in
   the subsequent arguments (<var title="">arguments...</var>), and must then
   evaluate the statement as an SQL statement in the context of the database
   associated with the <a href="#origin0">origin</a> of the <a
   href="#active">active document</a> of the <a href="#browsing0">browsing
   context</a> of the <code><a href="#window">Window</a></code> object on
   which the method was called. <a href="#refsSQL">[SQL]</a>

  <p>If the <code title=dom-executeSql><a
   href="#executesql">executeSql()</a></code> method is called with a
   different number of arguments after the statement than there are
   placeholder <code title="">?</code> characters in the statement, then the
   method must raise a <code>SYNTAX_ERR</code> exception.

  <p>Otherwise, the method must return a <code><a
   href="#resultset">ResultSet</a></code> object representing the result of
   the operation.

  <p>The user agent must act as if the database was hosted in an otherwise
   completely empty environment with no resources. For example, attempts to
   read from or write to the filesystem will fail.

  <p>User agents should limit the total amount of space allowed for each
   origin, but may prompt the user and extend the limit if a database is
   reaching its quota. User agents should allow users to see how much space
   each database is using.

  <p>A mostly arbitrary limit of five megabytes per origin is recommended.
   Implementation feedback is welcome and will be used to update this
   suggestion in future.

  <p>SQL inherently supports multiple concurrent connections. Authors should
   make use of SQL's transaction features if multiple scripts are expected to
   interact with the same database simultaneously (as could happen if the
   same page was opened in two different <a href="#browsing0" title="browsing
   context">browsing contexts</a>).

  <p class=note>A future version of this specification may define the exact
   SQL subset required in more detail.

  <h4 id=database><span class=secno>4.12.3. </span>Database query results</h4>

  <p>Calls to the <code title=dom-executeSql><a
   href="#executesql">executeSql()</a></code> method return <code><a
   href="#resultset">ResultSet</a></code> objects.

  <pre class=idl>interface <dfn id=resultset>ResultSet</dfn> {
  // cursor
  readonly attribute boolean <a href="#validrow" title=dom-ResultSet-validRow>validRow</a>;
  void <a href="#next0" title=dom-ResultSet-next>next</a>();

  // current row accessors
  readonly attribute unsigned int <a href="#length8" title=dom-ResultSet-length>length</a>;
  DOMString <a href="#getname" title=dom-ResultSet-getName>getName</a>(in unsigned int field);
  Object <a href="#itemfield" title=dom-ResultSet-item>item</a>(in unsigned int field);
  Object <a href="#nameditem3" title=dom-ResultSet-namedItem>namedItem</a>(in DOMString field);

  // general result accessors
  readonly attribute int <a href="#insertid" title=dom-ResultSet-insertId>insertId</a>;
};</pre>

  <p>A <code><a href="#resultset">ResultSet</a></code> object has a cursor
   which visits the results of a SQL statement, in the order returned.
   Initially, the cursor must point at the first row returned by the
   statement, if any. Once a row has been visited, it cannot be visited again
   (the cursor cannot go backwards).

  <p>The <dfn id=validrow
   title=dom-ResultSet-validRow><code>validRow</code></dfn> attribute must
   return return true if the <code><a href="#resultset">ResultSet</a></code>
   object's cursor is at a row with data. If the cursor has been moved beyond
   the last row of the results, or if there were no results for the SQL
   statement in question, then the method must return false.

  <p>The <dfn id=next0 title=dom-ResultSet-next><code>next()</code></dfn>
   method must advance the cursor to the next row. If there are no more rows
   it must advance the cursor past the end of the results, so that <code
   title=dom-ResultSet-validRow><a href="#validrow">validRow</a></code> will
   return false.

  <p>Each row of the results consists of a set of fields. Each field has a
   name and a value. The fields are ordered. The names of the fields, and
   their order, must be the same for every row in the results.

  <p>The <dfn id=length8 title=dom-ResultSet-length><code>length</code></dfn>
   attribute must return the number of fields in each row. If the <code><a
   href="#resultset">ResultSet</a></code> object has no results rows (i.e. if
   the SQL statement executed did not return any results) then the attribute
   must return zero.

  <p>The <dfn id=getname title=dom-ResultSet-getName><code>getName(<var
   title="">field</var>)</code></dfn> method must return the name of the
   field with index <var title="">field</var>.

  <p>The <dfn id=itemfield title=dom-ResultSet-item><code>item(<var
   title="">field</var>)</code></dfn> method must return the value of the
   field with index <var title="">field</var>. In the ECMAScript binding, the
   object's [[Get]] method, when invoked with a numeric argument, must have
   the same effect as calling the <code title=dom-ResultSet-item><a
   href="#itemfield">item()</a></code> method.

  <p>If the <var title="">field</var> argument of either the <code
   title=dom-ResultSet-getName><a href="#getname">getName()</a></code> or
   <code title=dom-ResultSet-item><a href="#itemfield">item()</a></code>
   methods is ever less than zero or greater than or equal to the number of
   fields in each row, or if those methods are called when the <code><a
   href="#resultset">ResultSet</a></code> object has no results rows, the
   methods must instead raise an <code>INDEX_SIZE_ERR</code> exception.

  <p>The <dfn id=nameditem3
   title=dom-ResultSet-namedItem><code>namedItem(<var
   title="">field</var>)</code></dfn> method must return the value of the
   field with the name <var title="">field</var>. If there is no field with
   that name, the method must instead raise a <code>SYNTAX_ERR</code>
   exception. In the ECMAScript binding, the object's [[Get]] method, when
   invoked with a non-numeric argument, must have the same effect as calling
   the <code title=dom-ResultSet-namedItem><a
   href="#nameditem3">namedItem()</a></code> method.

  <p>The <dfn id=insertid
   title=dom-ResultSet-insertId><code>insertId</code></dfn> attribute must
   return the row ID of the row that the <code><a
   href="#resultset">ResultSet</a></code> object's SQL statement inserted
   into the database, if the statement inserted a row. If the statement
   inserted multiple rows, the ID of the last row must be the one returned.
   If the statement did not insert a row, then the attribute must instead
   raise an <code>INVALID_ACCESS_ERR</code> exception.

  <h4 id=privacy><span class=secno>4.12.4. </span>Privacy</h4>

  <p>In contrast with the <code title=dom-globalStorage><a
   href="#globalstorage">globalStorage</a></code> feature, which
   intentionally allows data to be accessed across multiple domains,
   protocols, and ports (albeit in a controlled fashion), this database
   feature is limited to scripts running with the same <a
   href="#origin0">origin</a> as the database. Thus, it is expected that the
   privacy implications be equivalent to those already present in allowing
   scripts to communicate with their originating host.

  <p>User agents are encouraged to treat data stored in databases in the same
   way as cookies for the purposes of user interfaces, to reduce the risk of
   using this feature for cookie resurrection.

  <h4 id=security6><span class=secno>4.12.5. </span>Security</h4>

  <h5 id=user-agents><span class=secno>4.12.5.1. </span>User agents</h5>

  <p>User agent implementors are strongly encouraged to audit all their
   supported SQL statements for security implications. For example, <code
   title="">LOAD DATA INFILE</code> is likely to pose security risks and
   there is little reason to support it.

  <p>In general, it is recommended that user agents not support features that
   control how databases are stored on disk. For example, there is little
   reason to allow Web authors to control the character encoding used in the
   disk representation of the data, as all data in ECMAScript is implicitly
   UTF-16.

  <h5 id=sql-injection><span class=secno>4.12.5.2. </span>SQL injection</h5>

  <p>Authors are strongly recommended to make use of the <code
   title="">?</code> placeholder feature of the <code title=dom-executeSql><a
   href="#executesql">executeSql()</a></code> method, and to never construct
   SQL statements on the fly.

  <h2 id=editing><span class=secno>5. </span><dfn id=editing0>Editing</dfn></h2>

  <p>This section describes various features that allow authors to enable
   users to edit documents and parts of documents interactively.

  <h3 id=editing-intro><span class=secno>5.1. </span>Introduction</h3>

  <p><em>This section is non-normative.</em>

  <p class=big-issue>Would be nice to explain how these features work
   together.

  <h3 id=contenteditable><span class=secno>5.2. </span>The <code
   title=attr-contenteditable><a
   href="#contenteditable0">contenteditable</a></code> attribute</h3>

  <p>The <dfn id=contenteditable0
   title=attr-contenteditable><code>contenteditable</code></dfn> attribute is
   a common attribute. User agents must support this attribute on all <a
   href="#html-elements">HTML elements</a>.

  <p>The <code title=attr-contenteditable><a
   href="#contenteditable0">contenteditable</a></code> attribute is an <a
   href="#enumerated">enumerated attribute</a> whose keywords are the empty
   string, <code title="">true</code>, and <code title="">false</code>. The
   empty string and the <code title="">true</code> keyword map to the
   <em>true</em> state. The <code title="">false</code> keyword maps to the
   <em>false</em> state, which is also the <em>invalid value default</em>.
   There is no <em>missing value default</em>.

  <p>If an HTML element has a <code title=attr-contenteditable><a
   href="#contenteditable0">contenteditable</a></code> attribute set to the
   true state, or if its nearest ancestor with the <code
   title=attr-contenteditable><a
   href="#contenteditable0">contenteditable</a></code> attribute set has its
   attribute set to the true state, or if it has no ancestors with the <code
   title=attr-contenteditable><a
   href="#contenteditable0">contenteditable</a></code> attribute set but the
   <code>Document</code> has <code title=dom-document-designMode><a
   href="#designMode">designMode</a></code> enabled, then the UA must treat
   the element as <dfn id=editable0>editable</dfn> (as described below).

  <p>Otherwise, either the HTML element has a <code
   title=attr-contenteditable><a
   href="#contenteditable0">contenteditable</a></code> attribute set to the
   false state, or its nearest ancestor with the <code
   title=attr-contenteditable><a
   href="#contenteditable0">contenteditable</a></code> attribute set is not
   <em><a href="#editable0">editable</a></em>, or it has no ancestor with the
   <code title=attr-contenteditable><a
   href="#contenteditable0">contenteditable</a></code> attribute set and the
   <code>Document</code> itself has <code title=dom-document-designMode><a
   href="#designMode">designMode</a></code> disabled, and the element is thus
   not editable.

  <p>The <dfn id=contenteditable1
   title=dom-contentEditable><code>contentEditable</code></dfn> DOM
   attribute, on getting, must return the string "<code
   title="">inherit</code>" if the content attribute isn't set, "<code
   title="">true</code>" if the attribute is set and has the true state, and
   "<code title="">false</code>" otherwise. On setting, if the new value is
   case-insensitively<!-- XXX ascii --> equal to the string "<code
   title="">inherit</code>" then the content attribute must be removed, if
   the new value is case-insensitively<!-- XXX
  ascii --> equal to the
   string "<code title="">true</code> then the content attribute must be set
   to the string "<code title="">true</code>, if the new value is
   case-insensitively<!-- XXX
  ascii --> equal to the string "<code
   title="">false</code> then the content attribute must be set to the string
   "<code title="">false</code>, and otherwise the attribute setter must
   raise a <code>SYNTAX_ERR</code> exception.

  <p>If an element is <a href="#editable0">editable</a> and its parent
   element is not, or if an element is <a href="#editable0">editable</a> and
   it has no parent element, then the element is an <dfn id=editing1>editing
   host</dfn>. Editable elements can be nested. User agents must make editing
   hosts focusable (which typicially means they enter the <span
   title=tabindex>tab order</span>). An editing host can contain non-editable
   sections, these are handled as described below. An editing host can
   contain non-editable sections that contain further editing hosts.

  <p>When an editing host has focus, it must have a <dfn id=caret>caret
   position</dfn> that specifies where the current editing position is. It
   may also have a <a href="#a-selection" title="the
   selection">selection</a>.</p>
  <!--- XXX xref to later section -->

  <p class=note>How the caret and selection are represented depends entirely
   on the UA.</p>
  <!-- XXX rendering requirement: The current caret should affect the
  line-height (i.e. it acts at least like an empty inline element) -->
  <!-- XXX document.designMode attribute -->

  <h4 id=user-editing><span class=secno>5.2.1. </span>User editing actions</h4>

  <p>There are several actions that the user agent should allow the user to
   perform while the user is interacting with an editing host. How exactly
   each action is triggered is not defined for every action, but when it is
   not defined, suggested key bindings are provided to guide implementors.

  <dl>
   <dt>Move the caret

   <dd>
    <p>User agents must allow users to move the caret to any position within
     an editing host, even into nested editable elements. This could be
     triggered as the default action of <code
     title=event-keydown>keydown</code> events with various key identifiers
     and as the default action of <code
     title=event-mousedown>mouseydown</code> events.

   <dt>Change the selection

   <dd>
    <p>User agents must allow users to change <a href="#a-selection">the
     selection</a> within an editing host, even into nested editable
     elements. This could be triggered as the default action of <code
     title=event-keydown>keydown</code> events with various key identifiers
     and as the default action of <code
     title=event-mousedown>mouseydown</code> events.

   <dt id=contenteditable-insertText>Insert text

   <dd>
    <p>This action must be triggered as the default action of a <code
     title=event-textInput>textInput</code> event, and may be triggered by
     other commands as well. It must cause the user agent to insert the
     specified text (given by the event object's <code title="">data</code>
     attribute in the case of the <code
     title=event-textInput>textInput</code> event) at the caret.</p>

    <p>If the caret is positioned somewhere where <a
     href="#inline-level0">inline-level content</a> is not allowed (e.g.
     because the element accepts "both block-level and inline-level content
     but not both", and the element already contains block-level content),
     then the user agent must not insert the text directly at the caret
     position. In such cases the behaviour is UA-dependent, but user agents
     must not, in response to a request to insert text, generate a DOM that
     is less conformant than the DOM prior to the request.</p>

    <p>User agents should allow users to insert new paragraphs into elements
     that only contain block-level content.</p>

    <div class=example>
     <p>For example, given the markup:</p>

     <pre>&lt;section&gt;
 &lt;dl&gt;
  &lt;dt&gt; Ben &lt;/dt&gt;
  &lt;dd&gt; Goat &lt;/dd&gt;
 &lt;/dl&gt;
&lt;/section&gt;</pre>

     <p>...the user agent should allow the user to insert <code><a
      href="#p">p</a></code> elements before and after the <code><a
      href="#dl">dl</a></code> element, as children of the <code><a
      href="#section">section</a></code> element.</p>
    </div>

   <dt id=contenteditable-breakBlock>Break block

   <dd>
    <p>UAs should offer a way for the user to request that the current block
     be broken at the caret, e.g. as the default action of a <code
     title=event-keydown>keydown</code> event whose identifier is the "Enter"
     key and that has no modifiers set.</p>

    <p>The exact behaviour is UA-dependent, but user agents must not, in
     response to a request to break a block, generate a DOM that is less
     conformant than the DOM prior to the request.

   <dt id=contenteditable-br>Insert a line separator

   <dd>
    <p>UAs should offer a way for the user to request an explicit line break
     at the caret position without breaking the block, e.g. as the default
     action of a <code title=event-keydown>keydown</code> event whose
     identifier is the "Enter" key and that has a shift modifier set. Line
     separators are typically found within a poem verse or an address. To
     insert a line break, the user agent must insert a <code><a
     href="#br">br</a></code> element.</p>

    <p>If the caret is positioned somewhere where <a
     href="#inline-level0">inline-level content</a> is not allowed (e.g.
     because the element accepts "both block-level and inline-level content
     but not both", and the element already contains block-level content),
     then the user agent must not insert the <code><a
     href="#br">br</a></code> element directly at the caret position. In such
     cases the behaviour is UA-dependent, but user agents must not, in
     response to a request to insert a line separator, generate a DOM that is
     less conformant than the DOM prior to the request.

   <dt id=contenteditable-delete>Delete

   <dd>
    <p>UAs should offer a way for the user to delete text and elements, e.g.
     as the default action of <code title=event-keydown>keydown</code> events
     whose identifiers are "U+0008" or "U+007F".</p>

    <p>Five edge cases in particular need to be considered carefully when
     implementing this feature: backspacing at the start of an element,
     backspacing when the caret is immediately after an element,
     forward-deleting at the end of an element, forward-deleting when the
     caret is immediately before an element, and deleting a <a
     href="#a-selection" title="the selection">selection</a> whose start and
     end points do not share a common parent node.</p>

    <p>In any case, the exact behaviour is UA-dependent, but user agents must
     not, in response to a request to delete text or an element, generate a
     DOM that is less conformant than the DOM prior to the request.

   <dt id=contenteditable-wrapSemantic>Insert, and wrap text in, semantic
    elements

   <dd>
    <p>UAs should offer a way for the user to mark text as having <a
     href="#em" title=em>stress emphasis</a> and as being <a href="#strong"
     title=strong>important</a>, and may offer the user the ability to mark
     text and blocks with other semantics.</p>

    <p>UAs should similarly offer a way for the user to insert empty semantic
     elements (such as, again, <code><a href="#em">em</a></code>, <code><a
     href="#strong">strong</a></code>, and others) to subsequently fill by
     entering text manually.</p>

    <p>UAs should also offer a way to remove those semantics from marked up
     text, and to remove empty semantic element that have been inserted.</p>

    <p>The exact behaviour is UA-dependent, but user agents must not, in
     response to a request to wrap semantics around some text or to insert or
     remove a semantic element, generate a DOM that is less conformant than
     the DOM prior to the request.

   <dt>Select and move non-editable elements nested inside editing hosts

   <dd>
    <p>UAs should offer a way for the user to move images and other
     non-editable parts around the content within an editing host. This may
     be done using the <a href="#drag-and">drag and drop</a> mechanism. User
     agents must not, in response to a request to move non-editable elements
     nested inside editing hosts, generate a DOM that is less conformant than
     the DOM prior to the request.

   <dt>Edit form controls nested inside editing hosts

   <dd>
    <p>When an <a href="#editable0">editable</a> form control is edited, the
     changes must be reflected in both its current value <em>and</em> its
     default value. For <code>input</code> elements this means updating the
     <code title=dom-input-defaultValue>defaultValue</code> DOM attribute as
     well as the <code title=dom-input-value>value</code> DOM attribute; for
     <code>select</code> elements it means updating the <code>option</code>
     elements' <code title=dom-option-defaultSelected>defaultSelected</code>
     DOM attribute as well as the <code
     title=dom-option-selected>selected</code> DOM attribute; for
     <code>textarea</code> elements this means updating the <code
     title=dom-textarea-defaultValue>defaultValue</code> DOM attribute as
     well as the <code title=dom-textarea-value>value</code> DOM attribute.
     (Updating the <code title="">default*</code> DOM attributes causes
     content attributes to be updated as well.)
   </dd>
   <!-- XXX something about not supporting resizing? -->
  </dl>
  <!-- XXX each action performed should be added to the undo history -->

  <p>User agents may perform several commands per user request; for example
   if the user selects a block of text and hits <kbd><kbd>Enter</kbd></kbd>,
   the UA might interpret that as a request to delete the content of <a
   href="#a-selection">the selection</a> followed by a request to break the
   block at that position.

  <h4 id=making><span class=secno>5.2.2. </span>Making entire documents
   editable</h4>

  <p>Documents have a <dfn id=designMode
   title=dom-document-designMode><code>designMode</code></dfn>, which can be
   either enabled or disabled.

  <p>The <code title=dom-document-designMode><a
   href="#designMode">designMode</a></code> DOM attribute on the
   <code>Document</code> object takes takes two values, "<code
   title="">on</code>" and "<code title="">off</code>". When it is set, the
   new value must be case-insensitively <!-- XXX ASCII case-folding -->
   compared to these two values. If it matches the "<code title="">on</code>"
   value, then <code title=dom-document-designMode><a
   href="#designMode">designMode</a></code> must be enabled, and if it
   matches the "<code title="">off</code>" value, then <code
   title=dom-document-designMode><a href="#designMode">designMode</a></code>
   must be disabled. Other values must be ignored.

  <p>When <code title=dom-document-designMode><a
   href="#designMode">designMode</a></code> is enabled, the DOM attribute
   must return the value "<code title="">on</code>", and when it is disabled,
   it must return the value "<code title="">off</code>".

  <p>The last state set must persist until the document is destroyed or the
   state is changed. Initially, documents must have their <code
   title=dom-document-designMode><a href="#designMode">designMode</a></code>
   disabled.

  <p>Enabling <code title=dom-document-designMode><a
   href="#designMode">designMode</a></code> causes scripts in general to be
   disabled and the document to become editable.

  <p>When the <code>Document</code> has <code
   title=dom-document-designMode><a href="#designMode">designMode</a></code>
   enabled, event listeners registered on the document or any elements owned
   by the document must do nothing.

  <h3 id=dnd><span class=secno>5.3. </span><dfn id=drag-and>Drag and
   drop</dfn></h3>
  <!--XXX

http://msdn.microsoft.com/workshop/author/datatransfer/overview.asp
http://msdn.microsoft.com/workshop/author/dhtml/reference/objects/clipboarddata.asp

> To implement this with simple interface I've proposed, events should be
> handled either by existing elements (like list items that compare their size
> and position of dragged element to decide whether element should be dropped
> before or after) or handled by container that would probably need to calculate
> positions of it's children and create new element to show drop target. Smooth
> Mac-like drag'n'drop can be implemented by animating drop target's
> padding/margin. So that's quite a bit of code that's going to be reinvented
> each time someone implements reordering.

<hyatt> :droptarget
<hyatt> or something
<hyatt> we don't support a pseudo-class for the drop target but that's a great idea
<Hixie_> yeah, thinking about that too
<Hixie_> :drop-target, :drop-target(above), :drop-target(below) and having ondragover be able to say "not on me, but next to me maybe"

http://msdn.microsoft.com/workshop/author/dhtml/reference/events/ondragstart.asp
http://msdn.microsoft.com/workshop/author/dhtml/reference/events/ondrag.asp
http://msdn.microsoft.com/workshop/author/dhtml/reference/events/ondragend.asp
http://msdn.microsoft.com/workshop/author/dhtml/reference/objects/obj_datatransfer.asp
http://developer.apple.com/documentation/AppleApplications/Conceptual/SafariJSProgTopics/Tasks/DragAndDrop.html
-->

  <p>This section defines an event-based drag-and-drop mechanism.

  <p>This specification does not define exactly what a <em>drag-and-drop
   operation</em> actually is.

  <p>On a visual medium with a pointing device, a drag operation could be the
   default action of a <code title=event-mousedown>mousedown</code> event
   that is followed by a series of <code
   title=event-mousemove>mousemove</code> events, and the drop could be
   triggered by the mouse being released.

  <p>On media without a pointing device, the user would probably have to
   explicitly indicate his intention to perform a drag-and-drop operation,
   stating what he wishes to drag and what he wishes to drop, respectively.

  <p>However it is implemented, drag-and-drop operations must have a starting
   point (e.g. where the mouse was clicked, or the start of <a
   href="#a-selection">the selection</a> or element that was selected for the
   drag), may have any number of intermediate steps (elements that the mouse
   moves over during a drag, or elements that the user picks as possible drop
   points as he cycles through possibilities), and must either have an end
   point (the element above which the mouse button was released, or the
   element that was finally selected), or be canceled. The end point must be
   the last element selected as a possible drop point before the drop occurs
   (so if the operation is not canceled, there must be at least one element
   in the middle step).

  <h4 id=the-dragevent><span class=secno>5.3.1. </span>The <code><a
   href="#dragevent">DragEvent</a></code> and <code><a
   href="#datatransfer0">DataTransfer</a></code> interfaces</h4>

  <p>The drag-and-drop processing model involves several events. They all use
   the <code><a href="#dragevent">DragEvent</a></code> interface.

  <pre class=idl>interface <dfn id=dragevent>DragEvent</dfn> : Event {
  readonly attribute <a href="#datatransfer0">DataTransfer</a> <a href="#datatransfer" title=dom-DragEvent-dataTransfer>dataTransfer</a>;
  void <a href="#initdragevent" title=dom-DragEvent-initDragEvent>initDragEvent</a>(in DOMString typeArg, in boolean canBubbleArg, in boolean cancelableArg);
  void <a href="#initdrageventns" title=dom-DragEvent-initDragEventNS>initDragEventNS</a>(in DOMString namespaceURIArg, in DOMString typeArg, in boolean canBubbleArg, in boolean cancelableArg);
};</pre>

  <p>The <dfn id=initdragevent
   title=dom-DragEvent-initDragEvent><code>initDragEvent()</code></dfn> and
   <dfn id=initdrageventns
   title=dom-DragEvent-initDragEventNS><code>initDragEventNS()</code></dfn>
   methods must initialise the event in a manner analogous to the
   similarly-named methods in the DOM3 Events interfaces. <a
   href="#refsDOM3EVENTS">[DOM3EVENTS]</a>

  <p>The <dfn id=datatransfer
   title=dom-DragEvent-dataTransfer><code>dataTransfer</code></dfn> attribute
   of the <code><a href="#dragevent">DragEvent</a></code> interface
   represents the context information for the event.

  <p>When a <code><a href="#dragevent">DragEvent</a></code> object is
   created, a new <code><a href="#datatransfer0">DataTransfer</a></code>
   object must be created and assigned to the <code
   title=dom-DragEvent-dataTransfer><a
   href="#datatransfer">dataTransfer</a></code> context information field of
   the event object.

  <pre class=idl>interface <dfn id=datatransfer0>DataTransfer</dfn> {
           attribute DOMString <a href="#dropeffect" title=dom-DataTransfer-dropEffect>dropEffect</a>;
           attribute DOMString <a href="#effectallowed" title=dom-DataTransfer-effectAllowed>effectAllowed</a>;
  void <a href="#cleardata" title=dom-DataTransfer-clearData>clearData</a>(in DOMString format);
  void <a href="#setdata" title=dom-DataTransfer-setData>setData</a>(in DOMString format, in DOMString data);
  DOMString <a href="#getdata" title=dom-DataTransfer-getData>getData</a>(in DOMString format);
  void <a href="#setdragimage" title=dom-DataTransfer-setDragImage>setDragImage</a>(in Element image, in long x, in long y);
  void <a href="#addelement" title=dom-DataTransfer-addElement>addElement</a>(in Element element);
};
</pre>

  <p><code><a href="#datatransfer0">DataTransfer</a></code> objects can
   conceptually contain various kinds of data.

  <p>When a <code><a href="#dragevent">DragEvent</a></code> event object is
   initialised, the <code><a href="#datatransfer0">DataTransfer</a></code>
   object created for the event's <code title=dom-DragEvent-dataTransfer><a
   href="#datatransfer">dataTransfer</a></code> member must be initialised as
   follows:

  <ul>
   <li>The <code><a href="#datatransfer0">DataTransfer</a></code> object must
    initially contain no data, no elements, and have no associated image.

   <li>The <code><a href="#datatransfer0">DataTransfer</a></code> object's
    <code title=dom-DataTransfer-effectAllowed><a
    href="#effectallowed">effectAllowed</a></code> attribute must be set to
    "<code title="">uninitialized</code>".

   <li>The <code title=dom-DataTransfer-dropEffect><a
    href="#dropeffect">dropEffect</a></code> attribute must be set to "<code
    title="">none</code>".
  </ul>

  <p>The <dfn id=dropeffect
   title=dom-DataTransfer-dropEffect><code>dropEffect</code></dfn> attribute
   controls the drag-and-drop feedback that the user is given during a
   drag-and-drop operation.

  <p>The attribute must ignore any attempts to set it to a value other than
   <code title="">none</code>, <code title="">copy</code>, <code
   title="">link</code>, and <code title="">move</code>. On getting, the
   attribute must return the last of those four values that it was set to.

  <p>The <dfn id=effectallowed
   title=dom-DataTransfer-effectAllowed><code>effectAllowed</code></dfn>
   attribute is used in the drag-and-drop processing model to initialise the
   <code title=dom-DataTransfer-dropEffect><a
   href="#dropeffect">dropEffect</a></code> attribute during the <code
   title=event-dragenter><a href="#dragenter">dragenter</a></code> and <code
   title=event-dragover><a href="#dragover">dragover</a></code> events.

  <p>The attribute must ignore any attempts to set it to a value other than
   <code title="">none</code>, <code title="">copy</code>, <code
   title="">copyLink</code>, <code title="">copyMove</code>, <code
   title="">link</code>, <code title="">linkMove</code>, <code
   title="">move</code>, <code title="">all</code>, and <code
   title="">uninitialized</code>. On getting, the attribute must return the
   last of those values that it was set to.

  <p><code><a href="#datatransfer0">DataTransfer</a></code> objects can hold
   pieces of data, each associated with a unique format. Formats are
   generally given by MIME types, with some values special-cased for legacy
   reasons.

  <p>The <dfn id=cleardata
   title=dom-DataTransfer-clearData><code>clearData(<var
   title="">format</var>)</code></dfn> method must clear the <code><a
   href="#datatransfer0">DataTransfer</a></code> object of any data
   associated with the given <var title="">format</var>. If <var
   title="">format</var> is the value "<code title="">Text</code>", then it
   must be treated as "<code title="">text/plain</code>". If the <var
   title="">format</var> is "<code title="">URL</code>", then it must be
   treated as "<code title="">text/uri-list</code>".

  <p>The <dfn id=setdata title=dom-DataTransfer-setData><code>setData(<var
   title="">format</var>, <var title="">data</var>)</code></dfn> method must
   add <var title="">data</var> to the data stored in the <code><a
   href="#datatransfer0">DataTransfer</a></code> object, labelled as being of
   the type <var title="">format</var>. This must replace any previous data
   that had been set for that format. If <var title="">format</var> is the
   value "<code title="">Text</code>", then it must be treated as "<code
   title="">text/plain</code>". If the <var title="">format</var> is "<code
   title="">URL</code>", then it must be treated as "<code
   title="">text/uri-list</code>".

  <p>The <dfn id=getdata title=dom-DataTransfer-getData><code>getData(<var
   title="">format</var>)</code></dfn> method must return the data that is
   associated with the type <var title="">format</var>, if any, and must
   return the empty string otherwise. If <var title="">format</var> is the
   value "<code title="">Text</code>", then it must be treated as "<code
   title="">text/plain</code>". If the <var title="">format</var> is "<code
   title="">URL</code>", then the data associated with the "<code
   title="">text/uri-list</code>" format must be parsed as appropriate for
   <code title="">text/uri-list</code> data, and the first URI from the list
   must be returned. If there is no data with that format, or if there is but
   it has no URIs, then the method must return the empty string. <a
   href="#refsRFC2483">[RFC2483]</a>

  <p>The <dfn id=setdragimage
   title=dom-DataTransfer-setDragImage><code>setDragImage(<var
   title="">element</var>, <var title="">x</var>, <var
   title="">y</var>)</code></dfn> method sets which element to use <a
   href="#base-dnd-feedback">to generate the drag feedback</a>. The <var
   title="">element</var> argument can be any <code>Element</code>; if it is
   an <code><a href="#img">img</a></code> element, then the user agent should
   use the element's image (at its intrinsic size) to generate the feedback,
   otherwise the user agent should base the feedback on the given element
   (but the exact mechanism for doing so is not specified).

  <p>The <dfn id=addelement
   title=dom-DataTransfer-addElement><code>addElement(<var
   title="">element</var>)</code></dfn> method is an alternative way of
   specifying how the user agent is to <a href="#base-dnd-feedback">render
   the drag feedback</a>. It adds an element to the <code><a
   href="#datatransfer0">DataTransfer</a></code> object.

  <h4 id=events1><span class=secno>5.3.2. </span>Events fired during a
   drag-and-drop action</h4>

  <p>The following events are involved in the drag-and-drop model. Whenever
   the processing model described below causes one of these events to be
   fired, the event fired must use the <code><a
   href="#dragevent">DragEvent</a></code> interface defined above, must have
   the bubbling and cancelable behaviours given in the table below, and must
   have the context information set up as described after the table.

  <table>
   <thead>
    <tr>
     <th> Event Name

     <th> Target

     <th> Bubbles?

     <th> Cancelable?

     <th> <code title=dom-DataTransfer-addElement><a
      href="#addelement">dataTransfer</a></code>

     <th> <code title=dom-DataTransfer-effectAllowed><a
      href="#effectallowed">effectAllowed</a></code>

     <th> <code title=dom-DataTransfer-dropEffect><a
      href="#dropeffect">dropEffect</a></code>

     <th> Default Action

   <tbody>
    <tr>
     <td><dfn id=dragstart title=event-dragstart><code>dragstart</code></dfn>

     <td><a href="#source0">Source node</a>

     <td>&#x2713; Bubbles

     <td>&#x2713; Cancelable

     <td>Contains <a href="#source0">source node</a> unless a selection is
      being dragged, in which case it is empty

     <td><code title="">uninitialized</code>

     <td><code title="">none</code>

     <td>Initiate the drag-and-drop operation

    <tr>
     <td><dfn id=drag title=event-drag><code>drag</code></dfn>

     <td><a href="#source0">Source node</a>

     <td>&#x2713; Bubbles

     <td>&#x2713; Cancelable

     <td>Empty

     <td><a href="#effectAllowed-initialisation">Same as last event</a>

     <td><code title="">none</code>

     <td>Continue the drag-and-drop operation

    <tr>
     <td><dfn id=dragenter title=event-dragenter><code>dragenter</code></dfn>

     <td><a href="#immediate">Immediate user selection</a> or <a
      href="#the-body0">the body element</a>

     <td>&#x2713; Bubbles

     <td>&#x2713; Cancelable

     <td>Empty

     <td><a href="#effectAllowed-initialisation">Same as last event</a>

     <td><a href="#dropEffect-initialisation">Based on
      <code>effectAllowed</code> value</a>

     <td>Reject <a href="#immediate">immediate user selection</a> as
      potential <a href="#current1" title="current target element">target
      element</a>

    <tr>
     <td><dfn id=dragleave title=event-dragleave><code>dragleave</code></dfn>

     <td><a href="#current1" title="current target element">Previous target
      element</a>

     <td>&#x2713; Bubbles

     <td>&mdash;

     <td>Empty

     <td><a href="#effectAllowed-initialisation">Same as last event</a>

     <td><code title="">none</code>

     <td>None

    <tr>
     <td><dfn id=dragover title=event-dragover><code>dragover</code></dfn>

     <td><a href="#current1">Current target element</a>

     <td>&#x2713; Bubbles

     <td>&#x2713; Cancelable

     <td>Empty

     <td><a href="#effectAllowed-initialisation">Same as last event</a>

     <td><a href="#dropEffect-initialisation">Based on
      <code>effectAllowed</code> value</a>

     <td>Reset the <a href="#current2">current drag operation</a> to "none"

    <tr>
     <td><dfn id=drop title=event-drop><code>drop</code></dfn>

     <td><a href="#current1">Current target element</a>

     <td>&#x2713; Bubbles

     <td>&#x2713; Cancelable

     <td><code>getData()</code> returns data set in <code
      title=dom-dragstart>dragstart</code> event

     <td><a href="#effectAllowed-initialisation">Same as last event</a>

     <td><a href="#current2">Current drag operation</a>

     <td>Varies

    <tr>
     <td><dfn id=dragend title=event-dragend><code>dragend</code></dfn>

     <td><a href="#source0">Source node</a>

     <td>&#x2713; Bubbles

     <td>&mdash;

     <td>Empty

     <td><a href="#effectAllowed-initialisation">Same as last event</a>

     <td><a href="#current2">Current drag operation</a>

     <td>Varies
  </table>

  <p>The <code title=dom-DragEvent-dataTransfer><a
   href="#datatransfer">dataTransfer</a></code> object's contents are empty
   except for <code title=event-dragstart><a
   href="#dragstart">dragstart</a></code> events and <code
   title=event-drop><a href="#drop">drop</a></code> events, for which the
   contents are set as described in the processing model, below.

  <p id=effectAllowed-initialisation>The <code
   title=dom-DataTransfer-effectAllowed><a
   href="#effectallowed">effectAllowed</a></code> attribute must be set to
   "<code title="">uninitialized</code>" for <code title=event-dragstart><a
   href="#dragstart">dragstart</a></code> events, and to whatever value the
   field had after the last drag-and-drop event was fired for all other
   events (only counting events fired by the user agent for the purposes of
   the drag-and-drop model described below).

  <p id=dropEffect-initialisation>The <code
   title=dom-DataTransfer-dropEffect><a
   href="#dropeffect">dropEffect</a></code> attribute must be set to "<code
   title="">none</code>" for <code title=event-dragstart><a
   href="#dragstart">dragstart</a></code>, <code title=event-drag><a
   href="#drag">drag</a></code>, <code title=event-dragleave><a
   href="#dragleave">dragleave</a></code>, and <code title=event-dragend><a
   href="#dragend">dragend</a></code> events (except when stated otherwise in
   the algorithms given in the sections below), to the value corresponding to
   the <a href="#current2">current drag operation</a> for <code
   title=event-drop><a href="#drop">drop</a></code> events, and to a value
   based on the <code title=dom-DataTransfer-effectAllowed><a
   href="#effectallowed">effectAllowed</a></code> attribute's value and to
   the drag-and-drop source, as given by the following table, for the
   remaining events (<code title=event-dragenter><a
   href="#dragenter">dragenter</a></code> and <code title=event-dragover><a
   href="#dragover">dragover</a></code>):

  <table>
   <thead>
    <tr>
     <th><code title=dom-DataTransfer-effectAllowed><a
      href="#effectallowed">effectAllowed</a></code>

     <th><code title=dom-DataTransfer-dropEffect><a
      href="#dropeffect">dropEffect</a></code>

   <tbody>
    <tr>
     <td><code title="">none</code>

     <td><code title="">none</code>

    <tr>
     <td><code title="">copy</code>, <code title="">copyLink</code>, <code
      title="">copyMove</code>, <code title="">all</code>

     <td><code title="">copy</code>

    <tr>
     <td><code title="">link</code>, <code title="">linkMove</code>

     <td><code title="">link</code>

    <tr>
     <td><code title="">move</code>

     <td><code title="">move</code>

    <tr>
     <td><code title="">uninitialized</code> when what is being dragged is a
      selection from a text field

     <td><code title="">move</code>

    <tr>
     <td><code title="">uninitialized</code> when what is being dragged is a
      selection

     <td><code title="">copy</code>

    <tr>
     <td><code title="">uninitialized</code> when what is being dragged is an
      <code><a href="#a">a</a></code> element with an <code>href</code>
      attribute

     <td><code title="">link</code>

    <tr>
     <td>Any other case

     <td><code title="">copy</code>
  </table>

  <h4 id=drag-and-drop><span class=secno>5.3.3. </span>Drag-and-drop
   processing model</h4>

  <p>When the user attempts to begin a drag operation, the user agent must
   first determine what is being dragged. If the drag operation was invoked
   on a selection, then it is the selection that is being dragged. Otherwise,
   it is the first element, going up the ancestor chain, starting at the node
   that the user tried to drag, that has the DOM attribute <code
   title=dom-draggable><a href="#draggable0">draggable</a></code> set to
   true. If there is no such element, then nothing is being dragged, the
   drag-and-drop operation is never started, and the user agent must not
   continue with this algorithm.

  <p class=note><code><a href="#img">img</a></code> elements and <code><a
   href="#a">a</a></code> elements with an <code title=attr-hyperlink-href><a
   href="#href6">href</a></code> attribute have their <code
   title=dom-draggable><a href="#draggable0">draggable</a></code> attribute
   set to true by default.

  <p>If the user agent determines that something can be dragged, a <code
   title=event-dragstart><a href="#dragstart">dragstart</a></code> event must
   then be fired.

  <p>If it is a selection that is being dragged, then this event must be
   fired on the node that the user started the drag on (typically the text
   node that the user originally clicked). If the user did not specify a
   particular node, for example if the user just told the user agent to begin
   a drag of "the selection", then the event must be fired on the deepest
   node that is a common ancestor of all parts of the selection.

  <p>If it is not a selection that is being dragged, then the event must be
   fired on the element that is being dragged.

  <p>The node on which the event is fired is the <dfn id=source0>source
   node</dfn>. Multiple events are fired on this node during the course of
   the drag-and-drop operation.

  <p>If it is a selection that is being dragged, the <code
   title=dom-DragEvent-dataTransfer><a
   href="#datatransfer">dataTransfer</a></code> member of the event must be
   created with no nodes. Otherwise, it must be created containing just the
   <a href="#source0">source node</a>. Script can use the <code
   title=dom-DataTransfer-addElement><a
   href="#addelement">addElement()</a></code> method to add further elements
   to the list of what is being dragged.

  <p>If it is a selection that is being dragged, the <code
   title=dom-DragEvent-dataTransfer><a
   href="#datatransfer">dataTransfer</a></code> member of the event must have
   the text of the selection added to it as the data associated with the
   <code title="">text/plain</code> format. Otherwise, if it is an <code><a
   href="#img">img</a></code> element being dragged, then the value of the
   element's <code title=dom-img-src><a href="#src0">src</a></code> DOM
   attribute must be added, associated with the <code
   title="">text/uri-list</code> format. Otherwise, if it is an <code><a
   href="#a">a</a></code> element being dragged, then the value of the
   element's <code title=dom-a-href><a href="#href3">href</a></code> DOM
   attribute must be added, associated with the <code
   title="">text/uri-list</code> format. Otherwise, no data is added to the
   object by the user agent.

  <p>If the event is canceled, then the drag-and-drop operation must not
   occur; the user agent must not continue with this algorithm.

  <p>If it is not canceled, then the drag-and-drop operation must be
   initiated.

  <p class=note>Since events with no event handlers registered are, almost by
   definition, never canceled, drag-and-drop is always available to the user
   if the author does not specifically prevent it.

  <p id=base-dnd-feedback>The drag-and-drop feedback must be generated from
   the first of the following sources that is available:

  <ol>
   <li>The element specified in the last call to the <code
    title=dom-DataTransfer-setDragImage><a
    href="#setdragimage">setDragImage()</a></code> method of the <code
    title=dom-DragEvent-dataTransfer><a
    href="#datatransfer">dataTransfer</a></code> object of the <code
    title=event-dragstart><a href="#dragstart">dragstart</a></code> event, if
    the method was called. In visual media, if this is used, the <var
    title="">x</var> and <var title="">y</var> arguments that were passed to
    that method should be used as hints for where to put the cursor relative
    to the resulting image. The values are expressed as distances in CSS
    pixels from the left side and from the top side of the image
    respectively. <a href="#refsCSS21">[CSS21]</a></li>
   <!--
   CSS3 UNITS would be better -->

   <li>The elements that were added to the <code
    title=dom-DragEvent-dataTransfer><a
    href="#datatransfer">dataTransfer</a></code> object, both before the
    event was fired, and during the handling of the event using the <code
    title=dom-DataTransfer-addElement><a
    href="#addelement">addElement()</a></code> method, if any such elements
    were indeed added.

   <li>The selection that the user is dragging.
  </ol>
  <!-- XXX xref also link to the section that explains how to
  render drag-and-drop, :drag, :drop, etc. Safari has a pseudo-class
  that it uses to render an element off-screen to use as the drag
  feedback. -->

  <p>The user agent must take a note of <a href="#setdata"
   title=dom-DataTransfer-setData>the data that was placed</a> in the <code
   title=dom-DragEvent-dataTransfer><a
   href="#datatransfer">dataTransfer</a></code> object. This data will be
   made available again when the <code title=event-drop><a
   href="#drop">drop</a></code> event is fired.

  <p>From this point until the end of the drag-and-drop operation, device
   input events (e.g. mouse and keyboard events) must be suppressed. In
   addition, the user agent must track all DOM changes made during the
   drag-and-drop operation, and add them to its <a href="#undo">undo
   history</a> as one atomic operation once the drag-and-drop operation has
   ended.

  <p>During the drag operation, the element directly indicated by the user as
   the drop target is called the <dfn id=immediate>immediate user
   selection</dfn>. (Only elements can be selected by the user; other nodes
   must not be made available as drop targets.) However, the <a
   href="#immediate">immediate user selection</a> is not necessarily the <dfn
   id=current1>current target element</dfn>, which is the element currently
   selected for the drop part of the drag-and-drop operation. The <a
   href="#immediate">immediate user selection</a> changes as the user selects
   different elements (either by pointing at them with a pointing device, or
   by selecting them in some other way). The <a href="#current1">current
   target element</a> changes when the <a href="#immediate">immediate user
   selection</a> changes, based on the results of event handlers in the
   document, as described below.

  <p>Both the <a href="#current1">current target element</a> and the <a
   href="#immediate">immediate user selection</a> can be null, which means no
   target element is selected. They can also both be elements in other
   (DOM-based) documents, or other (non-Web) programs altogether. (For
   example, a user could drag text to a word-processor.) The <a
   href="#current1">current target element</a> is initially null.

  <p>In addition, there is also a <dfn id=current2>current drag
   operation</dfn>, which can take on the values "none", "copy", "link", and
   "move". Initially it has the value "none". It is updated by the user agent
   as described in the steps below.

  <p>User agents must, every 350ms (&#xB1;200ms), perform the following steps
   in sequence. (If the user agent is still performing the previous iteration
   of the sequence when the next iteration becomes due, the user agent must
   not execute the overdue iteration, effectively "skipping missed frames" of
   the drag-and-drop operation.)

  <ol>
   <li>
    <p>First, the user agent must fire a <code title=event-drag><a
     href="#drag">drag</a></code> event at the <a href="#source0">source
     node</a>. If this event is canceled, the user agent must set the <a
     href="#current2">current drag operation</a> to none (no drag operation).</p>

   <li>
    <p>Next, if the <code title=event-drag><a href="#drag">drag</a></code>
     event was not canceled and the user has not ended the drag-and-drop
     operation, the user agent must check the state of the drag-and-drop
     operation, as follows:</p>

    <ol>
     <li>
      <p>First, if the user is indicating a different <a
       href="#immediate">immediate user selection</a> than during the last
       iteration (or if this is the first iteration), and if this <a
       href="#immediate">immediate user selection</a> is not the same as the
       <a href="#current1">current target element</a>, then the <a
       href="#current1">current target element</a> must be updated, as
       follows:</p>

      <ol>
       <li>
        <p>If the new <a href="#immediate">immediate user selection</a> is
         null, or is in a non-DOM document or application, then set the <a
         href="#current1">current target element</a> to the same value.</p>

       <li>
        <p>Otherwise, the user agent must fire a <code
         title=event-dragenter><a href="#dragenter">dragenter</a></code>
         event at the <a href="#immediate">immediate user selection</a>.</p>

       <li>
        <p>If the event is canceled, then the <a href="#current1">current
         target element</a> must be set to the <a href="#immediate">immediate
         user selection</a>.</p>

       <li>
        <p>Otherwise, if the <a href="#current1">current target element</a>
         is not <a href="#the-body0">the body element</a>, the user agent
         must fire a <code title=event-dragenter><a
         href="#dragenter">dragenter</a></code> event at <a
         href="#the-body0">the body element</a>, and the <a
         href="#current1">current target element</a> must be set to <a
         href="#the-body0">the body element</a>, regardless of whether that
         event was canceled or not. (If <a href="#the-body0">the body
         element</a> is null, then the <a href="#current1">current target
         element</a> would be set to null too in this case, it wouldn't be
         set to the <code>Document</code> object.)</p>
      </ol>

     <li>
      <p>If the previous step caused the <a href="#current1">current target
       element</a> to change, and if the previous target element was not null
       or a part of a non-DOM document, the user agent must fire a <code
       title=event-dragleave><a href="#dragleave">dragleave</a></code> event
       at the previous target element.</p>

     <li>
      <p>If the <a href="#current1">current target element</a> is a DOM
       element, the user agent must fire a <code title=event-dragover><a
       href="#dragover">dragover</a></code> event at this <a
       href="#current1">current target element</a>.</p>

      <p>If the <code title=event-dragover><a
       href="#dragover">dragover</a></code> event is canceled, the <a
       href="#current2">current drag operation</a> must be reset to "none".</p>

      <p>Otherwise, the <a href="#current2">current drag operation</a> must
       be set based on the values the <code
       title=dom-DataTransfer-effectAllowed><a
       href="#effectallowed">effectAllowed</a></code> and <code
       title=dom-DataTransfer-dropEffect><a
       href="#dropeffect">dropEffect</a></code> attributes of the <code
       title=dom-DragEvent-dataTransfer><a
       href="#datatransfer">dataTransfer</a></code> object had after the
       event was handled, as per the following table:</p>

      <table>
       <thead>
        <tr>
         <th><code title=dom-DataTransfer-effectAllowed><a
          href="#effectallowed">effectAllowed</a></code>

         <th><code title=dom-DataTransfer-dropEffect><a
          href="#dropeffect">dropEffect</a></code>

         <th>Drag operation

       <tbody>
        <tr>
         <td><code title="">uninitialized</code>, <code title="">copy</code>,
          <code title="">copyLink</code>, <code title="">copyMove</code>, or
          <code title="">all</code>

         <td><code title="">copy</code>

         <td>"copy"

        <tr>
         <td><code title="">uninitialized</code>, <code title="">link</code>,
          <code title="">copyLink</code>, <code title="">linkMove</code>, or
          <code title="">all</code>

         <td><code title="">link</code>

         <td>"link"

        <tr>
         <td><code title="">uninitialized</code>, <code title="">move</code>,
          <code title="">copyMove</code>, <code title="">linkMove</code>, or
          <code title="">all</code>

         <td><code title="">move</code>

         <td>"move"

        <tr>
         <td colspan=2>Any other case

         <td>"none"
      </table>

      <p>Then, regardless of whether the <code title=event-dragover><a
       href="#dragover">dragover</a></code> event was canceled or not, the
       drag feedback (e.g. the mouse cursor) must be updated to match the <a
       href="#current2">current drag operation</a>, as follows:</p>

      <table>
       <thead>
        <tr>
         <th>Drag operation

         <th>Feedback

       <tbody>
        <tr>
         <td>"copy"

         <td>Data will be copied if dropped here.

        <tr>
         <td>"link"

         <td>Data will be linked if dropped here.

        <tr>
         <td>"move"

         <td>Data will be moved if dropped here.

        <tr>
         <td>"none"

         <td>No operation allowed, dropping here will cancel the
          drag-and-drop operation.
      </table>

     <li>
      <p>Otherwise, if the <a href="#current1">current target element</a> is
       not a DOM element, the user agent must use platform-specific
       mechanisms to determine what drag operation is being performed (none,
       copy, link, or move). This sets the <em><a href="#current2">current
       drag operation</a></em>.</p>
    </ol>

   <li>
    <p>Otherwise, if the user ended the drag-and-drop operation (e.g. by
     releasing the mouse button in a mouse-driven drag-and-drop interface),
     or if the <code title=event-drag><a href="#drag">drag</a></code> event
     was canceled, then this will be the last iteration. The user agent must
     follow the following steps, then stop looping.</p>

    <ol>
     <li>
      <p>If the <a href="#current2">current drag operation</a> is none (no
       drag operation), or, if the user ended the drag-and-drop operation by
       canceling it (e.g. by hitting the <kbd>Escape</kbd> key), or if the <a
       href="#current1">current target element</a> is null, then the drag
       operation failed. If the <a href="#current1">current target
       element</a> is a DOM element, the user agent must fire a <code
       title=event-dragleave><a href="#dragleave">dragleave</a></code> event
       at it; otherwise, if it is not null, it must use platform-specific
       conventions for drag cancellation.</p>

     <li>
      <p>Otherwise, the drag operation was as success. If the <a
       href="#current1">current target element</a> is a DOM element, the user
       agent must fire a <code title=event-drop><a
       href="#drop">drop</a></code> event at it; otherwise, it must use
       platform-specific conventions for indicating a drop.</p>

      <p>When the target is a DOM element, the <code
       title=dom-DataTransfer-dropEffect><a
       href="#dropeffect">dropEffect</a></code> attribute of the event's
       <code title=dom-DragEvent-dataTransfer><a
       href="#datatransfer">dataTransfer</a></code> object must be given the
       value representing the <a href="#current2">current drag operation</a>
       (<code title="">copy</code>, <code title="">link</code>, or <code
       title="">move</code>), and the object must be set up so that the <code
       title=dom-DataTransfer-getData><a href="#getdata">getData()</a></code>
       method will return the data that was added during the <code
       title=event-dragstart><a href="#dragstart">dragstart</a></code> event.</p>

      <p>If the event is canceled, the <a href="#current2">current drag
       operation</a> must be set to the value of the <code
       title=dom-DataTransfer-dropEffect><a
       href="#dropeffect">dropEffect</a></code> attribute of the event's
       <code title=dom-DragEvent-dataTransfer><a
       href="#datatransfer">dataTransfer</a></code> object as it stood after
       the event was handled.</p>

      <p>Otherwise, the event is not canceled, and the user agent must
       perform the event's default action, which depends on the exact target
       as follows:</p>

      <dl class=switch>
       <dt>If the <a href="#current1">current target element</a> is a text
        field (e.g. <code>textarea</code>, or an <code>input</code> element
        with <code title="">type="text"</code><!--XXX xref-->)

       <dd>The user agent must insert the data associated with the
        <code>text/plain</code> format, if any, into the text field in a
        manner consistent with platform-specific conventions (e.g. inserting
        it at the current mouse cursor position, or inserting it at the end
        of the field).

       <dt>Otherwise

       <dd>Reset the <a href="#current2">current drag operation</a> to
        "none".
      </dl>

     <li>
      <p>Finally, the user agent must fire a <code title=event-dragend><a
       href="#dragend">dragend</a></code> event at the <a
       href="#source0">source node</a>, with the <code
       title=dom-DataTransfer-dropEffect><a
       href="#dropeffect">dropEffect</a></code> attribute of the event's
       <code title=dom-DragEvent-dataTransfer><a
       href="#datatransfer">dataTransfer</a></code> object being set to the
       value corresponding to the <a href="#current2">current drag
       operation</a>.</p>

      <p class=note>The <a href="#current2">current drag operation</a> can
       change during the processing of the <code title=event-drop><a
       href="#drop">drop</a></code> event, if one was fired.</p>

      <p>The event is not cancelable. After the event has been handled, the
       user agent must act as follows:</p>

      <dl class=switch>
       <dt>If the <a href="#current1">current target element</a> is a text
        field (e.g. <code>textarea</code>, or an <code>input</code> element
        with <code title="">type="text"</code><!--XXX xref-->), and a <code
        title=event-drop><a href="#drop">drop</a></code> event was fired in
        the previous step, and the <a href="#current2">current drag
        operation</a> is "move", and the source of the drag-and-drop
        operation is a selection in the DOM

       <dd>The user agent should delete the range representing the dragged
        selection from the DOM.

       <dt>If the <a href="#current1">current target element</a> is a text
        field (e.g. <code>textarea</code>, or an <code>input</code> element
        with <code title="">type="text"</code><!--XXX xref-->), and a <code
        title=event-drop><a href="#drop">drop</a></code> event was fired in
        the previous step, and the <a href="#current2">current drag
        operation</a> is "move", and the source of the drag-and-drop
        operation is a selection in a text field

       <dd>The user agent should delete the dragged selection from the
        relevant text field.

       <dt>Otherwise

       <dd>The event has no default action.
      </dl>
    </ol>
  </ol>

  <h5 id=when-the><span class=secno>5.3.3.1. </span>When the drag-and-drop
   operation starts or ends in another document</h5>

  <p>The model described above is independent of which <code>Document</code>
   object the nodes involved are from; the events must be fired as described
   above and the rest of the processing model must be followed as described
   above, irrespective of how many documents are involved in the operation.

  <h5 id=when-the0><span class=secno>5.3.3.2. </span>When the drag-and-drop
   operation starts or ends in another application</h5>

  <p>If the drag is initiated in another application, the <a
   href="#source0">source node</a> is not a DOM node, and the user agent must
   use platform-specific conventions instead when the requirements above
   involve the source node. User agents in this situation must act as if the
   dragged data had been added to the <code><a
   href="#datatransfer0">DataTransfer</a></code> object when the drag
   started, even though no <code title=event-dragstart><a
   href="#dragstart">dragstart</a></code> event was actually fired; user
   agents must similarly use platform-specific conventions when deciding on
   what drag feedback to use.

  <p>If a drag is started in a document but ends in another application, then
   the user agent must instead replace the parts of the processing model
   relating to handling the <em>target</em> according to platform-specific
   conventions.

  <p>In any case, scripts running in the context of the document must not be
   able to distinguish the case of a drag-and-drop operation being started or
   ended in another application from the case of a drag-and-drop operation
   being started or ended in another document from another domain.

  <h4 id=the-draggable><span class=secno>5.3.4. </span>The <dfn id=draggable
   title=attr-draggable><code>draggable</code></dfn> attribute</h4>

  <p>All elements may have the <code title=attr-draggable><a
   href="#draggable">draggable</a></code> content attribute set. The <code
   title=attr-draggable><a href="#draggable">draggable</a></code> attribute
   is an <a href="#enumerated">enumerated attribute</a>. It has three states.
   The first state is <em>true</em> and it has the keyword <code
   title="">true</code>. The second state is <em>false</em> and it has the
   keyword <code title="">false</code>. The third state is <em>auto</em>; it
   has no keywords but it is the <em>missing value default</em>.

  <p>The <dfn id=draggable0 title=dom-draggable><code>draggable</code></dfn>
   DOM attribute, whose value depends on the content attribute's in the way
   described below, controls whether or not the element is draggable.
   Generally, only text selections are draggable, but elements whose <code
   title=dom-draggable><a href="#draggable0">draggable</a></code> DOM
   attribute is true become draggable as well.

  <p>If an element's <code title=attr-draggable><a
   href="#draggable">draggable</a></code> content attribute has the state
   <em>true</em>, the <code title=dom-draggable><a
   href="#draggable0">draggable</a></code> DOM attribute must return true.

  <p>Otherwise, if the element's <code title=attr-draggable><a
   href="#draggable">draggable</a></code> content attribute has the state
   <em>false</em>, the <code title=dom-draggable><a
   href="#draggable0">draggable</a></code> DOM attribute must return false.

  <p>Otherwise, the element's <code title=attr-draggable><a
   href="#draggable">draggable</a></code> content attribute has the state
   <em>auto</em>. If the element is an <code><a href="#img">img</a></code>
   element, or, if the element is an <code><a href="#a">a</a></code> element
   with an <code title=attr-hyperlink-href><a href="#href6">href</a></code>
   content attribute, the <code title=dom-draggable><a
   href="#draggable0">draggable</a></code> DOM attribute must return true.

  <p>Otherwise, the <code title=dom-draggable><a
   href="#draggable0">draggable</a></code> DOM must return false.

  <p>If the <code title=dom-draggable><a
   href="#draggable0">draggable</a></code> DOM attribute is set to the value
   false, the <code title=attr-draggable><a
   href="#draggable">draggable</a></code> content attribute must be set to
   the literal value <code title="">false</code>. If the <code
   title=dom-draggable><a href="#draggable0">draggable</a></code> DOM
   attribute is set to the value true, the <code title=attr-draggable><a
   href="#draggable">draggable</a></code> content attribute must be set to
   the literal value <code title="">true</code>.

  <h4 id=copy-and><span class=secno>5.3.5. </span>Copy and paste</h4>

  <p>Copy-and-paste is a form of drag-and-drop: the "copy" part is equivalent
   to dragging content to another application (the "clipboard"), and the
   "paste" part is equivalent to dragging content <em>from</em> another
   application.

  <p>Select-and-paste (a model used by mouse operations in the X Window
   System) is equivalent to a drag-and-drop operation where the source is the
   selection.

  <h5 id=copy-to><span class=secno>5.3.5.1. </span>Copy to clipboard</h5>

  <p>When the user invokes a copy operation, the user agent must act as if
   the user had invoked a drag on the current selection. If the drag-and-drop
   operation initiates, then the user agent must act as if the user had
   indicated (as the <a href="#immediate">immediate user selection</a>) a
   hypothetical application representing the clipbroad. Then, the user agent
   must act as if the user had ended the drag-and-drop operation without
   canceling it. If the drag-and-drop operation didn't get canceled, the user
   agent should then follow the relevant platform-specific conventions for
   copy operations (e.g. updating the clipboard).

  <h5 id=cut-to><span class=secno>5.3.5.2. </span>Cut to clipboard</h5>

  <p>When the user invokes a cut operation, the user agent must act as if the
   user had invoked a copy operation (see the previous section), followed, if
   the copy was completed successfully, by <a
   href="#contenteditable-delete">a selection delete operation</a>.

  <h5 id=paste><span class=secno>5.3.5.3. </span>Paste from clipboard</h5>

  <p>When the user invokes a clipboard paste operation, the user agent must
   act as if the user had invoked a drag on a hypothetical application
   representing the clipboard, setting the data associated with the drag as
   the text from the keyboard (either as <code title="">text/plain</code> or
   <code>text/uri-list</code>). If the contents of the clipboard cannot be
   represented as text or URIs, then the paste operation must not have any
   effect.

  <p>Then, the user agent must act as if the user had indicated (as the <a
   href="#immediate">immediate user selection</a>) the element with the
   keyboard focus, and then ended the drag-and-drop operation without
   canceling it.

  <h5 id=paste0><span class=secno>5.3.5.4. </span>Paste from selection</h5>

  <p>When the user invokes a selection paste operation, the user agent must
   act as if the user had invoked a drag on the current selection, then
   indicated (as the <a href="#immediate">immediate user selection</a>) the
   element with the keyboard focus, and then ended the drag-and-drop
   operation without canceling it.

  <p>If the contents of the selection cannot be represented as text or URIs,
   then the paste operation must not have any effect.

  <h4 id=security7><span class=secno>5.3.6. </span>Security risks in the
   drag-and-drop model</h4>

  <p>User agents must not make the data added to the <code><a
   href="#datatransfer0">DataTransfer</a></code> object during the <code
   title=event-dragstart><a href="#dragstart">dragstart</a></code> event
   available to scripts until the <code title=event-drop><a
   href="#drop">drop</a></code> event, because otherwise, if a user were to
   drag sensitive information from one document to a second document,
   crossing a hostile third document in the process, the hostile document
   could intercept the data.

  <p>For the same reason, user agents must only consider a drop to be
   successful if the user specifically ended the drag operation &mdash; if
   any scripts end the drag operation, it must be considered unsuccessful
   (canceled) and the <code title=event-drop><a href="#drop">drop</a></code>
   event must not be fired.

  <p>User agents should take care to not start drag-and-drop operations in
   response to script actions. For example, in a mouse-and-window
   environment, if a script moves a window while the user has his mouse
   button depressed, the UA would not consider that to start a drag. This is
   important because otherwise UAs could cause data to be dragged from
   sensitive sources and dropped into hostile documents without the user's
   consent.

  <h3 id=undo><span class=secno>5.4. </span><dfn id=undo-history>Undo
   history</dfn></h3>

  <p class=big-issue>There has got to be a better way of doing this, surely.

  <p>The user agent must associate an <dfn id=undo-transaction>undo
   transaction history</dfn> with each <code><a
   href="#htmldocument">HTMLDocument</a></code> object.

  <p>The <a href="#undo-transaction">undo transaction history</a> is a list
   of entries. The entries are of two type: <a href="#dom-changes">DOM
   changes</a> and <a href="#undo-object" title="undo object">undo
   objects</a>.

  <p>Each <dfn id=dom-changes>DOM changes</dfn> entry in the <a
   href="#undo-transaction">undo transaction history</a> consists of batches
   of one or more of the following:

  <ul>
   <li>Changes to the <a href="#content">content attributes</a> of an
    <code>Element</code> node.

   <li>Changes to the <a href="#dom-attributes">DOM attributes</a> of a
    <code>Node</code>.</li>
   <!-- XXX uh, these change on their own, so
   clearly this isn't going to fly. Which DOM attributes, exactly? -->

   <li>Changes to the DOM hierarchy of nodes that are descendants of the
    <code><a href="#htmldocument">HTMLDocument</a></code> object
    (<code>parentNode</code>, <code>childNodes</code>).
  </ul>

  <p><dfn id=undo-object>Undo object</dfn> entries consist of objects
   representing state that scripts running in the document are managing. For
   example, a Web mail application could use an <a href="#undo-object">undo
   object</a> to keep track of the fact that a user has moved an e-mail to a
   particular folder, so that the user can undo the action and have the
   e-mail return to its former location.

  <p>Broadly speaking, <a href="#dom-changes">DOM changes</a> entries are
   handled by the UA in response to user edits of form controls and
   <span>editing hosts</span> on the page, and <a href="#undo-object">undo
   object</a> entries are handled by script in response to higher-level user
   actions (such as interactions with server-side state, or in the
   implementation of a drawing tool).

  <h4 id=the-undomanager><span class=secno>5.4.1. </span>The <code><a
   href="#undomanager">UndoManager</a></code> interface</h4>

  <div class=big-issue>
   <p>This API sucks. Seriously. It's a terrible API. Really bad. I hate it.
    Here are the requirements:</p>

   <ul>
    <li>Has to cope with cases where the server has undo state already when
     the page is loaded, that can be stuffed into the undo buffer onload.

    <li>Has to support undo/redo.

    <li>Has to cope with the "undo" action being "contact the server and tell
     it to undo", rather than it being the opposite of the "redo" action.

    <li>Has to cope with some undo states expiring from the undo history
     (e.g. server can only remember one undelete action) but other states not
     expiring (e.g. client can undo arbitrary amounts of local edits).
   </ul>
  </div>

  <p>To manage <a href="#undo-object">undo object</a> entries in the <a
   href="#undo-transaction">undo transaction history</a>, the <code><a
   href="#undomanager">UndoManager</a></code> interface can be used:

  <pre class=idl>interface <dfn id=undomanager>UndoManager</dfn> {
  unsigned long <a href="#adddata" title=dom-UndoManager-add>add</a>(in DOMObject data, in DOMStrong title);
  void <a href="#remove1" title=dom-UndoManager-remove>remove</a>(in unsigned long index);
  void <a href="#clearundo" title=dom-UndoManager-clearUndo>clearUndo</a>();
  void <a href="#clearredo" title=dom-UndoManager-clearRedo>clearRedo</a>();
  DOMObject <a href="#itemn" title=dom-UndoManager-item>item</a>(in unsigned long index);
  readonly attribute unsigned long <a href="#length9" title=dom-UndoManager-length>length</a>;
  readonly attribute unsigned long <a href="#position0" title=dom-UndoManager-position>position</a>;
};</pre>

  <p>The <dfn id=undomanager0
   title=dom-undoManager><code>undoManager</code></dfn> attribute of the
   <code><a href="#window">Window</a></code> interface must return the object
   implementing the <code><a href="#undomanager">UndoManager</a></code>
   interface for that <code><a href="#window">Window</a></code> object's
   associated <code><a href="#htmldocument">HTMLDocument</a></code> object.

  <p>In the ECMAScript DOM binding, objects implementing this interface must
   also support being dereferenced using the square bracket notation, such
   that dereferencing with an integer index is equivalent to invoking the
   <code title=dom-UndoManager-item><a href="#itemn">item()</a></code> method
   with that index (e.g. <code title="">undoManager[1]</code> returns the
   same as <code title="">undoManager.item(1)</code>).

  <p><code><a href="#undomanager">UndoManager</a></code> objects represent
   their document's <a href="#undo-transaction">undo transaction history</a>.
   Only <a href="#undo-object">undo object</a> entries are visible with this
   API, but this does not mean that <a href="#dom-changes">DOM changes</a>
   entries are absent from the <a href="#undo-transaction">undo transaction
   history</a>.

  <p>The <dfn id=length9
   title=dom-UndoManager-length><code>length</code></dfn> attribute must
   return the number of <a href="#undo-object">undo object</a> entries in the
   <a href="#undo-transaction">undo transaction history</a>.

  <p>The <dfn id=itemn title=dom-UndoManager-item><code>item(<var
   title="">n</var>)</code></dfn> method must return the <var
   title="">n</var>th <a href="#undo-object">undo object</a> entry in the <a
   href="#undo-transaction">undo transaction history</a>.

  <p>The <a href="#undo-transaction">undo transaction history</a> has a <dfn
   id=current3 title="undo position">current position</dfn>. This is the
   position between two entries in the <a href="#undo-transaction">undo
   transaction history</a>'s list where the previous entry represents what
   needs to happen if the user invokes the "undo" command (the "undo" side,
   lower numbers), and the next entry represents what needs to happen if the
   user invokes the "redo" command (the "redo" side, higher numbers).

  <p>The <dfn id=position0
   title=dom-UndoManager-position><code>position</code></dfn> attribute must
   return the index of the <a href="#undo-object">undo object</a> entry
   nearest to the <a href="#current3">undo position</a>, on the "redo" side.
   If there are no <a href="#undo-object">undo object</a> entries on the
   "redo" side, then the attribute must return the same as the <code
   title=dom-UndoManager-length><a href="#length9">length</a></code>
   attribute. If there are no <a href="#undo-object">undo object</a> entries
   on the "undo" side of the <a href="#current3">undo position</a>, the <code
   title=dom-UndoManager-position><a href="#position0">position</a></code>
   attribute returns zero.

  <p class=note>Since the <a href="#undo-transaction">undo transaction
   history</a> contains both <a href="#undo-object">undo object</a> entries
   and <a href="#dom-changes">DOM changes</a> entries, but the <code
   title=dom-UndoManager-position><a href="#position0">position</a></code>
   attribute only returns indices relative to <a href="#undo-object">undo
   object</a> entries, it is possible for several "undo" or "redo" actions to
   be performed without the value of the <code
   title=dom-UndoManager-position><a href="#position0">position</a></code>
   attribute changing.

  <p>The <dfn id=adddata title=dom-UndoManager-add><code>add(<var
   title="">data</var>, <var title="">title</var>)</code></dfn> method's
   behaviour depends on the current state. Normally, it must insert the <var
   title="">data</var> object passed as an argument into the <a
   href="#undo-transaction">undo transaction history</a> immediately before
   the <a href="#current3">undo position</a>, optionally remembering the
   given <var title="">title</var> to use in the UI. If the method is called
   <a href="#undo-moving0" title=do-undo>during an undo operation</a>,
   however, the object must instead be added immediately <em>after</em> the
   <a href="#current3">undo position</a>.

  <p>If the method is called and there is neither <a href="#undo-moving0"
   title=do-undo>an undo operation in progress</a> nor <a
   href="#redo-moving0" title=do-redo>a redo operation in progress</a> then
   any entries in the <a href="#undo-transaction">undo transaction
   history</a> after the <a href="#current3">undo position</a> must be
   removed (as if <code title=dom-UndoManager-clearRedo><a
   href="#clearredo">clearRedo()</a></code> had been called).

  <p class=big-issue>We could fire events when someone adds something to the
   undo history -- one event per undo object entry before the position (or
   after, during redo addition), allowing the script to decide if that entry
   should remain or not. Or something. Would make it potentially easier to
   expire server-held state when the server limitations come into play.</p>
  <!-- XXX note on expiring undo in case server can only do one level undo -->

  <p>The <dfn id=remove1 title=dom-UndoManager-remove><code>remove(<var
   title="">index</var>)</code></dfn> method must remove the <a
   href="#undo-object">undo object</a> entry with the specified <var
   title="">index</var>. If the index is less than zero or greater than or
   equal to <code title=dom-UndoManager-length><a
   href="#length9">length</a></code> then the method must raise an
   <code>INDEX_SIZE_ERR</code> exception. <a href="#dom-changes">DOM
   changes</a> entries are unaffected by this method.

  <p>The <dfn id=clearundo
   title=dom-UndoManager-clearUndo><code>clearUndo()</code></dfn> method must
   remove all entries in the <a href="#undo-transaction">undo transaction
   history</a> before the <a href="#current3">undo position</a>, be they <a
   href="#dom-changes">DOM changes</a> entries or <a href="#undo-object">undo
   object</a> entries.

  <p>The <dfn id=clearredo
   title=dom-UndoManager-clearRedo><code>clearRedo()</code></dfn> method must
   remove all entries in the <a href="#undo-transaction">undo transaction
   history</a> after the <a href="#current3">undo position</a>, be they <a
   href="#dom-changes">DOM changes</a> entries or <a href="#undo-object">undo
   object</a> entries.

  <p class=big-issue>Another idea is to have a way for scripts to say
   "startBatchingDOMChangesForUndo()" and after that the changes to the DOM
   go in as if the user had done them.

  <h4 id=undo-moving><span class=secno>5.4.2. </span><dfn id=undo-moving0
   title=do-undo>Undo: moving back in the undo transaction history</dfn></h4>

  <p>When the user invokes an undo operation, or when the <code
   title=dom-document-execCommand><a
   href="#execCommand">execCommand()</a></code> method is called with the
   <code title=command-undo><a href="#undo1">undo</a></code> command, the
   user agent must perform an undo operation.

  <p>If the <a href="#current3">undo position</a> is at the start of the <a
   href="#undo-transaction">undo transaction history</a>, then the user agent
   must do nothing.

  <p>If the entry immediately before the <a href="#current3">undo
   position</a> is a <a href="#dom-changes">DOM changes</a> entry, then the
   user agent must remove that <a href="#dom-changes">DOM changes</a> entry,
   reverse the DOM changes that were listed in that entry, and, if the
   changes were reversed with no problems, add a new <a
   href="#dom-changes">DOM changes</a> entry (consisting of the opposite of
   those DOM changes) to the <a href="#undo-transaction">undo transaction
   history</a> on the other side of the <a href="#current3">undo
   position</a>.

  <p>If the DOM changes cannot be undone (e.g. because the DOM state is no
   longer consistent with the changes represented in the entry), then the
   user agent must simply remove the <a href="#dom-changes">DOM changes</a>
   entry, without doing anything else.

  <p>If the entry immediately before the <a href="#current3">undo
   position</a> is an <a href="#undo-object">undo object</a> entry, then the
   user agent must first remove that <a href="#undo-object">undo object</a>
   entry from the <a href="#undo-transaction">undo transaction history</a>,
   and then must fire an <code title=event-undo><a
   href="#undo0">undo</a></code> event on the <code>Document</code> object,
   using the <a href="#undo-object">undo object</a> entry's associated undo
   object as the event's data.

  <p>Any calls to <code title=dom-undoManager-add><a
   href="#adddata">add()</a></code> while the event is being handled will be
   used to populate the redo history, and will then be used if the user
   invokes the "redo" command to undo his undo.

  <h4 id=redo-moving><span class=secno>5.4.3. </span><dfn id=redo-moving0
   title=do-redo>Redo: moving forward in the undo transaction history</dfn></h4>

  <p>When the user invokes a redo operation, or when the <code
   title=dom-document-execCommand><a
   href="#execCommand">execCommand()</a></code> method is called with the
   <code title=command-redo><a href="#redo0">redo</a></code> command, the
   user agent must perform a redo operation.

  <p>This is mostly the opposite of an <a href="#undo-moving0"
   title=do-undo>undo operation</a>, but the full definition is included here
   for completeness.

  <p>If the <a href="#current3">undo position</a> is at the end of the <a
   href="#undo-transaction">undo transaction history</a>, then the user agent
   must do nothing.

  <p>If the entry immediately after the <a href="#current3">undo position</a>
   is a <a href="#dom-changes">DOM changes</a> entry, then the user agent
   must remove that <a href="#dom-changes">DOM changes</a> entry, reverse the
   DOM changes that were listed in that entry, and, if the changes were
   reversed with no problems, add a new <a href="#dom-changes">DOM
   changes</a> entry (consisting of the opposite of those DOM changes) to the
   <a href="#undo-transaction">undo transaction history</a> on the other side
   of the <a href="#current3">undo position</a>.

  <p>If the DOM changes cannot be redone (e.g. because the DOM state is no
   longer consistent with the changes represented in the entry), then the
   user agent must simply remove the <a href="#dom-changes">DOM changes</a>
   entry, without doing anything else.

  <p>If the entry immediately after the <a href="#current3">undo position</a>
   is an <a href="#undo-object">undo object</a> entry, then the user agent
   must first remove that <a href="#undo-object">undo object</a> entry from
   the <a href="#undo-transaction">undo transaction history</a>, and then
   must fire a <code title=event-undo><a href="#undo0">redo</a></code> event
   on the <code>Document</code> object, using the <a href="#undo-object">undo
   object</a> entry's associated undo object as the event's data.

  <h4 id=the-undomanagerevent><span class=secno>5.4.4. </span>The <code><a
   href="#undomanagerevent">UndoManagerEvent</a></code> interface and the
   <code title=event-undo><a href="#undo0">undo</a></code> and <code
   title=event-redo><a href="#redo">redo</a></code> events</h4>

  <pre
   class=idl>interface <dfn id=undomanagerevent>UndoManagerEvent</dfn> : Event {
  readonly attribute DOMObject <a href="#data3" title=dom-UndoManagerEvent-data>data</a>;
  void <a href="#initundomanagerevent" title=dom-UndoManagerEvent-initUndoManagerEvent>initUndoManagerEvent</a>(in DOMString typeArg, in boolean canBubbleArg, in boolean cancelableArg, in DOMObject dataArg);
  void <span title=dom-UndoManagerEvent-initUndoManagerEventNS>initUndoManagerEventNS</span>(in DOMString namespaceURIArg, in DOMString typeArg, in boolean canBubbleArg, in boolean cancelableArg, in DOMObject dataArg);
};</pre>

  <p>The <dfn id=initundomanagerevent
   title=dom-UndoManagerEvent-initUndoManagerEvent><code>initUndoManagerEvent()</code></dfn>
   and <dfn id=initundomanagereventns><code
   title=dom-UndoManagerEvent-initUndoManagerEventNS>initUndoManagerEventNS()</code></dfn>
   methods must initialise the event in a manner analogous to the
   similarly-named methods in the DOM3 Events interfaces. <a
   href="#refsDOM3EVENTS">[DOM3EVENTS]</a>

  <p>The <dfn id=data3
   title=dom-UndoManagerEvent-data><code>data</code></dfn> attribute
   represents the <a href="#undo-object">undo object</a> for the event.

  <p>The <dfn id=undo0 title=event-undo><code>undo</code></dfn> and <dfn
   id=redo title=event-redo><code>redo</code></dfn> events do not bubble,
   cannot be canceled, and have no default action. When the user agent fires
   one of these events it must use the <code><a
   href="#undomanagerevent">UndoManagerEvent</a></code> interface, with the
   <code title=dom-UndoManagerEvent-data><a href="#data3">data</a></code>
   field containing the relevant <a href="#undo-object">undo object</a>.

  <h4 id=implementation0><span class=secno>5.4.5. </span>Implementation notes</h4>

  <p>How user agents present the above conceptual model to the user is not
   defined. The undo interface could be a filtered view of the <a
   href="#undo-transaction">undo transaction history</a>, it could manipulate
   the <a href="#undo-transaction">undo transaction history</a> in ways not
   described above, and so forth. For example, it is possible to design a UA
   that appears to have separate <a href="#undo-transaction" title="undo
   transaction history">undo transaction histories</a> for each form control;
   similarly, it is possible to design systems where the user has access to
   more undo information than is present in the offical (as described above)
   <a href="#undo-transaction">undo transaction history</a> (such as
   providing a tree-based approach to document state). Such UI models should
   be based upon the single <a href="#undo-transaction">undo transaction
   history</a> described in this section, however, such that to a script
   there is no detectable difference.

  <h3 id=command><span class=secno>5.5. </span>Command APIs</h3>

  <p>The <dfn id=execCommand
   title=dom-document-execCommand><code>execCommand(<var
   title="">commandId</var>, <var title="">doShowUI</var>, <var
   title="">value</var>)</code></dfn> method on the <code><a
   href="#htmldocument">HTMLDocument</a></code> interface allows scripts to
   perform actions on the <a href="#a-selection" title="the
   selection">current selection</a> or at the current caret position.
   Generally, these commands would be used to implement editor UI, for
   example having a "delete" button on a toolbar.

  <p>There are three variants to this method, with one, two, and three
   arguments respectively. The <var title="">doShowUI</var> and <var
   title="">value</var> parameters, even if specified, are ignored unless
   otherwise stated.

  <p class=note>In this specification, in fact, the <var
   title="">doShowUI</var> parameter is always ignored, regardless of its
   value. It is included for historical reasons only.

  <p>When any of these methods are invoked, user agents must act as described
   in the list below.

  <p>For actions marked "<dfn id=editing2>editing hosts only</dfn>", if the
   selection is not entirely within an <a href="#editing1">editing host</a>,
   of if there is no selection and the caret is not inside an <a
   href="#editing1">editing host</a>, then the user agent must do nothing.

  <dl>
   <dt>If the <var title="">commandId</var> is <dfn id=undo1
    title=command-undo><code>undo</code></dfn>

   <dd>The user agent must <a href="#undo-moving0" title=do-undo>move back
    one step</a> in its <a href="#undo-transaction">undo transaction
    history</a>, restoring the associated state. If there is no further undo
    information the user agent must do nothing. See the <a
    href="#undo-history">undo history</a>.

   <dt>If the <var title="">commandId</var> is <dfn id=redo0
    title=command-redo><code>redo</code></dfn>

   <dd>The user agent must <a href="#redo-moving0" title=do-redo>move forward
    one step</a> in its <a href="#undo-transaction">undo transaction
    history</a>, restoring the associated state. If there is no further undo
    (well, "redo") information the user agent must do nothing. See the <a
    href="#undo-history">undo history</a>.

   <dt>If the <var title="">commandId</var> is <dfn id=selectall0
    title=command-selectAll><code>selectAll</code></dfn>

   <dd>The user agent must change the selection so that all the content in
    the currently focused <a href="#editing1">editing host</a> is selected.
    If no <a href="#editing1">editing host</a> is focused, then the content
    of the entire document must be selected.

   <dt>If the <var title="">commandId</var> is <dfn id=unselect
    title=command-unselect><code>unselect</code></dfn>

   <dd>
    <p>The user agent must change the selection so that nothing is selected.</p>

    <p class=big-issue>We need some sort of way in which the user can make a
     selection without risk of script clobbering it.

   <dt>If the <var title="">commandId</var> is <dfn id=superscript
    title=command-superscript><code>superscript</code></dfn>

   <dd><em><a href="#editing2">Editing hosts only.</a></em> The user agent
    must act as if the user had requested that the selection <a
    href="#contenteditable-wrapSemantic">be wrapped in the semantics</a> of
    the <code><a href="#sup">sup</a></code> element (or unwrapped, or, if
    there is no selection, have that semantic inserted or removed &mdash; the
    exact behaviour is UA-defined).

   <dt>If the <var title="">commandId</var> is <dfn id=subscript
    title=command-subscript><code>subscript</code></dfn>

   <dd><em><a href="#editing2">Editing hosts only.</a></em> The user agent
    must act as if the user had requested that the selection <a
    href="#contenteditable-wrapSemantic">be wrapped in the semantics</a> of
    the <em title=""><code><a href="#sub">sub</a></code></em> element (or,
    again, unwrapped, or have that semantic inserted or removed, as defined
    by the UA).

   <dt>If the <var title="">commandId</var> is <dfn id=formatblock
    title=command-formatBlock><code>formatBlock</code></dfn>

   <dd>
    <p><em><a href="#editing2">Editing hosts only.</a></em> This command
     changes the semantics of the blocks containing the selection.</p>

    <p>If there is no selection, then, where in the description below refers
     to the selection, the user agent must act as if the selection was an
     empty range at the caret position.</p>

    <p>If the <var title="">value</var> parameter is not specified or has a
     value other than one of the following literal strings:</p>

    <ul class=brief>
     <li><code title="">&lt;address&gt;</code>

     <li><code title="">&lt;aside&gt;</code>

     <li><code title="">&lt;h1&gt;</code>

     <li><code title="">&lt;h2&gt;</code>

     <li><code title="">&lt;h3&gt;</code>

     <li><code title="">&lt;h4&gt;</code>

     <li><code title="">&lt;h5&gt;</code>

     <li><code title="">&lt;h6&gt;</code>

     <li><code title="">&lt;nav&gt;</code>

     <li><code title="">&lt;p&gt;</code>

     <li><code title="">&lt;pre&gt;</code>
    </ul>

    <p>...then the user agent must do nothing.</p>

    <p>Otherwise, the user agent must, for every position in the selection,
     take the furthest <a href="#block-level0" title="block-level
     elements">block-level element</a> ancestor of that position that
     contains only <a href="#inline-level0">inline-level content</a> and is
     not being used as a <a href="#structured" title="structured inline-level
     elements">structured inline-level element</a>, and, if that element is a
     descendant of the editing host, rename it (as if the <code
     title="">Element.renameNode()</code> method had been used) according to
     the <var title="">value</var>, by stripping the leading
     <code>&lt;</code> character and the trailing <code>&gt;</code> character
     and using the rest as the new tag name, using the HTML namespace.

   <dt>If the <var title="">commandId</var> is <dfn id=delete
    title=command-delete><code>delete</code></dfn>

   <dd><em><a href="#editing2">Editing hosts only.</a></em> The user agent
    must act as if the user had performed <a href="#contenteditable-delete">a
    backspace operation</a>.

   <dt>If the <var title="">commandId</var> is <dfn id=forwarddelete
    title=command-forwardDelete><code>forwardDelete</code></dfn>

   <dd><em><a href="#editing2">Editing hosts only.</a></em> The user agent
    must act as if the user had performed <a href="#contenteditable-delete">a
    forward delete operation</a>.

   <dt>If the <var title="">commandId</var> is <dfn id=insertlinebreak
    title=command-insertLineBreak><code>insertLineBreak</code></dfn>

   <dd><em><a href="#editing2">Editing hosts only.</a></em> The user agent
    must act as if the user had <a href="#contenteditable-br">requested a
    line separator</a>.

   <dt>If the <var title="">commandId</var> is <dfn id=insertparagraph
    title=command-insertParagraph><code>insertParagraph</code></dfn>

   <dd><em><a href="#editing2">Editing hosts only.</a></em> The user agent
    must act as if the user had performed a <a
    href="#contenteditable-breakBlock">break block</a> editing action.

   <dt>If the <var title="">commandId</var> is <dfn id=inserttext
    title=command-insertText><code>insertText</code></dfn>

   <dd><em><a href="#editing2">Editing hosts only.</a></em> The user agent
    must act as if the user had <a
    href="#contenteditable-insertText">inserted text</a> corresponding to the
    <var title="">value</var> parameter.

   <dt>If the <var title="">commandId</var> is <code><var
    title="">vendorID</var>-<var title="">customCommandID</var></code>

   <dd>User agents may implement vendor-specific extensions to this API.
    Vendor-specific extensions to the list of commands should use the syntax
    <code><var title="">vendorID</var>-<var
    title="">customCommandID</var></code> so as to prevent clashes between
    extensions from different vendors and future additions to this
    specification.

   <dt>If the <var title="">commandId</var> is something else

   <dd>User agents must do nothing.
  </dl>

  <h3 id=selection><span class=secno>5.6. </span>The text selection APIs</h3>

  <p>Every <a href="#browsing0">browsing context</a> has <dfn id=a-selection
   title="the selection">a selection</dfn>. The selection may be empty, and
   the selection may have more than one range (a disjointed selection). The
   user should be able to change the selection. User agents are not required
   to let the user select more than one range, and may collapse multiple
   ranges in the selection to a single range when the user interacts with the
   selection. (But, of course, the user agent may let the user create
   selections with multiple ranges.)

  <p>This one selection must be shared by all the content of the browsing
   context (though not by nested <a href="#browsing0" title="browsing
   context">browsing contexts</a>), including any editing hosts in the
   document. (Editing hosts that are not inside a document cannot have a
   selection.)

  <p>If the selection is empty (collapsed, so that it has only one segment
   and that segment's start and end points are the same) then the selection's
   position should equal the caret position. When the selection is not empty,
   this specification does not define the caret position; user agents should
   follow platform conventions in deciding whether the caret is at the start
   of the selection, the end of the selection, or somewhere else.

  <p>On some platforms (such as those using Wordstar editing conventions),
   the caret position is totally independent of the start and end of the
   selection, even when the selection is empty. On such platforms, user
   agents may ignore the requirement that the cursor position be linked to
   the position of the selection altogether.

  <p>Mostly for historical reasons, in addition to the <a
   href="#browsing0">browsing context</a>'s <a href="#a-selection" title="the
   selection">selection</a>, each <code>textarea</code> and
   <code>input</code> element has an independent selection. These are the
   <dfn id=text-field title="text field selection">text field
   selections</dfn>.

  <p>The <code><a href="#datagrid0">datagrid</a></code> and
   <code>select</code> elements also have selections, indicating which items
   have been picked by the user. These are not discussed in this section.

  <p class=note>This specification does not specify how selections are
   presented to the user. The Selectors specification, in conjunction with
   CSS, can be used to style text selections using the <code><a
   href="#selection1">::selection</a></code> pseudo-element. <a
   href="#refsSELECTORS">[SELECTORS]</a> <a href="#refsCSS21">[CSS21]</a>

  <h4 id=documentSelection><span class=secno>5.6.1. </span>APIs for the
   browsing context selection</h4>

  <p>The <dfn id=getselection
   title=dom-getSelection><code>getSelection()</code></dfn> method on the
   <code><a href="#window">Window</a></code> interface must return the
   <code><a href="#selection1">Selection</a></code> object representing <a
   href="#a-selection">the selection</a> of that <code><a
   href="#window">Window</a></code> object's <a href="#browsing0">browsing
   context</a>.

  <p>For historical reasons, the <dfn id=getselection0
   title=dom-document-getSelection><code>getSelection()</code></dfn> method
   on the <code><a href="#htmldocument">HTMLDocument</a></code> interface
   must return the same <code><a href="#selection1">Selection</a></code>
   object.

  <pre class=idl>interface <dfn id=selection1>Selection</dfn> {
  readonly attribute Node <a href="#anchornode" title=dom-selection-anchorNode>anchorNode</a>;
  readonly attribute long <a href="#anchoroffset" title=dom-selection-anchorOffset>anchorOffset</a>;
  readonly attribute Node <a href="#focusnode" title=dom-selection-focusNode>focusNode</a>;
  readonly attribute long <a href="#focusoffset" title=dom-selection-focusOffset>focusOffset</a>;
  readonly attribute boolean <a href="#iscollapsed" title=dom-selection-isCollapsed>isCollapsed</a>;
  void <a href="#collapse" title=dom-selection-collapse>collapse</a>(in Node parentNode, in long offset);
  void <a href="#collapsetostart" title=dom-selection-collapseToStart>collapseToStart</a>();
  void <a href="#collapsetoend" title=dom-selection-collapseToEnd>collapseToEnd</a>();
  void <a href="#selectallchildren" title=dom-selection-selectAllChildren>selectAllChildren</a>(in Node parentNode);
  void <a href="#deletefromdocument" title=dom-selection-deleteFromDocument>deleteFromDocument</a>();
  readonly attribute long <a href="#rangecount" title=dom-selection-rangeCount>rangeCount</a>;
  Range <a href="#getrangeat" title=dom-selection-getRangeAt>getRangeAt</a>(in long index);
  void <a href="#addrange" title=dom-selection-addRange>addRange</a>(in Range range);
  void <a href="#removerange" title=dom-selection-removeRange>removeRange</a>(in Range range);
  void <a href="#removeallranges" title=dom-selection-removeAllRanges>removeAllRanges</a>();
  DOMString <a href="#tostring" title=dom-selection-toString>toString</a>();
};</pre>
  <!--
  See also:
    http://lxr.mozilla.org/mozilla/source/content/base/public/nsISelection.idl
  This spec doesn't have everything from there yet, in particular
  selectionLanguageChange() and containsNode() are missing. They are missing
  because I couldn't work out how to define them in terms of Ranges.

  I also haven't included extend():

    void <span title="dom-selection-extend">extend</span>(in Node parentNode, in long offset);
    // raise if no range
    // raise WRONG_DOCUMENT_ERR if parentNode not in document
    // do something

  ...mostly because I can't work out how to describe what it does quickly.
-->

  <p>The <code><a href="#selection1">Selection</a></code> interface is
   represents a list of <code>Range</code> objects. The first item in the
   list has index 0, and the last item has index <var title="">count</var>-1,
   where <var title="">count</var> is the number of ranges in the list. <a
   href="#refsDOM2RANGE">[DOM2RANGE]</a>

  <p>All of the members of the <code><a
   href="#selection1">Selection</a></code> interface are defined in terms of
   operations on the <code>Range</code> objects represented by this object.
   These operations can raise exceptions, as defined for the
   <code>Range</code> interface; this can therefore result in the members of
   the <code><a href="#selection1">Selection</a></code> interface raising
   exceptions as well, in addition to any explicitly called out below.</p>
  <!--- XXX example -->

  <p>The <dfn id=anchornode
   title=dom-selection-anchorNode><code>anchorNode</code></dfn> attribute
   must return the value returned by the <code title="">startContainer</code>
   attribute of the last <code>Range</code> object in the list, or null if
   the list is empty.

  <p>The <dfn id=anchoroffset
   title=dom-selection-anchorOffset><code>anchorOffset</code></dfn> attribute
   must return the value returned by the <code title="">startOffset</code>
   attribute of the last <code>Range</code> object in the list, or 0 if the
   list is empty.

  <p>The <dfn id=focusnode
   title=dom-selection-focusNode><code>focusNode</code></dfn> attribute must
   return the value returned by the <code title="">endContainer</code>
   attribute of the last <code>Range</code> object in the list, or null if
   the list is empty.

  <p>The <dfn id=focusoffset
   title=dom-selection-focusOffset><code>focusOffset</code></dfn> attribute
   must return the value returned by the <code title="">endOffset</code>
   attribute of the last <code>Range</code> object in the list, or 0 if the
   list is empty.

  <p>The <dfn id=iscollapsed
   title=dom-selection-isCollapsed><code>isCollapsed</code></dfn> attribute
   must return true if there are zero ranges, or if there is exactly one
   range and its <code title="">collapsed</code> attribute is itself true.
   Otherwise it must return false.

  <p>The <dfn id=collapse title=dom-selection-collapse><code>collapse(<var
   title="">parentNode</var>, <var title="">offset</var>)</code></dfn> method
   must raise a <code>WRONG_DOCUMENT_ERR</code> DOM exception if <var
   title="">parentNode</var>'s <code title="">ownerDocument</code> is not the
   <code><a href="#htmldocument">HTMLDocument</a></code> object with which
   the <code><a href="#selection1">Selection</a></code> object is associated.
   Otherwise it is, and the method must remove all the ranges in the <code><a
   href="#selection1">Selection</a></code> list, then create a new
   <code>Range</code> object, add it to the list, and invoke its <code
   title="">setStart()</code> and <code title="">setEnd()</code> methods with
   the <var title="">parentNode</var> and <var title="">offset</var> values
   as their arguments.

  <p>The <dfn id=collapsetostart
   title=dom-selection-collapseToStart><code>collapseToStart()</code></dfn>
   method must raise an <code>INVALID_STATE_ERR</code> DOM exception if there
   are no ranges in the list. Otherwise, it must invoke the <code
   title=dom-selection-collapse><a href="#collapse">collapse()</a></code>
   method with the <code title="">startContainer</code> and <code
   title="">startOffset</code> values of the first <code>Range</code> object
   in the list as the arguments.

  <p>The <dfn id=collapsetoend
   title=dom-selection-collapseToEnd><code>collapseToEnd()</code></dfn>
   method must raise an <code>INVALID_STATE_ERR</code> DOM exception if there
   are no ranges in the list. Otherwise, it must invoke the <code
   title=dom-selection-collapse><a href="#collapse">collapse()</a></code>
   method with the <code title="">endContainer</code> and <code
   title="">endOffset</code> values of the last <code>Range</code> object in
   the list as the arguments.

  <p>The <dfn id=selectallchildren
   title=dom-selection-selectAllChildren><code>selectAllChildren(<var
   title="">parentNode</var>)</code></dfn> method must invoke the <code
   title=dom-selection-collapse><a href="#collapse">collapse()</a></code>
   method with the <var title="">parentNode</var> value as the first argument
   and 0 as the second argument, and must then invoke the <code
   title="">selectNodeContents()</code> method on the first (and only) range
   in the list with the <var title="">parentNode</var> value as the argument.

  <p>The <dfn id=deletefromdocument
   title=dom-selection-deleteFromDocument><code>deleteFromDocument()</code></dfn>
   method must invoke the <code title="">deleteContents()</code> method on
   each range in the list, if any, from first to last.

  <p>The <dfn id=rangecount
   title=dom-selection-rangeCount><code>rangeCount</code></dfn> attribute
   must return the number of ranges in the list.

  <p>The <dfn id=getrangeat
   title=dom-selection-getRangeAt><code>getRangeAt(<var
   title="">index</var>)</code></dfn> method must return the <var
   title="">index</var>th range in the list. If <var title="">index</var> is
   less than zero or greater or equal to the value returned by the <code
   title=dom-selection-rangeCount><a href="#rangecount">rangeCount</a></code>
   attribute, then the method must raise an <code>INDEX_SIZE_ERR</code> DOM
   exception.

  <p>The <dfn id=addrange title=dom-selection-addRange><code>addRange(<var
   title="">range</var>)</code></dfn> method must add the given <var
   title="">range</var> Range object to the list of selections, at the end
   (so the newly added range is the new last range). Duplicates are not
   prevented; a range may be added more than once in which case it appears in
   the list more than once, which (for example) will cause <code
   title=dom-selection-toString><a href="#tostring">toString()</a></code> to
   return the range's text twice.</p>
  <!-- XXX how does this interact with
  deleteFromDocument() which acts on all ranges? -->

  <p>The <dfn id=removerange
   title=dom-selection-removeRange><code>removeRange(<var
   title="">range</var>)</code></dfn> method must remove the first occurrence
   of <var title="">range</var> in the list of ranges, if it appears at all.

  <p>The <dfn id=removeallranges
   title=dom-selection-removeAllRanges><code>removeAllRanges()</code></dfn>
   method must remove all the ranges from the list of ranges, such that the
   <code title=dom-selection-rangeCount><a
   href="#rangecount">rangeCount</a></code> attribute returns 0 after the
   <code title=dom-selection-removeAllRanges><a
   href="#removeallranges">removeAllRanges()</a></code> method is invoked
   (and until a new range is added to the list, either through this interface
   or via user interaction).

  <p>The <dfn id=tostring
   title=dom-selection-toString><code>toString()</code></dfn> method must
   return a concatenation of the results of invoking the <code
   title="">toString()</code> method of the <code>Range</code> object on each
   of the ranges of the selection, in the order they appear in the list
   (first to last).

  <p>In language bindings where this is supported, objects implementing the
   <code><a href="#selection1">Selection</a></code> interface must stringify
   to the value returned by the object's <code
   title=dom-selection-toString><a href="#tostring">toString()</a></code>
   method.

  <div class=example>
   <p>In the following document fragment, the emphasised parts indicate the
    selection.</p>

   <pre>&lt;p>The cute girl likes <em>the </em>&lt;cite><em>Oxford English</em> Dictionary&lt;/cite>.&lt;/p></pre>

   <p>If a script invoked <code
    title="">window.getSelection().toString()</code>, the return value would
    be "<code>the Oxford English</code>".</p>
  </div>

  <p class=note>The <code><a href="#selection1">Selection</a></code>
   interface has no relation to the <code><a
   href="#datagridselection">DataGridSelection</a></code> interface.

  <h4 id=textFieldSelection><span class=secno>5.6.2. </span>APIs for the text
   field selections</h4>

  <p class=big-issue>When we define HTMLTextAreaElement and HTMLInputElement
   we will have to add the IDL given below to both of their IDLs.

  <p>The <code>input</code> and <code>textarea</code> elements define four
   members in their DOM interfaces for handling their text selection:

  <pre
   class=idl>  void <a href="#select0" title="dom-textarea/input-select">select</a>();
           attribute unsigned long <a href="#selectionstart" title="dom-textarea/input-selectionStart">selectionStart</a>;
           attribute unsigned long <a href="#selectionend" title="dom-textarea/input-selectionEnd">selectionEnd</a>;
  void <a href="#setselectionrange" title="dom-textarea/input-setSelectionRange">setSelectionRange</a>(in unsigned long start, in unsigned long end);</pre>
  <!-- XXX also add textLength? it seems to be widely used -->

  <p>These methods and attributes expose and control the selection of
   <code>input</code> and <code>textarea</code> text fields.

  <p>The <dfn id=select0
   title="dom-textarea/input-select"><code>select()</code></dfn> method must
   cause the contents of the text field to be fully selected.

  <p>The <dfn id=selectionstart
   title="dom-textarea/input-selectionStart"><code>selectionStart</code></dfn>
   attribute must, on getting, return the offset (in logical order) to the
   character that immediately follows the start of the selection. If there is
   no selection, then it must return the offset (in logical order) to the
   character that immediately follows the text entry cursor.

  <p>On setting, it must act as if the <code
   title="dom-textarea/input-setSelectionRange"><a
   href="#setselectionrange">setSelectionRange()</a></code> method had been
   called, with the new value as the first argument, and the current value of
   the <code title="dom-textarea/input-selectionEnd"><a
   href="#selectionend">selectionEnd</a></code> attribute as the second
   argument, unless the current value of the <code
   title="dom-textarea/input-selectionEnd"><a
   href="#selectionend">selectionEnd</a></code> is less than the new value,
   in which case the second argument must also be the new value.

  <p>The <dfn id=selectionend
   title="dom-textarea/input-selectionEnd"><code>selectionEnd</code></dfn>
   attribute must, on getting, return the offset (in logical order) to the
   character that immediately follows the end of the selection. If there is
   no selection, then it must return the offset (in logical order) to the
   character that immediately follows the text entry cursor.

  <p>On setting, it must act as if the <code
   title="dom-textarea/input-setSelectionRange"><a
   href="#setselectionrange">setSelectionRange()</a></code> method had been
   called, with the current value of the <code
   title="dom-textarea/input-selectionStart"><a
   href="#selectionstart">selectionStart</a></code> attribute as the first
   argument, and new value as the second argument.

  <p>The <dfn id=setselectionrange
   title="dom-textarea/input-setSelectionRange"><code>setSelectionRange(<var
   title="">start</var>, <var title="">end</var>)</code></dfn> method must
   set the selection of the text field to the sequence of characters starting
   with the character at the <var title="">start</var>th position (in logical
   order) and ending with the character at the <span>(<var
   title="">end</var>-1)</span>th position. Arguments greater than the length
   of the value in the text field must be treated as pointing at the end of
   the text field. If <var title="">end</var> is less than or equal to <var
   title="">start</var> then the start of the selection and the end of the
   selection must both be placed immediately before the character with offset
   <var title="">end</var>. In UAs where there is no concept of an empty
   selection, this must set the cursor to be just before the character with
   offset <var title="">end</var>.

  <div class=example>
   <p>To obtain the currently selected text, the following JavaScript
    suffices:</p>

   <pre>var selectionText = control.value.substring(control.selectionStart, control.selectionEnd);</pre>

   <p>...where <var title="">control</var> is the <code>input</code> or
    <code>textarea</code> element.</p>
  </div>

  <p>Characters with no visible rendering, such as U+200D ZERO WIDTH JOINER,
   still count as characters. Thus, for instance, the selection can include
   just an invisible character, and the text insertion cursor can be placed
   to one side or another of such a character.

  <p>When these methods and attributes are used with <code>input</code>
   elements that are not displaying simple text fields, they must raise an
   <code>INVALID_STATE_ERR</code> exception.

  <h2 id=comms><span class=secno>6. </span>Communication</h2>

  <h3 id=event0><span class=secno>6.1. </span>Event definitions</h3>

  <p>Messages in <a href="#cross-document">cross-document messaging</a> and,
   by default, in <a href="#server-sent">server-sent DOM events</a>, use the
   <dfn id=message title=event-message><code>message</code></dfn> event.

  <p>The following interface is defined for this event:

  <pre class=idl>interface <dfn id=messageevent>MessageEvent</dfn> : Event {
  readonly attribute DOMString <a href="#data4" title=dom-MessageEvent-data>data</a>;
  readonly attribute DOMString <a href="#domain2" title=dom-MessageEvent-domain>domain</a>;
  readonly attribute DOMString <a href="#uri" title=dom-MessageEvent-uri>uri</a>;
  readonly attribute Document <a href="#source1" title=dom-MessageEvent-source>source</a>;
  void <a href="#initmessageevent" title=dom-MessageEvent-initMessageEvent>initMessageEvent</a>(in DOMString typeArg, in boolean canBubbleArg, in boolean cancelableArg, in DOMString dataArg, in DOMString domainArg, in DOMString uriArg, in Document documentArg);
  void <a href="#initmessageeventns" title=dom-MessageEvent-initMessageEventNS>initMessageEventNS</a>(in DOMString namespaceURI, in DOMString typeArg, in boolean canBubbleArg, in boolean cancelableArg, in DOMString dataArg, in DOMString domainArg, in DOMString uriArg, in Document documentArg);
};</pre>

  <p>The <dfn id=initmessageevent
   title=dom-MessageEvent-initMessageEvent><code>initMessageEvent()</code></dfn>
   and <dfn id=initmessageeventns
   title=dom-MessageEvent-initMessageEventNS><code>initMessageEventNS()</code></dfn>
   methods must initialise the event in a manner analogous to the
   similarly-named methods in the DOM3 Events interfaces. <a
   href="#refsDOM3EVENTS">[DOM3EVENTS]</a>

  <p>The <dfn id=data4 title=dom-MessageEvent-data><code>data</code></dfn>
   attribute represents the message being sent.

  <p>The <dfn id=domain2
   title=dom-MessageEvent-domain><code>domain</code></dfn> attribute
   represents, in <a href="#cross-document">cross-document messaging</a>, the
   domain of the document from which the message came.

  <p>The <dfn id=uri title=dom-MessageEvent-uri><code>uri</code></dfn>
   attribute represents, in <a href="#cross-document">cross-document
   messaging</a>, the address of the document from which the message came.

  <p>The <dfn id=source1
   title=dom-MessageEvent-source><code>source</code></dfn> attribute
   represents, in <a href="#cross-document">cross-document messaging</a>, the
   <code>Document</code> from which the message came.

  <h3 id=server-sent-events><span class=secno>6.2. </span><dfn
   id=server-sent>Server-sent DOM events</dfn></h3>
  <!-- event-source -->

  <p>This section describes a mechanism for allowing servers to dispatch DOM
   events into documents that expect it. The <code><a
   href="#event-source">event-source</a></code> element provides a simple
   interface to this mechanism.

  <h4 id=the-remoteeventtarget><span class=secno>6.2.1. </span>The <dfn
   id=remoteeventtarget><code>RemoteEventTarget</code></dfn> interface</h4>

  <p>Any object that implements the <code>EventTarget</code> interface must
   also implement the <code><a
   href="#remoteeventtarget0">RemoteEventTarget</a></code> interface.

  <pre
   class=idl>interface <dfn id=remoteeventtarget0>RemoteEventTarget</dfn> {
  void <a href="#addeventsource" title=dom-RemoteEventTarget-addEventSource>addEventSource</a>(in DOMString src);
  void <a href="#removeeventsource" title=dom-RemoteEventTarget-removeEventSource>removeEventSource</a>(in DOMString src);
};</pre>

  <p>When the <dfn id=addeventsource
   title=dom-RemoteEventTarget-addEventSource><code>addEventSource(<var
   title="">src</var>)</code></dfn> method is invoked, the user agent must
   add the URI specified in <var title="">src</var> to the <a
   href="#list-of3" title=concept-event-source-list>list of event sources</a>
   for that object. The same URI can be registered multiple times.

  <p>When the <dfn id=removeeventsource
   title=dom-RemoteEventTarget-removeEventSource><code>removeEventSource(<var
   title="">src</var>)</code></dfn> method is invoked, the user agent must
   remove the URI specified in <var title="">src</var> from the <a
   href="#list-of3" title=concept-event-source-list>list of event sources</a>
   for that object. If the same URI has been registered multiple times,
   removing it must only remove one instance of that URI for each invocation
   of the <code title=removeEventSource>removeEventSource()</code> method.

  <p>Relative URIs must be resolved relative to <span
   class=big-issue>...</span>.

  <h4 id=connecting><span class=secno>6.2.2. </span>Connecting to an event
   stream</h4>

  <p>Each object implementing the <code>EventTarget</code> and <code><a
   href="#remoteeventtarget0">RemoteEventTarget</a></code> interfaces has a
   <dfn id=list-of3 title=concept-event-source-list>list of event
   sources</dfn> that are registered for that object.

  <p>When a new URI is added to this list, the user agent should, as soon as
   all currently executing scripts (if any) have finished executing, and if
   the specified URI isn't removed from the list before they do so, fetch the
   resource identified by that URI.

  <p>When an event source is removed from the list of event sources for an
   object, if that resource is still being fetched, then the relevant
   connection must be closed.

  <p>Since connections established to remote servers for such resources are
   expected to be long-lived, UAs should ensure that appropriate buffering is
   used. In particular, while line buffering may be safe if lines are defined
   to end with a single U+000A LINE FEED character, block buffering or line
   buffering with different expected line endings can cause delays in event
   dispatch.

  <p>In general, the semantics of the transport protocol specified by the
   URIs for the event sources must be followed, including HTTP caching rules.

  <p>For HTTP connections, the <code title="">Accept</code> header may be
   included; if included, it must only contain formats of event framing that
   are supported by the user agent (one of which must be
   <code>application/x-dom-event-stream</code>, as described below).

  <p>Other formats of event framing may also be supported in addition to
   <code>application/x-dom-event-stream</code>, but this specification does
   not define how they are to be parsed or processed.

  <p class=note>Such formats could include systems like SMS-push; for example
   servers could use <code title="">Accept</code> headers and HTTP redirects
   to an SMS-push mechanism as a kind of protocol negotiation to reduce
   network load in GSM environments.

  <p>User agents should use the <code>Cache-Control: no-cache</code> header
   in requests to bypass any caches for requests of event sources.

  <p>For connections to domains other than the <a href="#domain0">document's
   domain</a>, the semantics of the Access-Control HTTP header must be
   followed. <a href="#refsACCESSCONTROL">[ACCESSCONTROL]</a>

  <p>HTTP 200 OK responses with a <a href="#content-type8">Content-Type</a>
   header specifying the type <code>application/x-dom-event-stream</code>
   that are either from the <a href="#domain0">document's domain</a> or
   explicitly allowed by the Access-Control HTTP headers must be processed
   line by line <a href="#event-stream-interpretation">as described
   below</a>.

  <p>For the purposes of such successfully opened event streams only, user
   agents should ignore HTTP cache headers, and instead assume that the
   resource indicates that it does not wish to be cached.

  <p>If such a resource completes loading (i.e. the entire HTTP response body
   is received or the connection itself closes), the user agent should
   request the event source resource again after a delay of approximately
   five seconds.

  <p>HTTP 200 OK responses that have a <a
   href="#content-type8">Content-Type</a> other than
   <code>application/x-dom-event-stream</code> (or some other supported
   type), and HTTP responses whose Access-Control headers indicate that the
   resource are not to be used, must be ignored and must prevent the user
   agent from refetching the resource for that event source.

  <p>HTTP 201 Created, 202 Accepted, 203 Non-Authoritative Information, and
   206 Partial Content responses must be treated like HTTP 200 OK responses
   for the purposes of reopening event source resources. They are, however,
   likely to indicate an error has occurred somewhere and may cause the user
   agent to emit a warning.

  <p>HTTP 204 No Content, and 205 Reset Content responses must be treated as
   if they were 200 OK responses with the right MIME type but no content, and
   should therefore cause the user agent to refetch the resource after a
   short delay.

  <p>HTTP 300 Multiple Choices responses should be handled automatically if
   possible (treating the responses as if they were 302 Found responses
   pointing to the appropriate resource), and otherwise must be treated as
   HTTP 404 responses.

  <p>HTTP 301 Moved Permanently responses must cause the user agent to
   reconnect using the new server specified URI instead of the previously
   specified URI for all subsequent requests for this event source. (It
   doesn't affect other event sources with the same URI unless they also
   receive 301 responses, and it doesn't affect future sessions, e.g. if the
   page is reloaded.)

  <p>HTTP 302 Found, 303 See Other, and 307 Temporary Redirect responses must
   cause the user agent to connect to the new server-specified URI, but if
   the user agent needs to again request the resource at a later point, it
   must return to the previously specified URI for this event source.

  <p>HTTP 304 Not Modified responses should be handled like HTTP 200 OK
   responses, with the content coming from the user agent cache. A new
   request should then be made after a short delay of approximately five
   seconds.

  <p>HTTP 305 Use Proxy, HTTP 401 Unauthorized, and 407 Proxy Authentication
   Required should be treated transparently as for any other subresource.

  <p>Any other HTTP response code not listed here should cause the user agent
   to stop trying to process this event source.</p>
  <!--
  including: HTTP 400 Bad Request, 403 Forbidden, 404 Not Found, 405
  Method Not Allowed, 406 Not Acceptable, 408 Request Timeout, 409
  Conflict, 410 Gone, 411 Length Required, 412 Precondition Failed,
  413 Request Entity Too Large, 414 Request-URI Too Long, 415
  Unsupported Media Type, 416 Requested Range Not Satisfiable, 417
  Expectation Failed, 500 Internal Server Error, 501 Not Implemented,
  502 Bad Gateway, 503 Service Unavailable, 504 Gateway Timeout, and
  505 HTTP Version Not Supported responses -->

  <p>DNS errors must be considered fatal, and cause the user agent to not
   open any connection for that event source.

  <p>For non-HTTP protocols, UAs should act in equivalent ways.

  <h4 id=parsing0><span class=secno>6.2.3. </span>Parsing an event stream</h4>

  <p>This event stream format's MIME type is
   <code>application/x-dom-event-stream</code>.

  <p>The event stream format is (in pseudo-BNF):

  <pre>&lt;stream&gt;          ::= &lt;bom&gt;? &lt;event&gt;*
&lt;event&gt;           ::= [ &lt;comment&gt; | &lt;command&gt; | &lt;field&gt; ]* &lt;newline&gt;
&lt;comment&gt;         ::= ';' &lt;any-char&gt;* &lt;newline&gt;
&lt;command&gt;         ::= ':' &lt;any-char&gt;* &lt;newline&gt;
&lt;field&gt;           ::= &lt;name&gt; [ ':' &lt;space&gt;? &lt;any-char&gt;* ]? &lt;newline&gt;
&lt;name&gt;            ::= &lt;name-start-char&gt; &lt;name-char&gt;*

# characters:
&lt;bom&gt;             ::= a single U+FEFF BYTE ORDER MARK character
&lt;space&gt;           ::= a single U+0020 SPACE character (' ')
&lt;newline&gt;         ::= a U+000D CARRIAGE RETURN character
                      followed by a U+000A LINE FEED character
                      | a single U+000D CARRIAGE RETURN character
                      | a single U+000A LINE FEED character
                      | the end of the file
&lt;name-start-char&gt; ::= a single Unicode character other than
                      ':', ';', U+000D CARRIAGE RETURN and U+000A LINE FEED
&lt;name-char&gt;       ::= a single Unicode character other than
                      ':', U+000D CARRIAGE RETURN and U+000A LINE FEED
&lt;any-char&gt;        ::= a single Unicode character other than
                      U+000D CARRIAGE RETURN and U+000A LINE FEED
</pre>

  <p>Event streams in this format must always be encoded as UTF-8. Lines must
   be separated by either a U+000D CARRIAGE RETURN U+000A LINE FEED (CRLF)
   character pair, a single U+000A LINE FEED (LF) character, or a single
   U+000D CARRIAGE RETURN (CR) character. User agents must treat those three
   variants as equivalent line terminators.

  <p>Bytes that are not valid UTF-8 sequences must be interpreted as the
   U+FFFD REPLACEMENT CHARACTER.

  <p>A leading U+FEFF BYTE ORDER MARK character must be ignored if present.

  <p>The stream must then be parsed by reading everything line by line, in
   blocks separated by blank lines. Comment lines (those starting with the
   character ';') and command lines (those starting with the character ':')
   must be ignored.

  <p>Command lines are reserved for future extensions.</p>
  <!--XXX Lachlan says:
    For the next version of server sent events, it might be useful if
    authors could specify the retry interval for connections.

    e.g. In cases where it is known that content is only updated at
    specified intervals (e.g. once per minute), having the browser retry
    the connection every 5 seconds and fire the event with the same
    content may be excessive.

    This could possibly be done using the :command syntax.

    e.g.
      Event: click
      :retry 60000

    The browser would then retry the connection in 60,000 milliseconds (1
    minute).
  -->

  <p>For each non-blank, non-comment, non-command line, the field name must
   first be taken. This is everything on the line up to but not including the
   first colon (':') or the line terminator, whichever comes first. Then, if
   there was a colon, the data for that line must be taken. This is
   everything after the colon, ignoring a single space after the colon if
   there is one, up to the end of the line. If there was no colon the data is
   the empty string.

  <div class=example>
   <p>Examples:</p>

   <pre>Field name:&nbsp;Field data</pre>

   <pre>This is a blank field</pre>

   <pre>1. These two lines:&nbsp;have the same data
2. These two lines:have the same data</pre>

   <pre>1. But these two lines:&nbsp; do not
2. But these two lines:&nbsp;do not</pre>
  </div>

  <p>If a field name occurs multiple times in a block, the value for that
   field in that black must consist of the data parts for each of those
   lines, concatenated with U+000A LINE FEED characters between them
   (regardless of what the line terminators used in the stream actually are).

  <div class=example>
   <p>For example, the following block:</p>

   <pre>Test:&nbsp;Line 1
Foo:&nbsp;&nbsp;Bar
Test:&nbsp;Line 2</pre>

   <p>...is treated as having two fields, one called <code>Test</code> with
    the value "<code>Line 1\nLine 2</code>" (where <code>\n</code> represents
    a newline), and one called <code>Foo</code> with the value
    "<code>&nbsp;Bar</code>" (note the leading space character).</p>
  </div>

  <p>A block thus consists of all the name-value pairs for its fields.
   Command lines have no effect on blocks and are not considered part of a
   block.

  <p class=note>Since any random stream of characters matches the above
   format, there is no need to define any error handling.

  <h4 id=event-stream-interpretation><span class=secno>6.2.4.
   </span>Interpreting an event stream</h4>

  <p>Once the fields have been parsed, they are interpreted as follows (these
   are case-sensitive exact comparisons):

  <dl>
   <dt><code title="">Event</code> field

   <dd>
    <p>This field gives the name of the event. For example, <code
     title="">load</code>, <code title="">DOMActivate</code>, <code
     title="">updateTicker</code>. If there is no field with this name, the
     name <code title=event-message><a href="#message">message</a></code>
     must be used.

   <dt><code title="">Namespace</code> field

   <dd>
    <p>This field gives the DOM3 namespace for the event. (For normal DOM
     events this would be null.) If it isn't specified the event namespace is
     null.

   <dt><code title="">Class</code> field

   <dd>
    <p>This field gives is the interface used for the event, for instance
     <code>Event</code>, <code>UIEvent</code>, <code>MutationEvent</code>,
     <code>KeyboardEvent</code>, etc. For compatibility with DOM3 Events, the
     values <code title="">UIEvents</code>, <code
     title="">MouseEvents</code>, <code title="">MutationEvents</code>, and
     <code title="">HTMLEvents</code> are valid values and must be treated
     respectively as meaning the interfaces <code>UIEvent</code>,
     <code>MouseEvent</code>, <code>MutationEvent</code>, and
     <code>Event</code>. (This value can therefore be used as the argument to
     <code title="">createEvent()</code>.)</p>

    <p>If the value is not specified but the <code title="">Namespace</code>
     is null and the <code title="">Event</code> field exactly matches one of
     the events specified by DOM3 Events in <a
     href="http://www.w3.org/TR/DOM-Level-3-Events/events.html#Events-EventTypes-complete">section
     1.4.2 "Complete list of event types"</a>, then the interface used must
     default to the interface relevant for that event type. <a
     href="#refsDOM3EVENTS">[DOM3EVENTS]</a></p>

    <div class=example>
     <p>For example:</p>

     <pre>Event: click</pre>

     <p>...would cause <code title="">Class</code> to be treated as
      <code>MouseEvent</code>.</p>
    </div>

    <p>If the <code title="">Namespace</code> is null and the <code
     title="">Event</code> field is <code title=event-message><a
     href="#message">message</a></code> (including if it was not specified
     explicitly), then the <code><a
     href="#messageevent">MessageEvent</a></code> interface must be used.</p>

    <p>Otherwise, the <code>Event</code> interface must be used.</p>

    <p>It is quite possible to give the wrong class for an event. This is
     equivalent to creating an event in the DOM using the DOM Event APIs, but
     using the wrong interface for it.</p>

   <dt><code title="">Bubbles</code> field

   <dd>
    <p>This field specifies whether the event is to bubble. If it is
     specified and has the value <code title="">No</code>, the event must not
     bubble. If it is specified and has any other value (including <code
     title="">no</code> or <code title="">NO</code>) then the event must
     bubble.</p>

    <p>If it is not specified but the <code title="">Namespace</code> field
     is null and the <code title="">Event</code> field exactly matches one of
     the events specified by DOM3 Events in <a
     href="http://www.w3.org/TR/DOM-Level-3-Events/events.html#Events-EventTypes-complete">section
     1.4.2 "Complete list of event types"</a>, then the event must bubble if
     the DOM3 Events spec specifies that that event bubbles, and musn't
     bubble if it specifies it does not. <a
     href="#refsDOM3EVENTS">[DOM3EVENTS]</a></p>

    <div class=example>
     <p>For example:</p>

     <pre>Event: load</pre>

     <p>...would cause <code title="">Bubbles</code> to be treated as <code
      title="">No</code>.</p>
    </div>

    <p>Otherwise, the event must bubble.</p>

   <dt><code title="">Cancelable</code> field

   <dd>
    <p>This field specifies whether the event can have its default action
     prevented. If it is specified and has the value <code
     title="">No</code>, the event must not be cancelable. If it is specified
     and has any other value (including <code title="">no</code> or <code
     title="">NO</code>) then the event must be cancelable.</p>

    <p>If it is not specified, but the <code title="">Namespace</code> field
     is null and the <code title="">Event</code> field exactly matches one of
     the events specified by DOM3 Events in <a
     href="http://www.w3.org/TR/DOM-Level-3-Events/events.html#Events-EventTypes-complete">section
     1.4.2 "Complete list of event types"</a>, then the event must be
     cancelable if the DOM3 Events specification specifies that it is, and
     must not be cancelable otherwise. <a
     href="#refsDOM3EVENTS">[DOM3EVENTS]</a></p>

    <div class=example>
     <p>For example:</p>

     <pre>Event: load</pre>

     <p>...would cause <code title="">Cancelable</code> to be treated as
      <code title="">No</code>.</p>
    </div>

    <p>Otherwise, the event must be cancelable.</p>

   <dt><code title="">Target</code> field

   <dd>
    <p>This field gives the node that the event is to be dispatched on.</p>

    <p>If the object for which the event source is being processed is not a
     Node, but the <code title="">Target</code> field is nonetheless
     specified, then the event must be dropped.</p>

    <p>Otherwise, if field is specified and its value starts with a <code
     title="">#</code> character, then the remainder of the value represents
     an ID, and the event must be dispatched on the same node as would be
     obtained by the <code title="">getElementById()</code> method on the
     <code title="">ownerDocument</code> of the node whose event source is
     being processed.</p>

    <div class=example>
     <p>For example,</p>

     <pre>Target: #test</pre>

     <p>...would target the element with ID <code title="">test</code>.</p>
    </div>

    <p>Otherwise, if the field is specified and its value is the literal
     string "<code title="">Document</code>", then the event must be
     dispatched at the <code title="">ownerDocument</code> of the node whose
     event source is being processed.</p>

    <p>Otherwise, the field (whether specified or not) is ignored and the
     event must be dispatched at the object itself.</p>
  </dl>

  <p>Other fields depend on the interface specified (or possibly implied) by
   the <code title="">Class</code> field. If the specified interface has an
   attribute that exactly matches the name of the field, and the value of the
   field can be converted (using the type conversions defined in ECMAScript)
   to the type of the attribute, then it must be used. Any attributes (other
   than the <code>Event</code> interface attributes) that do not have
   matching fields are initialised to zero, null, false, or the empty string.

  <div class=example>
   <p>For example:</p>

   <pre>Event: click
Class: MouseEvent
button: 2</pre>

   <p>...would result in a 'click' event using the <code>MouseEvent</code>
    interface that has <code>button</code> set to <code title="">2</code> but
    <code>screenX</code>, <code>screenY</code>, etc, set to 0, false, or null
    as appropriate.</p>
  </div>

  <p>If a field does not match any of the attributes on the event, it must be
   ignored.

  <div class=example>
   <p>For example:</p>

   <pre>Event: keypress
Class: MouseEvent
keyIdentifier: 0</pre>

   <p>...would result in a <code>MouseEvent</code> event with its fields all
    at their default values, with the event name being <code
    title="">keypress</code>. The <code title="">keyIdentifier</code> field
    would be ignored. (If the author had not included the <code
    title="">Class</code> field explicitly, it would have just worked, since
    the class would have defaulted as described above.)</p>
  </div>

  <p>Once a blank line or the end of the file is reached, an event of the
   type and namespace given by the <code title="">Event</code> and
   <code>Namespace</code> fields respectively must be synthesized and
   dispatched to the appropriate node as described by the fields above. No
   event must be dispatched until a blank line has been received or the end
   of the file reached.

  <p>The event must be dispatched as if using the DOM <code
   title="">dispatchEvent()</code> method. Thus, if the <code
   title="">Event</code> field was omitted, leaving the name as the empty
   string, or if the name had invalid characters, then the dispatching of the
   event fails.

  <p>Events fired from event sources do not have user-agent default actions.

  <div class=example>
   <p>The following event stream, once followed by a blank line:</p>

   <pre>data: YHOO
data: -2
data: 10</pre>

   <p>...would cause an event <code title=event-message><a
    href="#message">message</a></code> with the interface <code><a
    href="#messageevent">MessageEvent</a></code> to be dispatched on the
    <code><a href="#event-source">event-source</a></code> element, which
    would then bubble up the DOM, and whose <code
    title=dom-MessageEvent-data><a href="#data4">data</a></code> attribute
    would contain the string <code>YHOO\n-2\n10</code> (where <code>\n</code>
    again represents a newline).</p>

   <p>This could be used as follows:

   <pre>&lt;event-source src="http://stocks.example.com/ticker.php"
              onmessage="var data = event.data.split('\n'); updateStocks(data[0], data[1], data[2]);"&gt;</pre>

   <p>...where <code title="">updateStocks()</code> is a function defined as:</p>

   <pre>function updateStocks(symbol, delta, value) { ... }</pre>

   <p>...or some such.</p>
  </div>

  <div class=example>
   <p>The following stream contains four blocks and therefore fires four
    events. The first block has just a comment, and will fire a <code
    title=event-message><a href="#message">message</a></code> event with all
    the fields set to the empty string or null. The second block has two
    fields with names "load" and "Target" respectively; since there is no
    "<code title="">load</code>" member on the <code><a
    href="#messageevent">MessageEvent</a></code> object that field is
    ignored, leaving the event as a second <code title=event-message><a
    href="#message">message</a></code> event with all the fields set to the
    empty string or null, but this time the event is targetted at an element
    with ID "image1". The third block is empty (no lines between two blank
    lines), and the fourth block has only two comments, so they both yet
    again fire <code title=event-message><a
    href="#message">message</a></code> events with all the fields set to the
    empty string or null.</p>

   <pre>; test

load
Target: #image1


; if any more events follow this block, they will not be affected by
; the "Target" and "load" fields above.
</pre>
  </div>

  <h4 id=notes><span class=secno>6.2.5. </span>Notes</h4>

  <p>Legacy proxy servers are known to, in certain cases, drop HTTP
   connections after a short timeout. To protect against such proxy servers,
   authors can include a comment line (one starting with a ';' character)
   every 15 seconds or so.

  <p>Authors wishing to relate event source connections to each other or to
   specific documents previously served might find that relying on IP
   addresses doesn't work, as individual clients can have multiple IP
   addresses (due to having multiple proxy servers) and individual IP
   addresses can have multiple clients (due to sharing a proxy server). It is
   better to include a unique identifier in the document when it is served
   and then pass that identifier as part of the URI in the <code
   title=attr-event-source-src><a href="#src11">src</a></code> attribute of
   the <code><a href="#event-source">event-source</a></code> element.

  <p>Implementations that support HTTP's per-server connection limitation
   might run into trouble when opening multiple pages from a site if each
   page has an <code><a href="#event-source">event-source</a></code> to the
   same domain. Authors can avoid this using the relatively complex mechanism
   of using unique domain names per connection, or by allowing the user to
   enable or disable the <code><a
   href="#event-source">event-source</a></code> functionality on a per-page
   basis.

  <h3 id=network><span class=secno>6.3. </span>Network connections</h3>

  <p>To enable Web applications to communicate with each other in local area
   networks, and to maintain bidirectional communications with their
   originating server, this specification introduces the <code><a
   href="#connection0">Connection</a></code> interface.

  <p>The <code><a href="#window">Window</a></code> interface provides three
   constructors for creating <code><a
   href="#connection0">Connection</a></code> objects: <code
   title=dom-TCPConnection><a
   href="#tcpconnection">TCPConnection()</a></code>, for creating a direct
   (possibly encrypted) link to another node on the Internet using TCP/IP;
   <code title=dom-LocalBroadcastConnection><a
   href="#localbroadcastconnection">LocalBroadcastConnection()</a></code>,
   for creating a connection to any listening peer on a local network (which
   could be a local TCP/IP subnet using UDP, a Bluetooth PAN, or another kind
   of network infrastructure); and <code title=dom-PeerToPeerConnection><a
   href="#peertopeerconnection">PeerToPeerConnection()</a></code>, for a
   direct peer-to-peer connection (which could again be over TCP/IP,
   Bluetooth, IrDA, or some other type of network).

  <p class=note>This interface does not allow for raw access to the
   underlying network. For example, this interface could not be used to
   implement an IRC client without proxying messages through a custom server.

  <h4 id=network-intro><span class=secno>6.3.1. </span>Introduction</h4>

  <p><em>This section is non-normative.</em>

  <p class=big-issue>An introduction to the client-side and server-side of
   using the direct connection APIs.

  <p class=big-issue>An example of a party-line implementation of a broadcast
   service, and direct peer-to-peer chat for direct local connections.</p>
  <!--
    <div class="example">
     <p>The following script creates a connection to a local party
     line:</p>
     <pre>var a = new LocalBroadcastConnection();
  a.onread = function(e) { alert(e.source + ' wrote ' + e.data); }
  a.send('hello');</pre>
    </div>
-->
  <!--XXX
   Explain why we don't use HTTP instead of our own protocol: wouldn't
   work for peer-to-peer, too much work to implement server if you
   have to implement a compliant HTTP server as well, etc
  -->

  <h4 id=the-connection><span class=secno>6.3.2. </span>The <code><a
   href="#connection0">Connection</a></code> interface</h4>

  <pre class=idl>interface <dfn id=connection0>Connection</dfn> {
  readonly attribute DOMString <a href="#network1" title=dom-Connection-network>network</a>;
  readonly attribute DOMString <a href="#peer" title=dom-Connection-peer>peer</a>;
  readonly attribute int <a href="#readystate0" title=dom-Connection-readyState>readyState</a>;
           attribute EventListener <a href="#onopen" title=dom-Connection-onopen>onopen</a>;
           attribute EventListener <a href="#onread" title=dom-Connection-onread>onread</a>;
           attribute EventListener <a href="#onclose" title=dom-Connection-onclose>onclose</a>;
  void <a href="#send" title=dom-Connection-send>send</a>(in DOMString data);
  void <a href="#disconnect" title=dom-Connection-disconnect>disconnect</a>();
};</pre>

  <p><code><a href="#connection0">Connection</a></code> objects must also
   implement the <code>EventTarget</code> interface. <a
   href="#refsDOM3EVENTS">[DOM3EVENTS]</a>

  <p>When a <code><a href="#connection0">Connection</a></code> object is
   created, the UA must try to establish a connection, as described in the
   sections below describing each connection type.

  <p>The <dfn id=network1
   title=dom-Connection-network><code>network</code></dfn> attribute
   represents the name of the network connection (the value depends on the
   kind of connection being established). The <dfn id=peer
   title=dom-Connection-peer><code>peer</code></dfn> attribute identifies the
   remote host for direct (non-broadcast) connections.

  <p>The <code title=dom-Connection-network><a
   href="#network1">network</a></code> attribute must be set as soon as the
   <code><a href="#connection0">Connection</a></code> object is created, and
   keeps the same value for the lifetime of the object. The <code
   title=dom-Connection-peer><a href="#peer">peer</a></code> attribute must
   initially be set to the empty string and must be updated once, when the
   connection is established, after which point it must keep the same value
   for the lifetime of the object.

  <p>The <dfn id=readystate0
   title=dom-Connection-readyState><code>readyState</code></dfn> attribute
   represents the state of the connection. When the object is created it must
   be set to 0. It can have the following values:

  <dl>
   <dt>0 Connecting

   <dd>The connection has not yet been established.

   <dt>1 Connected

   <dd>The connection is established and communication is possible.

   <dt>2 Closed

   <dd>The connection has been closed.
  </dl>

  <p id=openConnection>Once a connection is established, the <code
   title=dom-Connection-readyState><a
   href="#readystate0">readyState</a></code> attribute's value must be
   changed to 1, and the <code title=event-connection-open><a
   href="#open3">open</a></code> event must be fired on the <code><a
   href="#connection0">Connection</a></code> object.

  <p>When data is received, the <code title=event-connection-read><a
   href="#read">read</a></code> event will be fired on the <code><a
   href="#connection0">Connection</a></code> object.</p>
  <!-- conf crit for this
  statement is in the various protocol-specific sections below. -->

  <p id=closeConnection>When the connection is closed, the <code
   title=dom-Connection-readyState><a
   href="#readystate0">readyState</a></code> attribute's value must be
   changed to 2, and the <code title=event-connection-close><a
   href="#close0">close</a></code> event must be fired on the <code><a
   href="#connection0">Connection</a></code> object.

  <p>The <dfn id=onopen
   title=dom-Connection-onopen><code>onopen</code></dfn>, <dfn id=onread
   title=dom-Connection-onread><code>onread</code></dfn>, and <dfn id=onclose
   title=dom-Connection-onclose><code>onclose</code></dfn> attributes must,
   when set, register their new value as an event listener for their
   respective events (namely <code title=event-connection-open><a
   href="#open3">open</a></code>, <code title=event-connection-read><a
   href="#read">read</a></code>, and <code title=event-connection-close><a
   href="#close0">close</a></code>), and unregister their previous value if
   any.

  <p>The <dfn id=send title=dom-Connection-send><code>send()</code></dfn>
   method transmits data using the connection. If the connection is not yet
   established, it must raise an <code>INVALID_STATE_ERR</code> exception. If
   the connection <em>is</em> established, then the behaviour depends on the
   connection type, as described below.

  <p>The <dfn id=disconnect
   title=dom-Connection-disconnect><code>disconnect()</code></dfn> method
   must close the connection, if it is open. If the connection is already
   closed, it must do nothing. Closing the connection causes a <code
   title=event-connection-close><a href="#close0">close</a></code> event to
   be fired and the <code title=dom-Connection-readyState><a
   href="#readystate0">readyState</a></code> attribute's value to change, as
   <a href="#closeConnection">described above</a>.

  <h4 id=connection><span class=secno>6.3.3. </span>Connection Events</h4>

  <p>All the events described in this section are events in no namespace,
   which do not bubble, are not cancelable, and have no default action.

  <p>The <dfn id=open3 title=event-connection-open><code>open</code></dfn>
   event is fired when the connection is established. UAs must use the normal
   <code>Event</code> interface when firing this event.

  <p>The <dfn id=close0 title=event-connection-close><code>close</code></dfn>
   event is fired when the connection is closed (whether by the author,
   calling the <code title=dom-Connection-disconnect><a
   href="#disconnect">disconnect()</a></code> method, or by the server, or by
   a network error). UAs must use the normal <code>Event</code> interface
   when firing this event as well.

  <p class=note>No information regarding why the connection was closed is
   passed to the application in this version of this specification.

  <p>The <dfn id=read title=event-connection-read><code>read</code></dfn>
   event is fired when when data is received for a connection. UAs must use
   the <code><a href="#connectionreadevent">ConnectionReadEvent</a></code>
   interface for this event.

  <pre
   class=idl>interface <dfn id=connectionreadevent>ConnectionReadEvent</dfn> : Event {
  readonly attribute DOMString <a href="#data5" title=dom-ConnectionReadEvent-data>data</a>;
  readonly attribute DOMString <a href="#source2" title=dom-ConnectionReadEvent-source>source</a>;
  void <a href="#initconnectionreadevent" title=dom-ConnectionReadEvent-initConnectionReadEvent>initConnectionReadEvent</a>(in DOMString typeArg, in boolean canBubbleArg, in boolean cancelableArg, in DOMString dataArg);
  void <a href="#initconnectionreadeventns" title=dom-ConnectionReadEvent-initConnectionReadEventNS>initConnectionReadEventNS</a>(in DOMString namespaceURI, in DOMString typeArg, in boolean canBubbleArg, in boolean cancelableArg, in DOMString dataArg);
};
</pre>

  <p>The <dfn id=initconnectionreadevent
   title=dom-ConnectionReadEvent-initConnectionReadEvent><code>initConnectionReadEvent()</code></dfn>
   and <dfn id=initconnectionreadeventns
   title=dom-ConnectionReadEvent-initConnectionReadEventNS><code>initConnectionReadEventNS()</code></dfn>
   methods must initialise the event in a manner analogous to the
   similarly-named methods in the DOM3 Events interfaces. <a
   href="#refsDOM3EVENTS">[DOM3EVENTS]</a>

  <p>The <dfn id=data5
   title=dom-ConnectionReadEvent-data><code>data</code></dfn> attribute
   represents the data that was transmitted from the peer.

  <p>The <dfn id=source2
   title=dom-ConnectionReadEvent-source><code>source</code></dfn> attribute
   represents the name of the peer. This is primarily useful on broadcast
   connections; on direct connections it is equal to the <code
   title=dom-Connection-peer><a href="#peer">peer</a></code> attribute on the
   <code><a href="#connection0">Connection</a></code> object.</p>
  <!-- XXX check that the following three sections define "the data
  that was transmitted" and "the name of the peer" in terms that mean
  they fit into the above definitions ("for the purposes of the
  ConnectionReadEvent"), and check they say that they MUST be set
  correctly. -->
  <!-- XXX should we have a Connection attribute on the event? -->

  <p>Events that would be fired during script execution (e.g. between the
   connection object being created &mdash; and thus the connection being
   established &mdash; and the current script completing; or, during the
   execution of a <code title=event-connection-read><a
   href="#read">read</a></code> event handler) must be buffered, and those
   events queued up and each one individually fired after the script has
   completed.</p>
  <!-- XXX make this more generic -->

  <h4 id=tcp-connections><span class=secno>6.3.4. </span>TCP connections</h4>

  <p>The <dfn id=tcpconnection
   title=dom-TCPConnection><code>TCPConnection(<var title="">subdomain</var>,
   <var title="">port</var>, <var title="">secure</var>)</code></dfn>
   constructor on the <code><a href="#window">Window</a></code> interface
   returns a new object implementing the <code><a
   href="#connection0">Connection</a></code> interface, set up for a direct
   connection to a specified host on the page's domain.

  <p>When this constructor is invoked, the following steps must be followed.

  <p>First, if the domain part of the script's <a href="#origin0">origin</a>
   is not a host name (e.g. it is an IP address) then the UA must raise a <a
   href="#security8">security exception</a>. <span class=issue>We currently
   don't allow connections to be set up back to an originating IP address,
   but we could, if the subdomain is the empty string.</span>

  <p>Then, if the <var title="">subdomain</var> argument is null or the empty
   string, the target host is the domain part of the script's <a
   href="#origin0">origin</a>. Otherwise, the <var title="">subdomain</var>
   argument is prepended to the domain part of the script's origin with a dot
   separating the two strings, and that is the target host.

  <p>If either:

  <ul>
   <li>the target host is not a valid host name, or

   <li>the <var title="">port</var> argument is neither equal to 80, nor
    equal to 443, nor greater than or equal to 1024 and less than or equal to
    65535,
  </ul>

  <p>...then the UA must raise a <a href="#security8">security exception</a>.</p>
  <!-- XXX we should have our own port for this too, e.g. 980 -->

  <p>Otherwise, the user agent must verify that the <a href="#the-string">the
   string representing the script's domain in IDNA format</a> can be obtained
   without errors. If it cannot, then the user agent must raise a <a
   href="#security8">security exception</a>.

  <p>The user agent may also raise a <a href="#security8">security
   exception</a> at this time if, for some reason, permission to create a
   direct TCP connection to the relevant host is denied. Reasons could
   include the UA being instructed by the user to not allow direct
   connections, or the UA establishing (for instance using UPnP) that the
   network topology will cause connections on the specified port to be
   directed at the wrong host.

  <p>If no exceptions are raised by the previous steps, then a new <code><a
   href="#connection0">Connection</a></code> object must be created, its
   <code title=dom-Connection-peer><a href="#peer">peer</a></code> attribute
   must be set to a string consisting of the name of the target host, a colon
   (U+003A COLON), and the port number as decimal digits, and its <code
   title=dom-Connection-network><a href="#network1">network</a></code>
   attribute must be set to the same value as the <code
   title=dom-Connection-peer><a href="#peer">peer</a></code> attribute.

  <p>This object must then be returned.

  <p>The user agent must then begin trying to establish a connection with the
   target host and specified port. (This typically would begin in the
   backgound, while the script continues to execute.)

  <p>If the <var title="">secure</var> boolean argument is set to true, then
   the user agent must establish a secure connection with the target host and
   specified port using TLS or another protocol, negotiated with the server.
   <a href="#refsRFC2246">[RFC2246]</a> If this fails the user agent must act
   as if it had <a href="#closeConnection">closed the connection</a>.

  <p>Once a secure connection is established, or if the <var
   title="">secure</var> boolean argument is not set to true, then the user
   agent must continue to connect to the server using the protocol described
   in the section entitled <a href="#clients0">clients connecting over
   TCP</a>. All data on connections made using TLS must be sent as
   "application data".

  <p>Once the connection is established, the UA must act as described in the
   section entitled <a href="#sending0">sending and receiving data over
   TCP</a>.

  <p>User agents should allow multiple TCP connections to be established per
   host. In particular, user agents should not apply per-host HTTP connection
   limits to connections established with the <code
   title=dom-TCPConnection><a href="#tcpconnection">TCPConnection</a></code>
   constructor.

  <h4 id=broadcast><span class=secno>6.3.5. </span>Broadcast connections</h4>

  <p>The <dfn id=localbroadcastconnection
   title=dom-LocalBroadcastConnection><code>LocalBroadcastConnection()</code></dfn>
   constructor on the <code><a href="#window">Window</a></code> interface
   returns a new object implementing the <code><a
   href="#connection0">Connection</a></code> interface, set up to broadcast
   on the local network.

  <p>When this constructor is invoked, a new <code><a
   href="#connection0">Connection</a></code> object must be created.

  <p>The <code title=dom-Connection-network><a
   href="#network1">network</a></code> attribute of the object must be set to
   <a href="#the-string">the string representing the script's domain in IDNA
   format</a>. If this string cannot be obtained, then the user agent must
   raise a <a href="#security8">security exception</a> exception when the
   constructor is called.

  <p>The <code title=dom-Connection-peer><a href="#peer">peer</a></code>
   attribute must be set to the empty string.

  <p>The object must then be returned, unless, for some reason, permission to
   broadcast on the local network is to be denied. In the latter case, a <a
   href="#security8">security exception</a> must be raised instead. User
   agents may deny such permission for any reason, for example a user
   preference.

  <p>If the object is returned (i.e. if no exception is raised), the user
   agent must the begin broadcasting and listening on the local network, in
   the background, as described below. The user agent may define "the local
   network" in any way it considers appropriate and safe; for instance the
   user agent may ask the user which network (e.g. Bluetooth, IrDA, Ethernet,
   etc) the user would like to broadcast on before beginning broadcasting.

  <p>UAs may broadcast and listen on multiple networks at once. For example,
   the UA could broadcast on both Bluetooth and Wifi at the same time.</p>
  <!-- XXX bridging? how do we handle one UA not seeing
  the same hosts as another UA? -->

  <p>As soon as the object is returned, the connection <a
   href="#openConnection">has been established</a>, which implies that the
   <code title=event-connection-open><a href="#open3">open</a></code> event
   must be fired. Broadcast connections are never closed.

  <h5 id=broadcasting><span class=secno>6.3.5.1. </span>Broadcasting over
   TCP/IP</h5>

  <p class=big-issue>Should we drop this altogether? Letting people fill the
   local network with garbage seems unwise.

  <p class=big-issue>We need to register a UDP port for this. For now this
   spec refers to port 18080/udp.

  <p class=note>Since this feature requires that the user agent listen to a
   particular port, some platforms might prevent more than one user agent per
   IP address from using this feature at any one time.

  <p>On TCP/IP networks, broadcast connections transmit data using UDP over
   port 18080.

  <p>When the <code title=dom-Connection-send><a href="#send">send(<var
   title="">data</var>)</a></code> method is invoked on a <code><a
   href="#connection0">Connection</a></code> object that was created by the
   <code title=dom-LocalBroadcastConnection><a
   href="#localbroadcastconnection">LocalBroadcastConnection()</a></code>
   constructor, the user agent must follow these steps:

  <ol>
   <li>Create a string consisting of the value of the <code
    title=dom-Connection-network><a href="#network1">network</a></code>
    attribute of the <code><a href="#connection0">Connection</a></code>
    object, a U+0020 SPACE character, a U+0002 START OF TEXT character, and
    the <var title="">data</var> argument.

   <li>Encode the string as UTF-8.

   <li>If the resulting byte stream is longer than 65487 bytes, raise an
    <code>INDEX_SIZE_ERR</code> DOM exception and stop.

   <li>Create a UDP packet whose data is the byte stream, with the source and
    destination ports being 18080, and with appropriate length and checksum
    fields. Transmit this packet to IPv4 address 255.255.255.255 or IPv6
    address ff02::1, as appropriate. <span class=note>IPv6 applications will
    also have to enable reception from this address.</span>
  </ol>

  <p>When a broadcast connection is opened on a TCP/IP network, the user
   agent should listen for UDP packets on port 18080.

  <p>When the user agent receives a packet on port 18080, the user agent must
   attempt to decode that packet's data as UTF-8. If the data is not fully
   correct UTF-8 (i.e. if there are decoding errors) then the packet must be
   ignored. Otherwise, the user agent must check to see if the decoded string
   contains a U+0020 SPACE character. If it does not, then the packet must
   again be ignored (it might be a peer discovery packet from a <code
   title=dom-PeerToPeerConnection><a
   href="#peertopeerconnection">PeerToPeerConnection()</a></code>
   constructor). If it does then the user agent must split the string at the
   first space character. All the characters before the space are then known
   as <var title="">d</var>, and all the characters after the space are known
   as <var title="">s</var>. If <var title="">s</var> is not at least one
   character long, or if the first character of <var title="">s</var> is not
   a U+0002 START OF TEXT character, then the packet must be ignored. (This
   allows for future extension of this protocol.)

  <p>Otherwise, for each <code><a href="#connection0">Connection</a></code>
   object that was created by the <code title=dom-LocalBroadcastConnection><a
   href="#localbroadcastconnection">LocalBroadcastConnection()</a></code>
   constructor and whose <code title=dom-Connection-network><a
   href="#network1">network</a></code> attribute exactly matches <var
   title="">d</var>, a <code title=event-connection-read><a
   href="#read">read</a></code> event must be fired on the <code><a
   href="#connection0">Connection</a></code> object. The string <var
   title="">s</var>, with the first character removed, must be used as the
   <code title=dom-ConnectionReadEvent-data><a href="#data5">data</a></code>,
   and the source IP address of the packet as the <code
   title=dom-ConnectionReadEvent-source><a href="#source2">source</a></code>.

  <p class=big-issue>Making the source IP available means that if two or more
   machines in a private network can be made to go to a hostile page
   simultaneously, the hostile page can determine the IP addresses used
   locally (i.e. on the other side of any NAT router). Is there some way we
   can keep link-local IP addresses secret while still allowing for
   applications to distinguish between multiple participants?

  <h5 id=bluetooth-broadcast><span class=secno>6.3.5.2. </span>Broadcasting
   over Bluetooth</h5>

  <p class=big-issue>Does anyone know enough about Bluetooth to write this
   section?

  <h5 id=irda-broadcast><span class=secno>6.3.5.3. </span>Broadcasting over
   IrDA</h5>

  <p class=big-issue>Does anyone know enough about IrDA to write this
   section?

  <h4 id=peer-to-peer><span class=secno>6.3.6. </span>Peer-to-peer
   connections</h4>

  <p>The <dfn id=peertopeerconnection
   title=dom-PeerToPeerConnection><code>PeerToPeerConnection()</code></dfn>
   constructor on the <code><a href="#window">Window</a></code> interface
   returns a new object implementing the <code><a
   href="#connection0">Connection</a></code> interface, set up for a direct
   connection to a user-specified host.

  <p>When this constructor is invoked, a new <code><a
   href="#connection0">Connection</a></code> object must be created.

  <p>The <code title=dom-Connection-network><a
   href="#network1">network</a></code> attribute of the object must be set to
   <a href="#the-string">the string representing the script's domain in IDNA
   format</a>. If this string cannot be obtained, then the user agent must
   raise a <a href="#security8">security exception</a> exception when the
   constructor is called.

  <p>The <code title=dom-Connection-peer><a href="#peer">peer</a></code>
   attribute must be set to the empty string.

  <p>The object must then be returned, unless, for some reason, permission to
   establish peer-to-peer connections is generally disallowed, for example
   due to administrator settings. In the latter case, a <a
   href="#security8">security exception</a> must be raised instead.

  <p>The user agent must then, typically while the script resumes execution,
   find a remote host to establish a connection to. To do this it must start
   broadcasting and listening for peer discovery messages and listening for
   incoming connection requests on all the supported networks. How this is
   performed depends on the type of network and is described below.

  <p>The UA should inform the user of the clients that are detected, and
   allow the user to select one to connect to. UAs may also allow users to
   explicit specify hosts that were not detected, e.g. by having the user
   enter an IP address.

  <p>If an incoming connection is detected before the user specifies a target
   host, the user agent should ask the user to confirm that this is the host
   they wish to connect to. If it is, the connection should be accepted and
   the UA will act as the <em>server</em> in this connection. (Which UA acts
   as the server and which acts as the client is not discernible at the DOM
   API level.)

  <p>If no incoming connection is detected and if the user specifies a
   particular target host, a connection should be established to that host,
   with the UA acting as the <em>client</em> in the connection.

  <p>No more than one connection must be established per <code><a
   href="#connection0">Connection</a></code> object, so once a connection has
   been established, the user agent must stop listening for further
   connections (unless, or until such time as, another <code><a
   href="#connection0">Connection</a></code> object is being created).

  <p>If at any point the user cancels the connection process or the remote
   host refuses the connection, then the user agent must act as if it had <a
   href="#closeConnection">closed the connection</a>, and stop trying to
   connect.

  <h5 id=peer-to-peer0><span class=secno>6.3.6.1. </span>Peer-to-peer
   connections over TCP/IP</h5>

  <p class=big-issue>Should we replace this section with something that uses
   Rendez-vous/zeroconf or equivalent?

  <p class=big-issue>We need to register ports for this. For now this spec
   refers to port 18080/udp and 18080/tcp.

  <p class=note>Since this feature requires that the user agent listen to a
   particular port, some platforms might prevent more than one user agent per
   IP address from using this feature at any one time.

  <p>When using TCP/IP, broadcasting peer discovery messages must be done by
   creating UDP packets every few seconds containing as their data the value
   of the connection's <code title=dom-Connection-network><a
   href="#network1">network</a></code> attribute, encoded as UTF-8, with the
   source and destination ports being set to 18080 and appropriate length and
   checksum fields, and sending these packets to address (in IPv4)
   255.255.255.255 or (in IPv6) ff02::1, as appropriate.

  <p>Listening for peer discovery messages must be done by examining incoming
   UDP packets on port 18080. <span class=note>IPv6 applications will also
   have to enable reception from the ff02::1 address.</span> If their payload
   is exactly byte-for-byte equal to a UTF-8 encoded version of the value of
   the connection's <code title=dom-Connection-network><a
   href="#network1">network</a></code> attribute, then the source address of
   that packet represents the address of a host that is ready to accept a
   peer-to-peer connection, and it should therefore be offered to the user.

  <p>Incoming connection requests must be listened for on TCP port 18080. If
   an incoming connection is received, the UA must act as a <em>server</em>,
   as described in the section entitled <a href="#servers0">servers accepting
   connections over TCP</a>.

  <p>If no incoming connection requests are accepted and the user instead
   specifies a target host to connect to, the UA acts as a <em>client</em>:
   the user agent must attempt to connect to the user-specified host on port
   18080, as described in the section entitled <a href="#clients0">clients
   connecting over TCP</a>.

  <p>Once the connection is established, the UA must act as described in the
   section entitled <a href="#sending0">sending and receiving data over
   TCP</a>.

  <p class=note>This specification does not include a way to establish
   <em>secure</em> (encrypted) peer-to-peer connections at this time. <span
   class=big-issue>If you can see a good way to do this, let me know.</span>

  <h5 id=bluetooth-peer><span class=secno>6.3.6.2. </span>Peer-to-peer
   connections over Bluetooth</h5>

  <p class=big-issue>Does anyone know enough about Bluetooth to write this
   section?

  <h5 id=irda-peer><span class=secno>6.3.6.3. </span>Peer-to-peer connections
   over IrDA</h5>

  <p class=big-issue>Does anyone know enough about IrDA to write this
   section?</p>
  <!--XXX
    <p>Prompts the user to select a connection to make, which could
    look like this:</p>

<pre>|:: New Connection :::::::::::::::::::::::::::::::::::::::::|
|                                                           |
|  Select the peer to connect to:                           |
|                                                           |
|    JohnSmith_Series60   via Bluetooth      (( Connect ))  |
|    Patrick's Phone      via Bluetooth       ( Connect )   |
|    John Smith           via UDP             ( Connect )   |
|                                                           |
|                                               ( Cancel )  |
|___________________________________________________________|
</pre>

    <p>While the prompt is displayed, the UA should broadcast on all
    supported networks, as described <span title="announcing peer
    connections">below</span>.</p>

    <p>Returns null if the prompt was canceled. Otherwise, returns a
    <code>Connection</code> object with its <code>network</code>
    attribute set to <var title="">topic</var> and its <code>peer</code>
    attribute set to a string uniquely identifying the selected peer,
    and opens a connection to that peer. (See: <span>peer connection
    formats</span>.)</p>


   |:: New Connection :::::::::::::::::::::::::::::::::::::::::|
   |                                                           |
   |  Would you like to open a connection called "Chess" for   |
   |  this Web site?:                                          |
   |                                                           |
   |    example.org                                            |
   |                                                           |
   |  Select connection to use: [ Bluetooth      | v ]         |
   |                                                           |
   |                        (( Open connection ))  ( Cancel )  |
   |___________________________________________________________|

  c = new LocalBroadcastConnection("Chess");
  c.onread = function(s, f) { alert("got message " + s + " from " + f); }
  c.send("hello, anybody there?");


   |:: New Connection :::::::::::::::::::::::::::::::::::::::::|
   |                                                           |
   |  Select the peer to connect to:                           |
   |                                                           |
   |    JohnSmith_Series60   via Bluetooth      (( Connect ))  |
   |    Patrick's Phone      via Bluetooth       ( Connect )   |
   |    John Smith           via UDP             ( Connect )   |
   |                                                           |
   |                                               ( Cancel )  |
   |___________________________________________________________|

  c = new LocalPeerConnection("Chess");
  // c.peer contains peer's name
  c.onread = function(s) { alert("got message " + s); } // second argument is c.peer
  c.send("hello");

  c = new TCPConnection("chess.example.com", 8089, false);
  // c.peer contains 'chess.example.com:8089'
  c.onread = function(s) { alert("got message " + s); } // second argument is c.peer
  c.send("hello");

> > Again, what else should we support? Should this have an HTML Element
> > backing it for more declarative authoring? What error handling do we need?
> > Should it automatically use bluetooth, TCP/IP broadcast, infrared, or
> > should it be under the control of the author or user?
-->

  <h4 id=the-common><span class=secno>6.3.7. </span>The common protocol for
   TCP-based connections</h4>

  <p>The same protocol is used for <code title=dom-TCPConnection><a
   href="#tcpconnection">TCPConnection</a></code> and <code
   title=dom-PeerToPeerConnection><a
   href="#peertopeerconnection">PeerToPeerConnection</a></code> connection
   types. This section describes how such connections are established from
   the client and server sides, and then describes how data is sent and
   received over such connections (which is the same for both clients and
   servers).

  <h5 id=clients><span class=secno>6.3.7.1. </span><dfn id=clients0>Clients
   connecting over TCP</dfn></h5>

  <p>This section defines the client-side requirements of the protocol used
   by the <code title=dom-TCPConnection><a
   href="#tcpconnection">TCPConnection</a></code> and <code
   title=dom-PeerToPeerConnection><a
   href="#peertopeerconnection">PeerToPeerConnection</a></code> connection
   types.

  <p>If a TCP connection to the specified target host and port cannot be
   established, for example because the target host is a domain name that
   cannot be resolved to an IP address, or because packets cannot be routed
   to the host, the user agent should retry creating the connection. If the
   user agent gives up trying to connect, the user agent must act as if it
   had <a href="#closeConnection">closed the connection</a>.

  <p class=note>No information regarding the state of the connection is
   passed to the application while the connection is being established in
   this version of this specification.

  <p>Once a TCP/IP connection to the remote host is established, the user
   agent must transmit the following sequence of bytes, represented here in
   hexadecimal form:

  <pre>0x48 0x65 0x6C 0x6C 0x6F 0x0A</pre>

  <p class=note>This represents the string "Hello" followed by a newline,
   encoded in UTF-8.

  <p>The user agent must then read all the bytes sent from the remote host,
   up to the first 0x0A byte (inclusive). That string of bytes is then
   compared byte-for-byte to the following string of bytes:

  <pre>0x57 0x65 0x6C 0x63 0x6F 0x6E 0x65 0x0A</pre>

  <p class=note>This says "Welcome".

  <p>If the server sent back a string in any way different to this, then the
   user agent must <a href="#closeConnection">close the connection</a> and
   give up trying to connect.

  <p>Otherwise, the user agent must then take <a href="#the-string">the
   string representing the script's domain in IDNA format</a>, encode it as
   UTF-8, and send that to the remote host, followed by a 0x0A byte (a U+000A
   LINE FEED in UTF-8).

  <p>The user agent must then read all the bytes sent from the remote host,
   up to the first 0x0A byte (inclusive). That string of bytes must then be
   compared byte-for-byte to the string that was just sent to the server (the
   one with the IDNA domain name and ending with a newline character). If the
   server sent back a string in any way different to this, then the user
   agent must <a href="#closeConnection">close the connection</a> and give up
   trying to connect.

  <p>Otherwise, the connection <a href="#openConnection">has been
   established</a> (and events and so forth get fired, as described above).

  <p>If at any point during this process the connection is closed
   prematurely, then the user agent must <a href="#closeConnection">close the
   connection</a> and give up trying to connect.</p>
  <!-- XXX we should support automatic reconnect -->

  <h5 id=servers><span class=secno>6.3.7.2. </span><dfn id=servers0>Servers
   accepting connections over TCP</dfn></h5>

  <p>This section defines the server side of the protocol described in the
   previous section. For authors, it should be used as a guide for how to
   implement servers that can communicate with Web pages over TCP. For UAs
   these are the requirements for the server part of <code
   title=dom-PeerToPeerConnection><a
   href="#peertopeerconnection">PeerToPeerConnection</a></code>s.

  <p>Once a TCP/IP connection from a remote host is established, the user
   agent must transmit the following sequence of bytes, represented here in
   hexadecimal form:

  <pre>0x57 0x65 0x6C 0x63 0x6F 0x6E 0x65 0x0A</pre>

  <p class=note>This says "Welcome" and a newline in UTF-8.

  <p>The user agent must then read all the bytes sent from the remote host,
   up to the first 0x0A byte (inclusive). That string of bytes is then
   compared byte-for-byte to the following string of bytes:

  <pre>0x48 0x65 0x6C 0x6C 0x6F 0x0A</pre>

  <p class=note>"Hello" and a newline.

  <p>If the remote host sent back a string in any way different to this, then
   the user agent must <a href="#closeConnection">close the connection</a>
   and give up trying to connect.

  <p>Otherwise, the user agent must then take <a href="#the-string">the
   string representing the script's domain in IDNA format</a>, encode it as
   UTF-8, and send that to the remote host, followed by a 0x0A byte (a U+000A
   LINE FEED in UTF-8).

  <p>The user agent must then read all the bytes sent from the remote host,
   up to the first 0x0A byte (inclusive). That string of bytes must then be
   compared byte-for-byte to the string that was just sent to that host (the
   one with the IDNA domain name and ending with a newline character). If the
   remote host sent back a string in any way different to this, then the user
   agent must <a href="#closeConnection">close the connection</a> and give up
   trying to connect.

  <p>Otherwise, the connection <a href="#openConnection">has been
   established</a> (and events and so forth get fired, as described above).

  <p class=note>For author-written servers (as opposed to the server side of
   a peer-to-peer connection), the script's domain would be replaced by the
   hostname of the server. Alternatively, such servers might instead wait for
   the client to send its domain string, and then simply echo it back. This
   would allow connections from pages on any domain, instead of just pages
   originating from the same host. The client compares the two strings to
   ensure they are the same before allowing the connection to be used by
   author script.

  <p>If at any point during this process the connection is closed
   prematurely, then the user agent must <a href="#closeConnection">close the
   connection</a> and give up trying to connect.</p>
  <!-- XXX we should support automatic reconnect -->

  <h5 id=sending><span class=secno>6.3.7.3. </span><dfn id=sending0>Sending
   and receiving data over TCP</dfn></h5>

  <p>When the <code title=dom-Connection-send><a href="#send">send(<var
   title="">data</var>)</a></code> method is invoked on the connection's
   corresponding <code><a href="#connection0">Connection</a></code> object,
   the user agent must take the <var title="">data</var> argument, replace
   any U+0000 NULL and U+0017 END OF TRANSMISSION BLOCK characters in it with
   U+FFFD REPLACEMENT CHARACTER characters, then transmit a U+0002 START OF
   TEXT character, this new <var title="">data</var> string and a single
   U+0017 END OF TRANSMISSION BLOCK character (in that order) to the remote
   host, all encoded as UTF-8.

  <p>When the user agent receives bytes on the connection, the user agent
   must buffer received bytes until it receives a 0x17 byte (a U+0017 END OF
   TRANSMISSION BLOCK character). If the first buffered byte is not a 0x02
   byte (a U+0002 START OF TEXT character encoded as UTF-8) then all the data
   up to the 0x17 byte, inclusive, must be dropped. (This allows for future
   extension of this protocol.) Otherwise, all the data from (but not
   including) the 0x02 byte and up to (but not including) the 0x17 byte must
   be taken, interpreted as a UTF-8 string, and a <code
   title=event-connection-read><a href="#read">read</a></code> event must be
   fired on the <code><a href="#connection0">Connection</a></code> object
   with that string as the <code title=dom-ConnectionReadEvent-data><a
   href="#data5">data</a></code>. If that string cannot be decoded as UTF-8
   without errors, the packet should be ignored.

  <p class=note>This protocol does not yet allow binary data (e.g. an image
   or <a href="#media7">media data</a>) to be efficiently transmitted. A
   future version of this protocol might allow this by using the prefix
   character U+001F INFORMATION SEPARATOR ONE, followed by binary data which
   uses a particular byte (e.g. 0xFF) to encode byte 0x17 somehow (since
   otherwise 0x17 would be treated as transmission end by down-level UAs).</p>
  <!--
    Specifically, replace all occurrences of 0xFF with 0xFF 0xFF and
    all occurrences of 0x17 with 0xFF 0x00, or similar.
   -->

  <h4 id=network-security><span class=secno>6.3.8. </span>Security</h4>

  <p class=big-issue>Need to write this section.

  <p class=big-issue>If you have an unencrypted page that is (through a
   man-in-the-middle attack) changed, it can access a secure service that is
   using IP authentication and then send that data back to the attacker. Ergo
   we should probably stop unencrypted pages from accessing encrypted
   services, on the principle that the actual level of security is zero. Then
   again, if we do that, we prevent insecure sites from using SSL as a
   tunneling mechanism.

  <p class=big-issue>Should consider dropping the subdomain-only restriction.
   It doesn't seem to add anything, and prevents cross-domain chatter.

  <h4 id=network-other-specs><span class=secno>6.3.9. </span>Relationship to
   other standards</h4>

  <p class=big-issue>Should have a section talking about the fact that we
   blithely ignoring IANA's port assignments here.

  <p class=big-issue>Should explain why we are not reusing HTTP for this.
   (HTTP is too heavy-weight for such a simple need; requiring authors to
   implement an HTTP server just to have a party line is too much of a
   barrier to entry; cannot rely on prebuilt components; having a simple
   protocol makes it much easier to do RAD; HTTP doesn't fit the needs and
   doesn't have the security model needed; etc)

  <h3 id=crossDocumentMessages><span class=secno>6.4. </span><dfn
   id=cross-document>Cross-document messaging</dfn></h3>

  <p>Web browsers, for security and privacy reasons, prevent documents in
   different domains from affecting each other; that is, cross-site scripting
   is disallowed.

  <p>While this is an important security feature, it prevents pages from
   different domains from communicating even when those pages are not
   hostile. This section introduces a messaging system that allows documents
   to communicate with each other regardless of their source domain, in a way
   designed to not enable cross-site scripting attacks.

  <p class=big-issue>We may want to just put postMessage on Window instead of
   Document, as that reduces the XSS risk.

  <h4 id=processing1><span class=secno>6.4.1. </span>Processing model</h4>

  <p>When a script invokes the <dfn id=postmessage
   title=dom-document-postMessage><code>postMessage(<var
   title="">message</var>)</code></dfn> method on a <code>Document</code>
   object, the user agent must create an event that uses the <code><a
   href="#messageevent">MessageEvent</a></code> interface, with the event
   name <code title=event-message><a href="#message">message</a></code>,
   which bubbles, is cancelable, and has no default action. The <code
   title=dom-MessageEvent-data><a href="#data4">data</a></code> attribute
   must be set to the value passed as the <var title="">message</var>
   argument to the <code title=dom-document-postMessage><a
   href="#postmessage">postMessage()</a></code> method, the <code
   title=dom-MessageEvent-domain><a href="#domain2">domain</a></code>
   attribute must be set to the domain of the document that the script that
   invoked the methods is associated with, the <code
   title=dom-MessageEvent-uri><a href="#uri">uri</a></code> attribute must be
   set to the URI of that document, and the <code
   title=dom-MessageEvent-source><a href="#source1">source</a></code>
   attribute must be set to the <code>Document</code> object representing
   that document.

  <p>The event must then be dispatched at the <code>Document</code> object
   itself.</p>
  <!-- XXX must ensure that postMessage() is accessible on
  cross-domain Document objects but that the dispatchEvent() method is
  not. -->

  <p class=warning>Authors should check the <code
   title=dom-MessageEvent-domain><a href="#domain2">domain</a></code>
   attribute to ensure that messages are only accepted from domains that they
   expect to receive messages from. Otherwise, bugs in the author's message
   handling code could be exploited by hostile sites.

  <div class=example>
   <p>For example, if document A contains an <code><a
    href="#object">object</a></code> element that contains document B, and
    script in document A calls <code title=dom-document-postMessage><a
    href="#postmessage">postMessage()</a></code> on document B, then a
    message event will be fired on that element, marked as originating from
    document A. The script in document A might look like:</p>

   <pre>var o = document.getElementsByTagName('object')[0];
o.<span title="">contentDocument</span>.<a href="#postmessage" title=dom-document-postMessage>postMessage</a>('Hello world');
</pre>

   <p>To register an event handler for incoming events, the script would use
    <code title="">addEventListener()</code> (or similar mechanisms). For
    example, the script in document B might look like:</p>

   <pre>document.addEventListener('message', receiver, false);
function receiver(e) {
  if (e.domain == 'example.com') {
    if (e.data == 'Hello world') {
      e.source.postMessage('Hello');
    } else {
      alert(e.data);
    }
  }
}</pre>

   <p>This script first checks the domain is the expected domain, and then
    looks at the message, which it either displays to the user, or responds
    to by sending a message back to the document which sent the message in
    the first place.</p>
  </div>

  <p class=note>Implementors are urged to take extra care in the
   implementation of this feature. It allows authors to transmit information
   from one domain to another domain, which is normally disallowed for
   security reasons. It also requires that UAs be careful to allow access to
   certain properties but not others.

  <h2 id=repetition><span class=secno>7. </span>Repetition templates</h2>

  <p class=big-issue>See <a
   href="http://www.whatwg.org/specs/web-forms/current-work/#repeatingFormControls">WF2</a>
   for now

  <h2 id=syntax><span class=secno>8. </span>The HTML syntax</h2>

  <h3 id=writing><span class=secno>8.1. </span>Writing HTML documents</h3>

  <p><em>This section only applies to documents, authoring tools, and markup
   generators. In particular, it does not apply to conformance checkers;
   conformance checkers must use the requirements given in the next section
   ("parsing HTML documents").</em>

  <p>Documents must consist of the following parts, in the given order:

  <ol>
   <li>Optionally, a single U+FEFF BYTE ORDER MARK (BOM) character.

   <li>Any number of <a href="#comments0" title=syntax-comments>comments</a>
    and <a href="#space" title="space character">space characters</a>.

   <li>A <a href="#doctype" title=syntax-doctype>DOCTYPE</a>.

   <li>Any number of <a href="#comments0" title=syntax-comments>comments</a>
    and <a href="#space" title="space character">space characters</a>.

   <li>The root element, in the form of an <code><a
    href="#html">html</a></code> <a href="#elements2"
    title=syntax-elements>element</a>.

   <li>Any number of <a href="#comments0" title=syntax-comments>comments</a>
    and <a href="#space" title="space character">space characters</a>.
  </ol>

  <p>The various types of content mentioned above are described in the next
   few sections.

  <p>In addition, there are some restrictions on how <a href="#charset0"
   title=attr-meta-charset>character encoding declarations</a> are to be
   serialised, as discussed in the section on that topic.

  <h4 id=the-doctype><span class=secno>8.1.1. </span>The DOCTYPE</h4>

  <p>A <dfn id=doctype title=syntax-doctype>DOCTYPE</dfn> is a mostly
   useless, but required, header.

  <p class=note>DOCTYPEs are required for legacy reasons. When omitted,
   browsers tend to use a different rendering mode that is incompatible with
   some specifications. Including the DOCTYPE in a document ensures that the
   browser makes a best-effort attempt at following the relevant
   specifications.

  <p>A DOCTYPE must consist of the following characters, in this order:

  <ol class=brief>
   <li>A U+003C LESS-THAN SIGN (<code>&lt;</code>) character.

   <li>A U+0021 EXCLAMATION MARK (<code>!</code>) character.

   <li>A U+0044 LATIN CAPITAL LETTER D or U+0064 LATIN SMALL LETTER D
    character.

   <li>A U+004F LATIN CAPITAL LETTER O or U+006F LATIN SMALL LETTER O
    character.

   <li>A U+0043 LATIN CAPITAL LETTER C or U+0063 LATIN SMALL LETTER C
    character.

   <li>A U+0054 LATIN CAPITAL LETTER T or U+0074 LATIN SMALL LETTER T
    character.

   <li>A U+0059 LATIN CAPITAL LETTER Y or U+0079 LATIN SMALL LETTER Y
    character.

   <li>A U+0050 LATIN CAPITAL LETTER P or U+0070 LATIN SMALL LETTER P
    character.

   <li>A U+0045 LATIN CAPITAL LETTER E or U+0065 LATIN SMALL LETTER E
    character.

   <li>One or more <a href="#space" title="space character">space
    characters</a>.

   <li>A U+0048 LATIN CAPITAL LETTER H or U+0068 LATIN SMALL LETTER H
    character.

   <li>A U+0054 LATIN CAPITAL LETTER T or U+0074 LATIN SMALL LETTER T
    character.

   <li>A U+004D LATIN CAPITAL LETTER M or U+006D LATIN SMALL LETTER M
    character.

   <li>A U+004C LATIN CAPITAL LETTER L or U+006C LATIN SMALL LETTER L
    character.

   <li>Zero or more <a href="#space" title="space character">space
    characters</a>.

   <li>A U+003E GREATER-THAN SIGN (<code>&gt;</code>) character.
  </ol>

  <p class=note>In other words, <code>&lt;!DOCTYPE HTML></code>,
   case-insensitively.

  <h4 id=elements0><span class=secno>8.1.2. </span>Elements</h4>

  <p>There are four different kinds of <dfn id=elements2
   title=syntax-elements>elements</dfn>: void elements, CDATA elements,
   RCDATA elements, and normal elements.

  <dl>
   <dt>Void elements

   <dd><code><a href="#base">base</a></code>, <code><a
    href="#link">link</a></code>, <code><a href="#meta0">meta</a></code>,
    <code><a href="#hr">hr</a></code>, <code><a href="#br">br</a></code>,
    <code><a href="#img">img</a></code>, <code><a
    href="#embed">embed</a></code>, <code><a href="#param">param</a></code>,
    <code><a href="#area">area</a></code>, <code><a
    href="#col">col</a></code>, <code>input</code><!-- XXX add: ,
   <code>command</code>, <code>event-source</code> --></dd>
   <!-- XXX
   keep this synchronised with the list of "permitted slash" elements
   -->

   <dt>CDATA elements

   <dd><code><a href="#style">style</a></code>, <code><a
    href="#script0">script</a></code></dd>
   <!-- iframe and
   noscript don't count as CDATA for syntax purposes -->

   <dt>RCDATA elements

   <dd><code><a href="#title1">title</a></code>, <code>textarea</code>

   <dt>Normal elements

   <dd>All other allowed HTML elements are normal elements.
  </dl>

  <p><dfn id=tags title=syntax-tags>Tags</dfn> are used to delimit the start
   and end of elements in the markup. CDATA, RCDATA, and normal elements have
   a <a href="#start5" title=syntax-start-tags>start tag</a> to indicate
   where they begin, and an <a href="#end-tags0" title=syntax-end-tags>end
   tag</a> to indicate where they end. The start and end tags of certain
   normal elements can be <a href="#omitted"
   title=syntax-tag-omission>omitted</a>, as described later. Those that
   cannot be omitted must not be omitted. Void elements only have a start
   tag; end tags must not be specified for void elements.

  <p>The contents of the element must be placed between just after the start
   tag (which <a href="#omitted" title=syntax-tag-omission>might be implied,
   in certain cases</a>) and just before the end tag (which again, <a
   href="#omitted" title=syntax-tag-omission>might be implied in certain
   cases</a>). The exact allowed contents of each individual element depends
   on the content model of that element, as described earlier in this
   specification. Elements must not contain content that their content model
   disallows. In addition to the restrictions placed on the contents by those
   content models, however, the four types of elements have additional
   <em>syntactic</em> requirements.

  <p>Void elements can't have any contents (since there's no end tag, no
   content can be put between the start tag and the end tag.)

  <p>CDATA elements can have <a href="#text1" title=syntax-text>text</a>,
   but:

  <ul>
   <li>The text must not contain the two character sequence "<code
    title="">&lt;/</code>" (U+003C LESS-THAN SIGN, U+002F SOLIDUS).

   <li>For every occurrence of the four character sequence "<code
    title="">&lt;!--</code>" (U+003C LESS-THAN SIGN, U+0021 EXCLAMATION MARK,
    U+002D HYPHEN-MINUS, U+002D HYPHEN-MINUS), there must be a corresponding
    three-character sequence "<code title="">--&gt;</code>" (U+002D
    HYPHEN-MINUS, U+002D HYPHEN-MINUS, U+003E GREATER-THAN SIGN) whose U+003E
    GREATER-THAN SIGN (&gt;) character occurs later in the text than the
    U+003C LESS-THAN SIGN (&lt;) character of the first sequence. (This means
    the hyphens from the "<code title="">&lt;!--</code>" part can overlap
    those in the "<code title="">--&gt;</code>" part, as in "<code
    title="">&lt!--&gt;</code>".)
  </ul>

  <p>RCDATA elements can have <a href="#text1" title=syntax-text>text</a> and
   <a href="#character0" title=syntax-entities>character entity
   references</a>, but the text must not contain the character U+003C
   LESS-THAN SIGN (<code>&lt;</code>) or the character U+0026 AMPERSAND
   (<code>&amp;</code>).

  <p>Normal elements can have <a href="#text1" title=syntax-text>text</a>, <a
   href="#character0" title=syntax-entities>character entity references</a>,
   other <a href="#elements2" title=syntax-elements>elements</a>, and <a
   href="#comments0" title=syntax-comments>comments</a>, but the text must
   not contain the character U+003C LESS-THAN SIGN (<code>&lt;</code>) or the
   character U+0026 AMPERSAND (<code>&amp;</code>). Some normal elements also
   have <a href="#have-extra" title=syntax-element-restrictions>yet more
   restrictions</a> on what content they are allowed to hold, beyond the
   restrictions imposed by the content model and those described in this
   paragraph. Those restrictions are described below.

  <p>Tags contain a <dfn id=tag-name title=syntax-tag-name>tag name</dfn>,
   giving the element's name. HTML elements all have names that only use
   characters in the range U+0061 LATIN SMALL LETTER A .. U+007A LATIN SMALL
   LETTER Z, or, in uppercase, U+0041 LATIN CAPITAL LETTER A .. U+005A LATIN
   CAPITAL LETTER Z, and U+002D HYPHEN-MINUS (<code>-</code>). In the HTML
   syntax, tag names may be written with any mix of lower- and uppercase
   letters that, when converted to all-lowercase, matches the element's tag
   name; tag names are case-insensitive.

  <h5 id=start><span class=secno>8.1.2.1. </span>Start tags</h5>

  <p><dfn id=start5 title=syntax-start-tags>Start tags</dfn> must have the
   following format:

  <ol>
   <li>The first character of a start tag must be a U+003C LESS-THAN SIGN
    (<code>&lt;</code>).

   <li>The next few characters of a start tag must be the element's <a
    href="#tag-name" title=syntax-tag-name>tag name</a>.

   <li>If there are to be any attributes in the next step, there must first
    be one or more <a href="#space" title="space character">space
    characters</a>.

   <li>Then, the start tag may have a number of attributes, the <a
    href="#attributes1" title=syntax-attributes>syntax for which</a> is
    described below. Attributes may be separated from each other by one or
    more <a href="#space" title="space character">space characters</a>.

   <li>After the attributes, there may be one or more <a href="#space"
    title="space character">space characters</a>. (Some attributes are
    required to be followed by a space. See the <a href="#attributes1"
    title=syntax-attributes>attributes section</a> below.)

   <li>Then, if the element is one of the void elements, then there may be a
    single U+002F SOLIDUS (<code>/</code>) character. This character has no
    effect except to appease the markup gods. As this character is therefore
    just a symbol of faith, atheists should omit it.

   <li>Finally, start tags must be closed by a U+003E GREATER-THAN SIGN
    (<code>&gt;</code>) character.
  </ol>

  <h5 id=end-tags><span class=secno>8.1.2.2. </span>End tags</h5>

  <p><dfn id=end-tags0 title=syntax-end-tags>End tags</dfn> must have the
   following format:

  <ol>
   <li>The first character of an end tag must be a U+003C LESS-THAN SIGN
    (<code>&lt;</code>).

   <li>The second character of an end tag must be a U+002F SOLIDUS
    (<code>/</code>).

   <li>The next few characters of an end tag must be the element's <a
    href="#tag-name" title=syntax-tag-name>tag name</a>.

   <li>After the tag name, there may be one or more <a href="#space"
    title="space character">space characters</a>.

   <li>Finally, end tags must be closed by a U+003E GREATER-THAN SIGN
    (<code>&gt;</code>) character.
  </ol>

  <h5 id=attributes0><span class=secno>8.1.2.3. </span>Attributes</h5>

  <p><dfn id=attributes1 title=syntax-attributes>Attributes</dfn> for an
   element are expressed inside the element's start tag.

  <p>Attributes have a name and a value. <dfn id=attribute
   title=syntax-attribute-name>Attribute names</dfn> use characters in the
   range U+0061 LATIN SMALL LETTER A .. U+007A LATIN SMALL LETTER Z, or, in
   uppercase, U+0041 LATIN CAPITAL LETTER A .. U+005A LATIN CAPITAL LETTER Z,
   and U+002D HYPHEN-MINUS (<code>-</code>). In the HTML syntax, attribute
   names may be written with any mix of lower- and uppercase letters that,
   when converted to all-lowercase, matches the attribute's name; attribute
   names are case-insensitive.

  <p><dfn id=attribute0 title=syntax-attribute-value>Attribute values</dfn>
   are a mixture of <a href="#text1" title=syntax-text>text</a> and <a
   href="#character0" title=syntax-entities>character entity references</a>,
   except with the additional restriction that the text cannot contain a
   U+0026 AMPERSAND (<code>&amp;</code>) character.

  <p>Attributes can be specified in four different ways:

  <dl>
   <dt>Empty attribute syntax

   <dd>
    <p>Just the <a href="#attribute" title=syntax-attribute-name>attribute
     name</a>.</p>

    <div class=example>
     <p>In the following example, the <code
      title=attr-input-disabled>disabled</code> attribute is given with the
      empty attribute syntax:</p>

     <pre>&lt;input <em>disabled</em>&gt;</pre>
    </div>

    <p>If an attribute using the empty attribute syntax is to be followed by
     another attribute, then there must be a <a href="#space">space
     character</a> separating the two.</p>

   <dt>Unquoted attribute value syntax

   <dd>
    <p>The <a href="#attribute" title=syntax-attribute-name>attribute
     name</a>, followed by zero or more <a href="#space" title="space
     character">space characters</a>, followed by a single U+003D EQUALS SIGN
     character, followed by zero or more <a href="#space" title="space
     character">space characters</a>, followed by the <a href="#attribute0"
     title=syntax-attribute-value>attribute value</a>, which, in addition to
     the requirements given above for attribute values, must not contain any
     literal <a href="#space" title="space character">space characters</a>,
     U+003E GREATER-THAN SIGN (<code>&gt;</code>) characters, or U+003C
     LESS-THAN SIGN (<code>&lt;</code>) characters, and must not,
     furthermore, start with either a literal U+0022 QUOTATION MARK
     (<code>&#x22;</code>) character or a literal U+0027 APOSTROPHE
     (<code>&#x27;</code>) character.</p>

    <div class=example>
     <p>In the following example, the <code
      title=attr-input-value>value</code> attribute is given with the
      unquoted attribute value syntax:</p>

     <pre>&lt;input <em>value=yes</em>&gt;</pre>
    </div>

    <p>If an attribute using the unquoted attribute syntax is to be followed
     by another attribute or by one of the optional U+002F SOLIDUS
     (<code>/</code>) characters allowed in step 6 of the <span
     title=syntax-start-tag>start tag</span> syntax above, then there must be
     a <a href="#space">space character</a> separating the two.</p>

   <dt>Single-quoted attribute value syntax

   <dd>
    <p>The <a href="#attribute" title=syntax-attribute-name>attribute
     name</a>, followed by zero or more <a href="#space" title="space
     character">space characters</a>, followed by a single U+003D EQUALS SIGN
     character, followed by zero or more <a href="#space" title="space
     character">space characters</a>, followed by a single U+0027 APOSTROPHE
     (<code>'</code>) character, followed by the <a href="#attribute0"
     title=syntax-attribute-value>attribute value</a>, which, in addition to
     the requirements given above for attribute values, must not contain any
     literal U+0027 APOSTROPHE (<code>'</code>) characters, and finally
     followed by a second single U+0027 APOSTROPHE (<code>'</code>)
     character.</p>

    <div class=example>
     <p>In the following example, the <code title=attr-input-type>type</code>
      attribute is given with the single-quoted attribute value syntax:</p>

     <pre>&lt;input <em>type='checkbox'</em>&gt;</pre>
    </div>

   <dt>Double-quoted attribute value syntax

   <dd>
    <p>The <a href="#attribute" title=syntax-attribute-name>attribute
     name</a>, followed by zero or more <a href="#space" title="space
     character">space characters</a>, followed by a single U+003D EQUALS SIGN
     character, followed by zero or more <a href="#space" title="space
     character">space characters</a>, followed by a single U+0022 QUOTATION
     MARK (<code>"</code>) character, followed by the <a href="#attribute0"
     title=syntax-attribute-value>attribute value</a>, which, in addition to
     the requirements given above for attribute values, must not contain any
     literal U+0022 QUOTATION MARK (<code>"</code>) characters, and finally
     followed by a second single U+0022 QUOTATION MARK (<code>"</code>)
     character.</p>

    <div class=example>
     <p>In the following example, the <code title=attr-input-name>name</code>
      attribute is given with the double-quoted attribute value syntax:</p>

     <pre>&lt;input <em>name="be evil"</em>&gt;</pre>
    </div>
  </dl>

  <h5 id=optional><span class=secno>8.1.2.4. </span>Optional tags</h5>

  <p>Certain tags can be <dfn id=omitted
   title=syntax-tag-omission>omitted</dfn>.</p>
  <!-- <html> -->

  <p>An <code><a href="#html">html</a></code> element's <span
   title=syntax-start-tag>start tag</span> may be omitted if the first thing
   inside the <code><a href="#html">html</a></code> element is not a <a
   href="#space">space character</a> or a <a href="#comments0"
   title=syntax-comments>comment</a>.</p>
  <!-- </html> -->

  <p>An <code><a href="#html">html</a></code> element's <span
   title=syntax-end-tag>end tag</span> may be omitted if the <code><a
   href="#html">html</a></code> element is not immediately followed by a <a
   href="#space">space character</a> or a <a href="#comments0"
   title=syntax-comments>comment</a>.</p>
  <!-- <head> -->

  <p>A <code><a href="#head">head</a></code> element's <span
   title=syntax-start-tag>start tag</span> may be omitted if the first thing
   inside the <code><a href="#head">head</a></code> element is an element.</p>
  <!-- </head> -->

  <p>A <code><a href="#head">head</a></code> element's <span
   title=syntax-end-tag>end tag</span> may be omitted if the <code><a
   href="#head">head</a></code> element is not immediately followed by a <a
   href="#space">space character</a> or a <a href="#comments0"
   title=syntax-comments>comment</a>.</p>
  <!-- <body> -->

  <p>A <code><a href="#body0">body</a></code> element's <span
   title=syntax-start-tag>start tag</span> may be omitted if the first thing
   inside the <code><a href="#body0">body</a></code> element is not a <a
   href="#space">space character</a> or a <a href="#comments0"
   title=syntax-comments>comment</a>, except if the first thing inside the
   <code><a href="#body0">body</a></code> element is a <code><a
   href="#script0">script</a></code> or <code><a
   href="#style">style</a></code> element and the node immediately preceding
   the <code><a href="#body0">body</a></code> element is a <code><a
   href="#head">head</a></code> element whose end tag has been omitted.</p>
  <!-- </body> -->

  <p>A <code><a href="#body0">body</a></code> element's <span
   title=syntax-end-tag>end tag</span> may be omitted if the <code><a
   href="#body0">body</a></code> element is not immediately followed by a <a
   href="#space">space character</a> or a <a href="#comments0"
   title=syntax-comments>comment</a>. <!-- </li> -->

  <p>A <code><a href="#li">li</a></code> element's <span
   title=syntax-end-tag>end tag</span> may be omitted if the <code><a
   href="#li">li</a></code> element is immediately followed by another
   <code><a href="#li">li</a></code> element or if there is no more content
   in the parent element.</p>
  <!-- </dt> -->

  <p>A <code><a href="#dt">dt</a></code> element's <span
   title=syntax-end-tag>end tag</span> may be omitted if the <code><a
   href="#dt">dt</a></code> element is immediately followed by another
   <code><a href="#dt">dt</a></code> element or a <code><a
   href="#dd">dd</a></code> element.</p>
  <!-- </dd> -->

  <p>A <code><a href="#dd">dd</a></code> element's <span
   title=syntax-end-tag>end tag</span> may be omitted if the <code><a
   href="#dd">dd</a></code> element is immediately followed by another
   <code><a href="#dd">dd</a></code> element or a <code><a
   href="#dt">dt</a></code> element, or if there is no more content in the
   parent element.</p>
  <!-- </p> -->

  <p>A <code><a href="#p">p</a></code> element's <span
   title=syntax-end-tag>end tag</span> may be omitted if the <code><a
   href="#p">p</a></code> element is immediately followed by an <code><a
   href="#address">address</a></code>, <code><a
   href="#blockquote">blockquote</a></code>, <code><a
   href="#dl">dl</a></code>, <code>fieldset</code>, <code>form</code>,
   <code><a href="#h1">h1</a></code>, <code><a href="#h2">h2</a></code>,
   <code><a href="#h3">h3</a></code>, <code><a href="#h4">h4</a></code>,
   <code><a href="#h5">h5</a></code>, <code><a href="#h6">h6</a></code>,
   <code><a href="#hr">hr</a></code>, <code><a href="#menu">menu</a></code>,
   <code><a href="#ol">ol</a></code>, <code><a href="#p">p</a></code>,
   <code><a href="#pre">pre</a></code>, <code><a
   href="#table">table</a></code>, or <code><a href="#ul">ul</a></code>
   element, or if there is no more content in the parent element.</p>
  <!-- </optgroup> -->

  <p>An <code>optgroup</code> element's <span title=syntax-end-tag>end
   tag</span> may be omitted if the <code>optgroup</code> element is
   immediately followed by another <code>optgroup</code> element, or if there
   is no more content in the parent element.</p>
  <!-- </option> -->

  <p>An <code>option</code> element's <span title=syntax-end-tag>end
   tag</span> may be omitted if the <code>option</code> element is
   immediately followed by another <code>option</code> element, or if there
   is no more content in the parent element.</p>
  <!-- <colgroup> -->

  <p>A <code><a href="#colgroup">colgroup</a></code> element's <span
   title=syntax-start-tag>start tag</span> may be omitted if the first thing
   inside the <code><a href="#colgroup">colgroup</a></code> element is a
   <code><a href="#col">col</a></code> element, and if the element is not
   immediately preceeded by another <code><a
   href="#colgroup">colgroup</a></code> element whose <span
   title=syntax-end-tag>end tag</span> has been omitted.</p>
  <!-- </colgroup> -->

  <p>A <code><a href="#colgroup">colgroup</a></code> element's <span
   title=syntax-end-tag>end tag</span> may be omitted if the <code><a
   href="#colgroup">colgroup</a></code> element is not immediately followed
   by a <a href="#space">space character</a> or a <a href="#comments0"
   title=syntax-comments>comment</a>.</p>
  <!-- </thead> -->

  <p>A <code><a href="#thead0">thead</a></code> element's <span
   title=syntax-end-tag>end tag</span> may be omitted if the <code><a
   href="#thead0">thead</a></code> element is immediately followed by a
   <code><a href="#tbody">tbody</a></code> or <code><a
   href="#tfoot0">tfoot</a></code> element.</p>
  <!-- <tbody> -->

  <p>A <code><a href="#tbody">tbody</a></code> element's <span
   title=syntax-start-tag>start tag</span> may be omitted if the first thing
   inside the <code><a href="#tbody">tbody</a></code> element is a <code><a
   href="#tr">tr</a></code> element, and if the element is not immediately
   preceeded by a <code><a href="#tbody">tbody</a></code>, <code><a
   href="#thead0">thead</a></code>, or <code><a
   href="#tfoot0">tfoot</a></code> element whose <span
   title=syntax-end-tag>end tag</span> has been omitted.</p>
  <!-- </tbody> -->

  <p>A <code><a href="#tbody">tbody</a></code> element's <span
   title=syntax-end-tag>end tag</span> may be omitted if the <code><a
   href="#tbody">tbody</a></code> element is immediately followed by a
   <code><a href="#tbody">tbody</a></code> or <code><a
   href="#tfoot0">tfoot</a></code> element, or if there is no more content in
   the parent element.</p>
  <!-- </tfoot> -->

  <p>A <code><a href="#tfoot0">tfoot</a></code> element's <span
   title=syntax-end-tag>end tag</span> may be omitted if the <code><a
   href="#tfoot0">tfoot</a></code> element is immediately followed by a
   <code><a href="#tbody">tbody</a></code> element, or if there is no more
   content in the parent element.</p>
  <!-- </tr> -->

  <p>A <code><a href="#tr">tr</a></code> element's <span
   title=syntax-end-tag>end tag</span> may be omitted if the <code><a
   href="#tr">tr</a></code> element is immediately followed by another
   <code><a href="#tr">tr</a></code> element, or if there is no more content
   in the parent element.</p>
  <!-- </td> -->

  <p>A <code><a href="#td">td</a></code> element's <span
   title=syntax-end-tag>end tag</span> may be omitted if the <code><a
   href="#td">td</a></code> element is immediately followed by a <code><a
   href="#td">td</a></code> or <code><a href="#th">th</a></code> element, or
   if there is no more content in the parent element.</p>
  <!-- </th> -->

  <p>A <code><a href="#th">th</a></code> element's <span
   title=syntax-end-tag>end tag</span> may be omitted if the <code><a
   href="#th">th</a></code> element is immediately followed by a <code><a
   href="#td">td</a></code> or <code><a href="#th">th</a></code> element, or
   if there is no more content in the parent element.

  <p><strong>However</strong>, a <span title=syntax-start-tag>start
   tag</span> must never be omitted if it has any attributes.

  <h5 id=restrictions><span class=secno>8.1.2.5. </span>Restrictions on
   content models</h5>

  <p>For historical reasons, certain elements <dfn id=have-extra
   title=syntax-element-restrictions>have extra restrictions</dfn> beyond
   even the restrictions given by their content model.

  <p>A <code><a href="#p">p</a></code> element must not contain <code><a
   href="#blockquote">blockquote</a></code>, <code><a
   href="#dl">dl</a></code>, <code><a href="#menu">menu</a></code>, <code><a
   href="#ol">ol</a></code>, <code><a href="#pre">pre</a></code>, <code><a
   href="#table">table</a></code>, or <code><a href="#ul">ul</a></code>
   elements, even though these elements are technically allowed inside
   <code><a href="#p">p</a></code> elements according to the content models
   described in this specification. (In fact, if one of those elements is put
   inside a <code><a href="#p">p</a></code> element in the markup, it will
   instead imply a <code><a href="#p">p</a></code> element end tag before
   it.)

  <p>An <code>optgroup</code> element must not contain <code>optgroup</code>
   elements, even though these elements are technically allowed to be nested
   according to the content models described in this specification. (If an
   <code>optgroup</code> element is put inside another in the markup, it will
   in fact imply an <code>optgroup</code> end tag before it.)

  <p>A <code><a href="#table">table</a></code> element must not contain
   <code><a href="#tr">tr</a></code> elements, even though these elements are
   technically allowed inside <code><a href="#table">table</a></code>
   elements according to the content models described in this specification.
   (If a <code><a href="#tr">tr</a></code> element is put inside a <code><a
   href="#table">table</a></code> in the markup, it will in fact imply a
   <code><a href="#tbody">tbody</a></code> start tag before it.)

  <p>A single U+000A LINE FEED (LF) character may be placed immediately after
   the <span title=syntax-start-tag>start tag</span> of <code><a
   href="#pre">pre</a></code> and <code>textarea</code> elements. This does
   not affect the processing of the element. The otherwise optional U+000A
   LINE FEED (LF) character <em>must</em> be included if the element's
   contents start with that character (because otherwise the leading newline
   in the contents would be treated like the optional newline, and ignored).

  <div class=example>
   <p>The following two <code><a href="#pre">pre</a></code> blocks are
    equivalent:</p>

   <pre>&lt;pre>Hello&lt;/pre></pre>

   <pre>&lt;pre><br>Hello&lt;/pre></pre>
  </div>

  <h4 id=text><span class=secno>8.1.3. </span>Text</h4>

  <p><dfn id=text1 title=syntax-text>Text</dfn> is allowed inside elements,
   attributes, and comments. Text must consist of valid Unicode characters
   other than U+0000. Text should not contain control characters other than
   <a href="#space" title="space character">space characters</a>. Extra
   constraints are placed on what is and what is not allowed in text based on
   where the text is to be put, as described in the other sections.

  <h5 id=newlines><span class=secno>8.1.3.1. </span>Newlines</h5>

  <p><dfn id=newlines0 title=syntax-newlines>Newlines</dfn> in HTML may be
   represented either as U+000D CARRIAGE RETURN (CR) characters, U+000A LINE
   FEED (LF) characters, or pairs of U+000D CARRIAGE RETURN (CR), U+000A LINE
   FEED (LF) characters in that order.

  <h4 id=character><span class=secno>8.1.4. </span>Character entity
   references</h4>

  <p>In certain cases described in other sections, <a href="#text1"
   title=syntax-text>text</a> may be mixed with <dfn id=character0
   title=syntax-entities>character entity references</dfn>. These can be used
   to escape characters that couldn't otherwise legally be included in <a
   href="#text1" title=syntax-text>text</a>.

  <p>Character entity references must start with a U+0026 AMPERSAND
   (<code>&amp;</code>). Following this, there are three possible kinds of
   character entity references:

  <dl>
   <dt>Named entities

   <dd>The ampersand must be followed by one of the names given in the <a
    href="#entities0">entities</a> section, using the same case. Finally,
    after the name, the entity must be terminated by a U+003B SEMICOLON
    character (<code title="">;</code>).

   <dt>Decimal numeric entities

   <dd>The ampersand must be followed by a U+0023 NUMBER SIGN
    (<code>#</code>) character, followed by one or more digits in the range
    U+0030 DIGIT ZERO .. U+0039 DIGIT NINE, representing a base-ten integer
    that itself is a valid Unicode code point that is neither U+0000 nor a
    character in the range U+0080 .. U+009F. The digits must then be followed
    by a U+003B SEMICOLON character (<code title="">;</code>).

   <dt>Hexadecimal numeric entities

   <dd>The ampersand must be followed by a U+0023 NUMBER SIGN
    (<code>#</code>) character, which must be followed by either a U+0078
    LATIN SMALL LETTER X or a U+0058 LATIN CAPITAL LETTER X character, which
    must then be followed by one or more digits in the range U+0030 DIGIT
    ZERO .. U+0039 DIGIT NINE, U+0061 LATIN SMALL LETTER A .. U+0066 LATIN
    SMALL LETTER F, and U+0041 LATIN CAPITAL LETTER A .. U+0046 LATIN CAPITAL
    LETTER F, representing a base-sixteen integer that itself is a valid
    Unicode code point that is neither U+0000 nor a character in the range
    U+0080 .. U+009F. The digits must then be followed by a U+003B SEMICOLON
    character (<code title="">;</code>).
  </dl>

  <h4 id=comments><span class=secno>8.1.5. </span>Comments</h4>

  <p><dfn id=comments0 title=syntax-comments>Comments</dfn> must start with
   the four character sequence U+003C LESS-THAN SIGN, U+0021 EXCLAMATION
   MARK, U+002D HYPHEN-MINUS, U+002D HYPHEN-MINUS (<code
   title="">&lt;!--</code>). Following this sequence, the comment may have <a
   href="#text1" title=syntax-text>text</a>, with the additional restriction
   that the text must not contain two consecutive U+002D HYPHEN-MINUS (<code
   title="">-</code>) characters, nor end with a U+002D HYPHEN-MINUS (<code
   title="">-</code>) character. Finally, the comment must be ended by the
   three character sequence U+002D HYPHEN-MINUS, U+002D HYPHEN-MINUS, U+003E
   GREATER-THAN SIGN (<code title="">--&gt;</code>).

  <h3 id=parsing><span class=secno>8.2. </span>Parsing HTML documents</h3>

  <p><em>This section only applies to user agents, data mining tools, and
   conformance checkers.</em>

  <p>The rules for parsing <a href="#xml-documents">XML documents</a> (and
   thus <a href="#xhtml5">XHTML</a> documents) into DOM trees are covered by
   the XML and Namespaces in XML specifications, and are out of scope of this
   specification. <a href="#refsXML">[XML]</a> <a
   href="#refsXMLNS">[XMLNS]</a> <!-- XXX refs -->

  <p>For <a href="#html-">HTML documents</a>, user agents must use the
   parsing rules described in this section to generate the DOM trees.
   Together, these rules define what is referred to as the <dfn
   id=html-0>HTML parser</dfn>.</p>
  <!-- XXX should probably remove that "must" since
  it'll be redundant with something in the navigating processing model
  eventually -->

  <div class=note>
   <p>While the HTML form of HTML5 bears a close resemblance to SGML and XML,
    it is a separate language with its own parsing rules.</p>

   <p>Some earlier versions of HTML (in particular from HTML2 to HTML4) were
    based on SGML and used SGML parsing rules. However, few (if any) web
    browsers ever implemented true SGML parsing for HTML documents; the only
    user agents to strictly handle HTML as an SGML application have
    historically been validators. The resulting confusion &mdash; with
    validators claiming documents to have one representation while widely
    deployed Web browsers interoperably implemented a different
    representation &mdash; has wasted decades of productivity. This version
    of HTML thus returns to a non-SGML basis.</p>

   <p>Authors interested in using SGML tools in their authoring pipeline are
    encouraged to use XML tools and the XML serialisation of HTML5.</p>
  </div>

  <p>This specification defines the parsing rules for HTML documents, whether
   they are syntactically valid or not. Certain points in the parsing
   algorithm are said to be <dfn id=parse title="parse error">parse
   errors</dfn>. The error handling for parse errors is well-defined: user
   agents must either act as described below when encountering such problems,
   or must abort processing at the first error that they encounter for which
   they do not wish to apply the rules described below.

  <p>Conformance checkers must report at least one parse error condition to
   the user if one or more parse error conditions exist in the document and
   must not report parse error conditions if none exist in the document.
   Conformance checkers may report more than one parse error condition if
   more than one parse error conditions exist in the document. Conformance
   checkers are not required to recover from parse errors.

  <p class=note>Parse errors are only errors with the <em>syntax</em> of
   HTML. In addition to checking for parse errors, conformance checkers will
   also verify that the document obeys all the other conformance requirements
   described in this specification.

  <h4 id=overview><span class=secno>8.2.1. </span>Overview of the parsing
   model</h4>

  <p>The input to the HTML parsing process consists of a stream of Unicode
   characters, which is passed through a <a
   href="#tokenisation0">tokenisation</a> stage (lexical analysis) followed
   by a <a href="#tree-construction0">tree construction</a> stage (semantic
   analysis). The output is a <code>Document</code> object.

  <p class=note>Implementations that <a href="#non-scripted">do not support
   scripting</a> do not have to actually create a DOM <code>Document</code>
   object, but the DOM tree in such cases is still used as the model for the
   rest of the specification.

  <p>In the common case, the data handled by the tokenisation stage comes
   from the network, but <a href="#dynamic2" title="dynamic markup
   insertion">it can also come from script</a>, e.g. using the <code
   title=dom-document-write-HTML><a
   href="#document.write0">document.write()</a></code> API.

  <p><img alt="" src="images/parsing-model-overview.png">

  <p id=nestedParsing>There is only one set of state for the tokeniser stage
   and the tree construction stage, but the tree construction stage is
   reentrant, meaning that while the tree construction stage is handling one
   token, the tokeniser might be resumed, causing further tokens to be
   emitted and processed before the first token's processing is complete.

  <div class=example>
   <p>In the following example, the tree construction stage will be called
    upon to handle a "p" start tag token while handling the "script" start
    tag token:</p>

   <pre>...
&lt;script>
 document.write('&lt;p>');
&lt;/script>
...</pre>
  </div>

  <h4 id=the-input0><span class=secno>8.2.2. </span>The <dfn id=input0>input
   stream</dfn></h4>

  <p>The stream of Unicode characters that consists the input to the
   tokenisation stage will be initially seen by the user agent as a stream of
   bytes (typically coming over the network or from the local file system).
   The bytes encode the actual characters according to a particular
   <em>character encoding</em>, which the user agent must use to decode the
   bytes into characters.

  <p id=documentEncoding>For HTML, user agents must use the following
   algorithm in determining the character encoding of a document:

  <ol>
   <li>
    <p>If the transport layer specifies an encoding, use that, and abort
     these steps.

   <li>
    <p>The user agent may wait for 512 or more bytes of the resource to be
     available.

   <li>
    <p>Let <var title="">n</var> be the smaller of either 512 or the number
     of bytes already available.

   <li>
    <p>For each of the rows in the following table, starting with the first
     one and going down, if <var title="">n</var> is equal to or greater than
     the number of bytes in the first column, and the first bytes of the file
     match the bytes given in the first column, then use the encoding given
     in the cell in the second column of that row, and abort these steps:</p>

    <table>
     <thead>
      <tr>
       <th>Bytes in Hexadecimal

       <th>Description

     <tbody>
      <tr>
       <td>00 00 FE FF

       <td>UTF-32BE BOM

      <tr>
       <td>FF FE 00 00

       <td>UTF-32LE BOM

      <tr>
       <td>FE FF

       <td>UTF-16BE BOM

      <tr>
       <td>FF FE

       <td>UTF-16LE BOM

      <tr>
       <td>EF BB BF

       <td>UTF-8 BOM <!-- nobody uses this
      <tr>
       <td>DD 73 66 73
       <td>UTF-EBCDIC
-->
        
    </table>

   <li>
    <p>Otherwise, the user agent will have to search for explicit character
     encoding information in the file itself. This must proceed as follows:

    <p>Let <var title="">position</var> be a pointer to a byte in the input
     stream, initially pointing at the first byte. If at any point during
     these steps the <var title="">position</var> pointer points beyond the
     <var title="">n</var>th byte of the input stream, then skip to the next
     step of the overall character encoding detection algorithm (the step
     which mentions frequency analysis below).</p>

    <p>Now, repeat the following "two" steps until the algorithm aborts
     (either because <var title="">position</var> reaches beyond the <var
     title="">n</var>th byte, or because a character encoding is found):</p>

    <ol>
     <li>
      <p>If <var title="">position</var> points to:</p>

      <dl class=switch>
       <dt>A sequence of bytes starting with: 0x3C 0x21 0x2D 0x2D (ASCII
        '&lt;!--')

       <dd>
        <p>Advance the <var title="">position</var> pointer so that it points
         at the first 0x3E byte which is preceeded by two 0x2D bytes (i.e. at
         the end of an ASCII '-->' sequence) and comes after the second 0x2D
         byte that was found. (The two 0x2D bytes cannot be the same as the
         those in the '&lt;!--' sequence.) If no such byte is found before
         the <var title="">n</var>th byte, abort this "two step" algorithm.</p>

       <dt>A sequence of bytes starting with: 0x3C, 0x4D or 0x6D, 0x45 or
        0x65, 0x54 or 0x74, 0x41 or 0x61, and finally one of 0x09, 0x0A,
        0x0B, 0x0C, 0x0D, 0x20 (case-insensitive ASCII '&lt;meta' followed by
        a space)

       <dd>
        <ol>
         <li>
          <p>Advance the <var title="">position</var> pointer so that it
           points at the next 0x09, 0x0A, 0x0B, 0x0C, 0x0D, or 0x20 byte (the
           one in sequence of characters matched above), if there is one
           before the <var title="">n</var>th byte. If there isn't, abort the
           "two step" algorithm.

         <li>
          <p><a href="#get-an" title=concept-get-attributes-when-sniffing>Get
           an attribute</a> and its value. If no attribute was sniffed, then
           skip this inner set of steps, and jump to the second step in the
           overall "two step" algorithm.</p>

          <p class=note>As required above, if the <var
           title="">position</var> pointer points beyond the <var
           title="">n</var>th byte after the "get an attribute" step, the
           "two step" algorithm will abort.

         <li>
          <p>Examine the attribute's name:</p>

          <dl class=switch>
           <dt>If it is 'charset'

           <dd>
            <p>If the attribute's value is a supported character encoding,
             then use the given encoding, and abort all these steps.
             Otherwise, do nothing with this attribute.

           <dt>If it is 'content'

           <dd>
            <p>The attribute's value is now parsed.</p>

            <ol>
             <li>
              <p>Skip characters in the attribute's value up to and including
               the first U+003B SEMICOLON (<code title="">;</code>)
               character.

             <li>
              <p>Skip any U+0009, U+000A, U+000B, U+000C, U+000D, or U+0020
               characters (i.e. spaces) that immediately follow the
               semicolon.

             <li>
              <p>If the next six characters are not 'charset', abort this
               very inner set of steps (parsing the attribute's value), and
               continue looking for other attributes.

             <li>
              <p>Skip any U+0009, U+000A, U+000B, U+000C, U+000D, or U+0020
               characters that immediately follow the word 'charset' (there
               might not be any).

             <li>
              <p>If the next character is not a U+003D EQUALS SIGN ('='),
               abort this very inner set of steps (parsing the attribute's
               value), and continue looking for other attributes.

             <li>
              <p>Skip any U+0009, U+000A, U+000B, U+000C, U+000D, or U+0020
               characters that immediately follow the word equals sign (there
               might not be any).

             <li>
              <p>Process the next character as follows:</p>

              <dl class=switch>
               <dt>If it is a U+0022 QUOTATION MARK ('"') and there is a
                later U+0022 QUOTATION MARK ('"') in the attribute's value

               <dd>
                <p>Let <var title="">tentative encoding</var> be the string
                 between the two quotation marks.

               <dt>If it is a U+0027 APOSTROPHE ("'") and there is a later
                U+0027 APOSTROPHE ("'") in the attribute's value

               <dd>
                <p>Let <var title="">tentative encoding</var> be the string
                 between the two apostrophes.

               <dt>If it is an unmatched U+0022 QUOTATION MARK ('"')

               <dt>If it is an unmatched U+0027 APOSTROPHE ("'")

               <dd>
                <p>There is no <var title="">tentative encoding</var>.

               <dt>Otherwise

               <dd>
                <p>Let <var title="">tentative encoding</var> be the string
                 from this character to the first U+0009, U+000A, U+000B,
                 U+000C, U+000D, or U+0020 character or the end of the
                 attribute's value, whichever comes first.
              </dl>

             <li>If there is a <var title="">tentative encoding</var> and it
              is the name of a supported character encoding, then use that
              encoding; abort all these steps.

             <li>Otherwise, skip this 'content' attribute and continue on
              with any other attributes.
            </ol>

           <dd>

           <dt>Any other name

           <dd>
            <p>Do nothing with that attribute.
          </dl>

         <li>
          <p>Return to step 1 in these inner steps.
        </ol>

       <dt>A sequence of bytes starting with a 0x3C byte (ASCII '&lt;'),
        optionally a 0x2F byte (ASCII '/'), and finally a byte in the range
        0x41-0x5A or 0x61-0x7A (an ASCII letter)

       <dd>
        <ol>
         <li>
          <p>Advance the <var title="">position</var> pointer so that it
           points at the next 0x09 (ASCII TAB), 0x0A (ASCII LF), 0x0B (ASCII
           VT), 0x0C (ASCII FF), 0x0D (ASCII CR), 0x20 (ASCII space), 0x3E
           (ASCII '>'), 0x3C (ASCII '<') byte, if there is one before the
           <var title="">n</var>th byte. If there isn't, abort the "two step"
           algorithm.

         <li>
          <p>If the pointer points to a 0x3C (ASCII '<') byte, then return to
           the first step in the overall "two step" algorithm.

         <li>
          <p>Repeatedly <a href="#get-an"
           title=concept-get-attributes-when-sniffing>get an attribute</a>
           until no further attributes can be found, then jump to the second
           step in the overall "two step" algorithm.
        </ol>

       <dt>A sequence of bytes starting with: 0x3C 0x2D (ASCII '&lt;!')

       <dt>A sequence of bytes starting with: 0x3C 0x2F (ASCII '&lt;/')

       <dt>A sequence of bytes starting with: 0x3C 0x3F (ASCII '&lt;?')

       <dd>
        <p>Advance the <var title="">position</var> pointer so that it points
         at the first 0x3E byte (ASCII '>') that comes after the 0x3C byte
         that was found. If no such byte is found before the <var
         title="">n</var>th byte, abort this "two step" algorithm.</p>

       <dt>Any other byte

       <dd>
        <p>Do nothing with that byte.</p>
      </dl>

     <li>Move <var title="">position</var> so it points at the next byte in
      the input stream, and return to the first step of this "two step"
      algorithm.
    </ol>

    <p>When the above "two step" algorithm says to <dfn id=get-an
     title=concept-get-attributes-when-sniffing>get an attribute</dfn>, it
     means doing this:</p>

    <ol>
     <li>
      <p>If the byte at <var title="">position</var> is one of 0x09 (ASCII
       TAB), 0x0A (ASCII LF), 0x0B (ASCII VT), 0x0C (ASCII FF), 0x0D (ASCII
       CR), 0x20 (ASCII space), or 0x2F (ASCII '/') then advance <var
       title="">position</var> to the next byte and start over.

     <li>
      <p>If the byte at <var title="">position</var> is 0x3C (ASCII '&lt;'),
       then move <var title="">position</var> back to the previous byte, and
       stop looking for an attribute. There isn't one.

     <li>
      <p>If the byte at <var title="">position</var> is 0x3E (ASCII '>'),
       then stop looking for an attribute. There isn't one.

     <li>
      <p>Otherwise, the byte at <var title="">position</var> is the start of
       the attribute name. Let <var title="">attribute name</var> and <var
       title="">attribute value</var> be the empty string.

     <li>
      <p><em>Attribute name</em>: Process the byte at <var
       title="">position</var> as follows:</p>

      <dl class=switch>
       <dt>If it is 0x3D (ASCII '='), and the <var title="">attribute
        name</var> is longer than the empty string

       <dd>Advance <var title="">position</var> to the next byte and jump to
        the step below labelled <em>value</em>.

       <dt>If it is 0x09 (ASCII TAB), 0x0A (ASCII LF), 0x0B (ASCII VT), 0x0C
        (ASCII FF), 0x0D (ASCII CR), or 0x20 (ASCII space)

       <dd>Jump to the step below labelled <em>spaces</em>.

       <dt>If it is 0x2F (ASCII '/'), 0x3C (ASCII '&lt;'), or 0x3E (ASCII
        '&gt;')

       <dd>Stop looking for an attribute. The attribute's name is the value
        of <var title="">attribute name</var>, its value is the empty string.

       <dt>If it is in the range 0x41 (ASCII 'A') to 0x5A (ASCII 'Z')

       <dd>Append the Unicode character with codepoint <span><var
        title="">b</var>+0x20</span> to <var title="">attribute name</var>
        (where <var title="">b</var> is the value of the byte at <var
        title="">position</var>).

       <dt>Anything else

       <dd>Append the Unicode character with the same codepoint as the value
        of the byte at <var title="">position</var>) to <var
        title="">attribute name</var>. (It doesn't actually matter how bytes
        outside the ASCII range are handled here, since only ASCII characters
        can contribute to the detection of a character encoding.)
      </dl>

     <li>
      <p>Advance <var title="">position</var> to the next byte and return to
       the previous step.

     <li>
      <p><em>Spaces.</em> If the byte at <var title="">position</var> is one
       of 0x09 (ASCII TAB), 0x0A (ASCII LF), 0x0B (ASCII VT), 0x0C (ASCII
       FF), 0x0D (ASCII CR), or 0x20 (ASCII space) then advance <var
       title="">position</var> to the next byte, then, repeat this step.

     <li>
      <p>If the byte at <var title="">position</var> is <em>not</em> 0x3D
       (ASCII '='), stop looking for an attribute. Move <var
       title="">position</var> back to the previous byte. The attribute's
       name is the value of <var title="">attribute name</var>, its value is
       the empty string.

     <li>
      <p>Advance <var title="">position</var> past the 0x3D (ASCII '=') byte.

     <li>
      <p><em>Value.</em> If the byte at <var title="">position</var> is one
       of 0x09 (ASCII TAB), 0x0A (ASCII LF), 0x0B (ASCII VT), 0x0C (ASCII
       FF), 0x0D (ASCII CR), or 0x20 (ASCII space) then advance <var
       title="">position</var> to the next byte, then, repeat this step.

     <li>
      <p>Process the byte at <var title="">position</var> as follows:</p>

      <dl class=switch>
       <dt>If it is 0x22 (ASCII '"') or 0x27 ("'")

       <dd>
        <ol>
         <li>Let <var title="">b</var> be the value of the byte at <var
          title="">position</var>.

         <li>Advance <var title="">position</var> to the next byte.

         <li>If the value of the byte at <var title="">position</var> is the
          value of <var title="">b</var>, then stop looking for an attribute.
          The attribute's name is the value of <var title="">attribute
          name</var>, and its value is the value of <var title="">attribute
          value</var>.

         <li>Otherwise, if the value of the byte at <var
          title="">position</var> is in the range 0x41 (ASCII 'A') to 0x5A
          (ASCII 'Z'), then append a Unicode character to <var
          title="">attribute value</var> whose codepoint is 0x20 more than
          the value of the byte at <var title="">position</var>.

         <li>Otherwise, append a Unicode character to <var title="">attribute
          value</var> whose codepoint is the same as the value of the byte at
          <var title="">position</var>.

         <li>Return to the second step in these substeps.
        </ol>

       <dt>If it is 0x3C (ASCII '&lt;'), or 0x3E (ASCII '&gt;')

       <dd>Stop looking for an attribute. The attribute's name is the value
        of <var title="">attribute name</var>, its value is the empty string.

       <dt>If it is in the range 0x41 (ASCII 'A') to 0x5A (ASCII 'Z')

       <dd>Append the Unicode character with codepoint <span><var
        title="">b</var>+0x20</span> to <var title="">attribute value</var>
        (where <var title="">b</var> is the value of the byte at <var
        title="">position</var>).

       <dt>Anything else

       <dd>Append the Unicode character with the same codepoint as the value
        of the byte at <var title="">position</var>) to <var
        title="">attribute value</var>.
      </dl>

     <li>
      <p>Process the byte at <var title="">position</var> as follows:</p>

      <dl class=switch>
       <dt>If it is 0x09 (ASCII TAB), 0x0A (ASCII LF), 0x0B (ASCII VT), 0x0C
        (ASCII FF), 0x0D (ASCII CR), 0x20 (ASCII space), 0x3C (ASCII '&lt;'),
        or 0x3E (ASCII '&gt;')

       <dd>Stop looking for an attribute. The attribute's name is the value
        of <var title="">attribute name</var> and its value is the value of
        <var title="">attribute value</var>.

       <dt>If it is in the range 0x41 (ASCII 'A') to 0x5A (ASCII 'Z')

       <dd>Append the Unicode character with codepoint <span><var
        title="">b</var>+0x20</span> to <var title="">attribute value</var>
        (where <var title="">b</var> is the value of the byte at <var
        title="">position</var>).

       <dt>Anything else

       <dd>Append the Unicode character with the same codepoint as the value
        of the byte at <var title="">position</var>) to <var
        title="">attribute value</var>.
      </dl>

     <li>
      <p>Advance <var title="">position</var> to the next byte and return to
       the previous step.
    </ol>

   <li>
    <p>The user agent may attempt to autodetect the character encoding from
     applying frequency analysis or other algorithms to the data stream. If
     autodetection succeeds in determining a character encoding, then use
     that; abort these steps. <a href="#refsUNIVCHARDET">[UNIVCHARDET]</a>
   </li>
   <!--
   http://www.mozilla.org/projects/intl/UniversalCharsetDetection.html
   -->

   <li>
    <p>Otherwise, use an implementation-defined or user-specified default
     character encoding. Due to its use in legacy content, <code
     title="">windows-1252</code> is recommended as a default in
     predominantly Western demographics. In non-legacy environments, the more
     comprehensive <code title="">UTF-8</code> encoding is recommended
     instead. Since these encodings can in many cases be distinguished by
     inspection, a user agent may heuristically decide which to use as a
     default.
  </ol>

  <p class=note>For XML documents, the algorithm user agents must use to
   determine the character encoding is given by the XML specification. This
   section does not apply to XML documents. <a href="#refsXML">[XML]</a>

  <p>When a user agent would otherwise use the ISO-8859-1 encoding, it must
   instead use the Windows-1252 encoding. User agents must not support the
   CESU-8, UTF-7, BOCU-1 and SCSU encodings. <a href="#refsCESU8">[CESU8]</a>
   <a href="#refsUTF7">[UTF7]</a> <a href="#refsBOCU1">[BOCU1]</a> <a
   href="#refsSCSU">[SCSU]</a>

  <p>Bytes or sequences of bytes in the original byte stream that could not
   be converted to Unicode characters must be converted to U+FFFD REPLACEMENT
   CHARACTER code points.

  <p>A leading U+FEFF BYTE ORDER MARK (BOM) must be dropped if present.

  <p>All U+0000 NULL characters in the input must be replaced by U+FFFD
   REPLACEMENT CHARACTERs. Any occurrences of such characters is a <a
   href="#parse">parse error</a>.

  <p>U+000D CARRIAGE RETURN (CR) characters, and U+000A LINE FEED (LF)
   characters, are treated specially. Any CR characters that are followed by
   LF characters must be removed, and any CR characters not followed by LF
   characters must be converted to LF characters. Thus, newlines in HTML DOMs
   are represented by LF characters, and there are never any CR characters in
   the input to the <a href="#tokenisation0">tokenisation</a> stage.

  <p>The <dfn id=next-input>next input character</dfn> is the first character
   in the input stream that has not yet been <dfn id=consumed>consumed</dfn>.
   Initially, the <em><a href="#next-input">next input character</a></em> is
   the first character in the input.

  <p>The <dfn id=insertion>insertion point</dfn> is the position (just before
   a character or just before the end of the input stream) where content
   inserted using <code title=dom-document-write-HTML><a
   href="#document.write0">document.write()</a></code> is actually inserted.
   The insertion point is relative to the position of the character
   immediately after it, it is not an absolute offset into the input stream.
   Initially, the insertion point is uninitialised.

  <p>The "EOF" character in the tables below is a conceptual character
   representing the end of the <a href="#input0">input stream</a>. If the
   parser is a <a href="#script-created">script-created parser</a>, then the
   end of the <a href="#input0">input stream</a> is reached when an <dfn
   id=explicit>explicit "EOF" character</dfn> (inserted by the <code
   title=dom-document-close><a href="#close">document.close()</a></code>
   method) is consumed. Otherwise, the "EOF" character is not a real
   character in the stream, but rather the lack of any further characters.

  <h4 id=tokenisation><span class=secno>8.2.3. </span><dfn
   id=tokenisation0>Tokenisation</dfn></h4>

  <p>Implementations must act as if they used the following state machine to
   tokenise HTML. The state machine must start in the <a
   href="#data-state">data state</a>. Most states consume a single character,
   which may have various side-effects, and either switches the state machine
   to a new state to <em>reconsume</em> the same character, or switches it to
   a new state (to consume the next character), or repeats the same state (to
   consume the next character). Some states have more complicated behaviour
   and can consume several characters before switching to another state.

  <p>The exact behaviour of certain states depends on a <dfn
   id=content2>content model flag</dfn> that is set after certain tokens are
   emitted. The flag has several states: <em title="">PCDATA</em>, <em
   title="">RCDATA</em>, <em title="">CDATA</em>, and <em
   title="">PLAINTEXT</em>. Initially it must be in the PCDATA state. In the
   RCDATA and CDATA states, a further <dfn id=escape>escape flag</dfn> is
   used to control the behaviour of the tokeniser. It is either true or
   false, and initially must be set to the false state.

  <p>The output of the tokenisation step is a series of zero or more of the
   following tokens: DOCTYPE, start tag, end tag, comment, character,
   end-of-file. DOCTYPE tokens have names and can be either correct or in
   error. Start and end tag tokens have a tag name and a list of attributes,
   each of which has a name and a value. Comment and character tokens have
   data.

  <p>When a token is emitted, it must immediately be handled by the <a
   href="#tree-construction0">tree construction</a> stage. The tree
   construction stage can affect the state of the <a href="#content2">content
   model flag</a>, and can insert additional characters into the stream. (For
   example, the <code><a href="#script0">script</a></code> element can result
   in scripts executing and using the <a href="#dynamic2">dynamic markup
   insertion</a> APIs to insert characters into the stream being tokenised.)

  <p>When an end tag token is emitted, the <a href="#content2">content model
   flag</a> must be switched to the PCDATA state.

  <p>When an end tag token is emitted with attributes, that is a <a
   href="#parse">parse error</a>.

  <p>Before each step of the tokeniser, the user agent may check to see if
   either one of the scripts in the <a href="#list-of1">list of scripts that
   will execute as soon as possible</a> or the first script in the <a
   href="#list-of0">list of scripts that will execute asynchronously</a>, has
   <span>completed loading</span><!-- XXX xref -->. If one has, then it must
   be <a href="#executing0" title="executing a script block">executed</a> and
   removed from its list.

  <p>The tokeniser state machine is as follows:

  <dl>
   <dt><dfn id=data-state>Data state</dfn>

   <dd>
    <p>Consume the <a href="#next-input">next input character</a>:</p>

    <dl class=switch>
     <dt>U+0026 AMPERSAND (&amp;)

     <dd>When the <a href="#content2">content model flag</a> is set to one of
      the PCDATA or RCDATA states: switch to the <a href="#entity">entity
      data state</a>.

     <dd>Otherwise: treat it as per the "anything else" entry below.

     <dt>U+002D HYPHEN-MINUS (-)

     <dd>
      <p>If the <a href="#content2">content model flag</a> is set to either
       the RCDATA state or the CDATA state, and the <a href="#escape">escape
       flag</a> is false, and there are at least three characters before this
       one in the input stream, and the last four characters in the input
       stream, including this one, are U+003C LESS-THAN SIGN, U+0021
       EXCLAMATION MARK, U+002D HYPHEN-MINUS, and U+002D HYPHEN-MINUS
       ("&lt;!--"), then set the <a href="#escape">escape flag</a> to true.</p>

      <p>In any case, emit the input character as a character token. Stay in
       the <a href="#data-state">data state</a>.</p>

     <dt>U+003C LESS-THAN SIGN (&lt;)

     <dd>When the <a href="#content2">content model flag</a> is set to the
      PCDATA state: switch to the <a href="#tag-open">tag open state</a>.

     <dd>When the <a href="#content2">content model flag</a> is set to either
      the RCDATA state or the CDATA state and the <a href="#escape">escape
      flag</a> is false: switch to the <a href="#tag-open">tag open
      state</a>.

     <dd>Otherwise: treat it as per the "anything else" entry below.

     <dt>U+003E GREATER-THAN SIGN (&gt;)

     <dd>
      <p>If the <a href="#content2">content model flag</a> is set to either
       the RCDATA state or the CDATA state, and the <a href="#escape">escape
       flag</a> is true, and the last three characters in the input stream
       including this one are U+002D HYPHEN-MINUS, U+002D HYPHEN-MINUS,
       U+003E GREATER-THAN SIGN ("--&gt;"), set the <a href="#escape">escape
       flag</a> to false.</p>
      <!-- no need to check
      that there are enough characters, since you can only run into
      this if the flag is true in the first place, which requires four
      characters. -->
      
      <p>In any case, emit the input character as a character token. Stay in
       the <a href="#data-state">data state</a>.</p>

     <dt>EOF

     <dd>Emit an end-of-file token.

     <dt>Anything else

     <dd>Emit the input character as a character token. Stay in the <a
      href="#data-state">data state</a>.
    </dl>

   <dt><dfn id=entity>Entity data state</dfn>

   <dd>
    <p><em>(This cannot happen if the <a href="#content2">content model
     flag</a> is set to the CDATA state.)</em></p>

    <p>Attempt to <a href="#consume">consume an entity</a>.</p>

    <p>If nothing is returned, emit a U+0026 AMPERSAND character token.</p>

    <p>Otherwise, emit the character token that was returned.</p>

    <p>Finally, switch to the <a href="#data-state">data state</a>.</p>

   <dt><dfn id=tag-open>Tag open state</dfn>

   <dd>
    <p>The behaviour of this state depends on the <a href="#content2">content
     model flag</a>.</p>

    <dl>
     <dt>If the <a href="#content2">content model flag</a> is set to the
      RCDATA or CDATA states

     <dd>
      <p>If the <a href="#next-input">next input character</a> is a U+002F
       SOLIDUS (/) character, consume it and switch to the <a
       href="#close1">close tag open state</a>. If the <a
       href="#next-input">next input character</a> is not a U+002F SOLIDUS
       (/) character, emit a U+003C LESS-THAN SIGN character token and switch
       to the <a href="#data-state">data state</a> to process the <a
       href="#next-input">next input character</a>.</p>

     <dt>If the <a href="#content2">content model flag</a> is set to the
      PCDATA state

     <dd>
      <p>Consume the <a href="#next-input">next input character</a>:</p>

      <dl class=switch>
       <dt>U+0021 EXCLAMATION MARK (!)

       <dd>Switch to the <a href="#markup">markup declaration open state</a>.

       <dt>U+002F SOLIDUS (/)

       <dd>Switch to the <a href="#close1">close tag open state</a>.

       <dt>U+0041 LATIN CAPITAL LETTER A through to U+005A LATIN CAPITAL
        LETTER Z

       <dd>Create a new start tag token, set its tag name to the lowercase
        version of the input character (add 0x0020 to the character's code
        point), then switch to the <a href="#tag-name0">tag name state</a>.
        (Don't emit the token yet; further details will be filled in before
        it is emitted.)

       <dt>U+0061 LATIN SMALL LETTER A through to U+007A LATIN SMALL LETTER Z

       <dd>Create a new start tag token, set its tag name to the input
        character, then switch to the <a href="#tag-name0">tag name
        state</a>. (Don't emit the token yet; further details will be filled
        in before it is emitted.)

       <dt>U+003E GREATER-THAN SIGN (&gt;)

       <dd><a href="#parse">Parse error</a>. Emit a U+003C LESS-THAN SIGN
        character token and a U+003E GREATER-THAN SIGN character token.
        Switch to the <a href="#data-state">data state</a>.

       <dt>U+003F QUESTION MARK (?)

       <dd><a href="#parse">Parse error</a>. Switch to the <a
        href="#bogus">bogus comment state</a>.

       <dt>Anything else

       <dd><a href="#parse">Parse error</a>. Emit a U+003C LESS-THAN SIGN
        character token and reconsume the current input character in the <a
        href="#data-state">data state</a>.
      </dl>
    </dl>

   <dt><dfn id=close1>Close tag open state</dfn>

   <dd>
    <p>If the <a href="#content2">content model flag</a> is set to the RCDATA
     or CDATA states then examine the next few characters. If they do not
     match the tag name of the last start tag token emitted (case
     insensitively), or if they do but they are not immediately followed by
     one of the following characters:</p>

    <ul class=brief>
     <li>U+0009 CHARACTER TABULATION

     <li>U+000A LINE FEED (LF)

     <li>U+000B LINE TABULATION

     <li>U+000C FORM FEED (FF)</li>
     <!--<li>U+000D CARRIAGE RETURN (CR)</li>-->

     <li>U+0020 SPACE

     <li>U+003E GREATER-THAN SIGN (&gt;)

     <li>U+002F SOLIDUS (/)

     <li>U+003C LESS-THAN SIGN (&lt;)

     <li>EOF
    </ul>

    <p>...then there is a <a href="#parse">parse error</a>. Emit a U+003C
     LESS-THAN SIGN character token, a U+002F SOLIDUS character token, and
     switch to the <a href="#data-state">data state</a> to process the <a
     href="#next-input">next input character</a>.</p>

    <p>Otherwise, if the <a href="#content2">content model flag</a> is set to
     the PCDATA state, or if the next few characters <em>do</em> match that
     tag name, consume the <a href="#next-input">next input character</a>:</p>

    <dl class=switch>
     <dt>U+0041 LATIN CAPITAL LETTER A through to U+005A LATIN CAPITAL LETTER
      Z

     <dd>Create a new end tag token, set its tag name to the lowercase
      version of the input character (add 0x0020 to the character's code
      point), then switch to the <a href="#tag-name0">tag name state</a>.
      (Don't emit the token yet; further details will be filled in before it
      is emitted.)

     <dt>U+0061 LATIN SMALL LETTER A through to U+007A LATIN SMALL LETTER Z

     <dd>Create a new end tag token, set its tag name to the input character,
      then switch to the <a href="#tag-name0">tag name state</a>. (Don't emit
      the token yet; further details will be filled in before it is emitted.)

     <dt>U+003E GREATER-THAN SIGN (&gt;)

     <dd><a href="#parse">Parse error</a>. Switch to the <a
      href="#data-state">data state</a>.

     <dt>EOF

     <dd><a href="#parse">Parse error</a>. Emit a U+003C LESS-THAN SIGN
      character token and a U+002F SOLIDUS character token. Reconsume the EOF
      character in the <a href="#data-state">data state</a>.

     <dt>Anything else

     <dd><a href="#parse">Parse error</a>. Switch to the <a
      href="#bogus">bogus comment state</a>.
    </dl>

   <dt><dfn id=tag-name0>Tag name state</dfn>

   <dd>
    <p>Consume the <a href="#next-input">next input character</a>:</p>

    <dl class=switch>
     <dt>U+0009 CHARACTER TABULATION

     <dt>U+000A LINE FEED (LF)

     <dt>U+000B LINE TABULATION

     <dt>U+000C FORM FEED (FF)</dt>
     <!--<dt>U+000D CARRIAGE RETURN (CR)</dt>-->

     <dt>U+0020 SPACE

     <dd>Switch to the <a href="#before">before attribute name state</a>.

     <dt>U+003E GREATER-THAN SIGN (&gt;)

     <dd>Emit the current tag token. Switch to the <a href="#data-state">data
      state</a>.

     <dt>U+0041 LATIN CAPITAL LETTER A through to U+005A LATIN CAPITAL LETTER
      Z

     <dd>Append the lowercase version of the current input character (add
      0x0020 to the character's code point) to the current tag token's tag
      name. Stay in the <a href="#tag-name0">tag name state</a>.

     <dt>U+003C LESS-THAN SIGN (&lt;)

     <dt>EOF

     <dd><a href="#parse">Parse error</a>. Emit the current tag token.
      Reconsume the character in the <a href="#data-state">data state</a>.

     <dt>U+002F SOLIDUS (/)

     <dd><a href="#parse">Parse error</a> unless this is a <a
      href="#permitted">permitted slash</a>. Switch to the <a
      href="#before">before attribute name state</a>.

     <dt>Anything else

     <dd>Append the current input character to the current tag token's tag
      name. Stay in the <a href="#tag-name0">tag name state</a>.
    </dl>

   <dt><dfn id=before>Before attribute name state</dfn>

   <dd>
    <p>Consume the <a href="#next-input">next input character</a>:</p>

    <dl class=switch>
     <dt>U+0009 CHARACTER TABULATION

     <dt>U+000A LINE FEED (LF)

     <dt>U+000B LINE TABULATION

     <dt>U+000C FORM FEED (FF)</dt>
     <!--<dt>U+000D CARRIAGE RETURN (CR)</dt>-->

     <dt>U+0020 SPACE

     <dd>Stay in the <a href="#before">before attribute name state</a>.

     <dt>U+003E GREATER-THAN SIGN (&gt;)

     <dd>Emit the current tag token. Switch to the <a href="#data-state">data
      state</a>.

     <dt>U+0041 LATIN CAPITAL LETTER A through to U+005A LATIN CAPITAL LETTER
      Z

     <dd>Start a new attribute in the current tag token. Set that attribute's
      name to the lowercase version of the current input character (add
      0x0020 to the character's code point), and its value to the empty
      string. Switch to the <a href="#attribute1">attribute name state</a>.

     <dt>U+002F SOLIDUS (/)

     <dd><a href="#parse">Parse error</a> unless this is a <a
      href="#permitted">permitted slash</a>. Stay in the <a
      href="#before">before attribute name state</a>.

     <dt>U+003C LESS-THAN SIGN (&lt;)

     <dt>EOF

     <dd><a href="#parse">Parse error</a>. Emit the current tag token.
      Reconsume the character in the <a href="#data-state">data state</a>.

     <dt>Anything else

     <dd>Start a new attribute in the current tag token. Set that attribute's
      name to the current input character, and its value to the empty string.
      Switch to the <a href="#attribute1">attribute name state</a>.
    </dl>

   <dt><dfn id=attribute1>Attribute name state</dfn>

   <dd>
    <p>Consume the <a href="#next-input">next input character</a>:</p>

    <dl class=switch>
     <dt>U+0009 CHARACTER TABULATION

     <dt>U+000A LINE FEED (LF)

     <dt>U+000B LINE TABULATION

     <dt>U+000C FORM FEED (FF)</dt>
     <!--<dt>U+000D CARRIAGE RETURN (CR)</dt>-->

     <dt>U+0020 SPACE

     <dd>Switch to the <a href="#after">after attribute name state</a>.

     <dt>U+003D EQUALS SIGN (=)

     <dd>Switch to the <a href="#before0">before attribute value state</a>.

     <dt>U+003E GREATER-THAN SIGN (&gt;)

     <dd>Emit the current tag token. Switch to the <a href="#data-state">data
      state</a>.

     <dt>U+0041 LATIN CAPITAL LETTER A through to U+005A LATIN CAPITAL LETTER
      Z

     <dd>Append the lowercase version of the current input character (add
      0x0020 to the character's code point) to the current attribute's name.
      Stay in the <a href="#attribute1">attribute name state</a>.

     <dt>U+002F SOLIDUS (/)

     <dd><a href="#parse">Parse error</a> unless this is a <a
      href="#permitted">permitted slash</a>. Switch to the <a
      href="#before">before attribute name state</a>.

     <dt>U+003C LESS-THAN SIGN (&lt;)

     <dt>EOF

     <dd><a href="#parse">Parse error</a>. Emit the current tag token.
      Reconsume the character in the <a href="#data-state">data state</a>.

     <dt>Anything else

     <dd>Append the current input character to the current attribute's name.
      Stay in the <a href="#attribute1">attribute name state</a>.
    </dl>

    <p>When the user agent leaves the attribute name state (and before
     emitting the tag token, if appropriate), the complete attribute's name
     must be compared to the other attributes on the same token; if there is
     already an attribute on the token with the exact same name, then this is
     a <a href="#parse">parse error</a> and the new attribute must be
     dropped, along with the value that gets associated with it (if any).</p>

   <dt><dfn id=after>After attribute name state</dfn>

   <dd>
    <p>Consume the <a href="#next-input">next input character</a>:</p>

    <dl class=switch>
     <dt>U+0009 CHARACTER TABULATION

     <dt>U+000A LINE FEED (LF)

     <dt>U+000B LINE TABULATION

     <dt>U+000C FORM FEED (FF)</dt>
     <!--<dt>U+000D CARRIAGE RETURN (CR)</dt>-->

     <dt>U+0020 SPACE

     <dd>Stay in the <a href="#after">after attribute name state</a>.

     <dt>U+003D EQUALS SIGN (=)

     <dd>Switch to the <a href="#before0">before attribute value state</a>.

     <dt>U+003E GREATER-THAN SIGN (&gt;)

     <dd>Emit the current tag token. Switch to the <a href="#data-state">data
      state</a>.

     <dt>U+0041 LATIN CAPITAL LETTER A through to U+005A LATIN CAPITAL LETTER
      Z

     <dd>Start a new attribute in the current tag token. Set that attribute's
      name to the lowercase version of the current input character (add
      0x0020 to the character's code point), and its value to the empty
      string. Switch to the <a href="#attribute1">attribute name state</a>.

     <dt>U+002F SOLIDUS (/)

     <dd><a href="#parse">Parse error</a> unless this is a <a
      href="#permitted">permitted slash</a>. Switch to the <a
      href="#before">before attribute name state</a>.

     <dt>U+003C LESS-THAN SIGN (&lt;)

     <dt>EOF

     <dd><a href="#parse">Parse error</a>. Emit the current tag token.
      Reconsume the character in the <a href="#data-state">data state</a>.

     <dt>Anything else

     <dd>Start a new attribute in the current tag token. Set that attribute's
      name to the current input character, and its value to the empty string.
      Switch to the <a href="#attribute1">attribute name state</a>.
    </dl>

   <dt><dfn id=before0>Before attribute value state</dfn>

   <dd>
    <p>Consume the <a href="#next-input">next input character</a>:</p>

    <dl class=switch>
     <dt>U+0009 CHARACTER TABULATION

     <dt>U+000A LINE FEED (LF)

     <dt>U+000B LINE TABULATION

     <dt>U+000C FORM FEED (FF)</dt>
     <!--<dt>U+000D CARRIAGE RETURN (CR)</dt>-->

     <dt>U+0020 SPACE

     <dd>Stay in the <a href="#before0">before attribute value state</a>.

     <dt>U+0022 QUOTATION MARK (&quot;)

     <dd>Switch to the <a href="#attribute2">attribute value (double-quoted)
      state</a>.

     <dt>U+0026 AMPERSAND (&amp;)

     <dd>Switch to the <a href="#attribute4">attribute value (unquoted)
      state</a> and reconsume this input character.

     <dt>U+0027 APOSTROPHE (')

     <dd>Switch to the <a href="#attribute3">attribute value (single-quoted)
      state</a>.

     <dt>U+003E GREATER-THAN SIGN (&gt;)

     <dd>Emit the current tag token. Switch to the <a href="#data-state">data
      state</a>.

     <dt>U+003C LESS-THAN SIGN (&lt;)

     <dt>EOF

     <dd><a href="#parse">Parse error</a>. Emit the current tag token.
      Reconsume the character in the <a href="#data-state">data state</a>.

     <dt>Anything else

     <dd>Append the current input character to the current attribute's value.
      Switch to the <a href="#attribute4">attribute value (unquoted)
      state</a>.
    </dl>

   <dt><dfn id=attribute2>Attribute value (double-quoted) state</dfn>

   <dd>
    <p>Consume the <a href="#next-input">next input character</a>:</p>

    <dl class=switch>
     <dt>U+0022 QUOTATION MARK (&quot;)

     <dd>Switch to the <a href="#before">before attribute name state</a>.

     <dt>U+0026 AMPERSAND (&amp;)

     <dd>Switch to the <a href="#entity0">entity in attribute value
      state</a>.

     <dt>EOF

     <dd><a href="#parse">Parse error</a>. Emit the current tag token.
      Reconsume the character in the <a href="#data-state">data state</a>.

     <dt>Anything else

     <dd>Append the current input character to the current attribute's value.
      Stay in the <a href="#attribute2">attribute value (double-quoted)
      state</a>.
    </dl>

   <dt><dfn id=attribute3>Attribute value (single-quoted) state</dfn>

   <dd>
    <p>Consume the <a href="#next-input">next input character</a>:</p>

    <dl class=switch>
     <dt>U+0027 APOSTROPHE (')

     <dd>Switch to the <a href="#before">before attribute name state</a>.

     <dt>U+0026 AMPERSAND (&amp;)

     <dd>Switch to the <a href="#entity0">entity in attribute value
      state</a>.

     <dt>EOF

     <dd><a href="#parse">Parse error</a>. Emit the current tag token.
      Reconsume the character in the <a href="#data-state">data state</a>.

     <dt>Anything else

     <dd>Append the current input character to the current attribute's value.
      Stay in the <a href="#attribute3">attribute value (single-quoted)
      state</a>.
    </dl>

   <dt><dfn id=attribute4>Attribute value (unquoted) state</dfn>

   <dd>
    <p>Consume the <a href="#next-input">next input character</a>:</p>

    <dl class=switch>
     <dt>U+0009 CHARACTER TABULATION

     <dt>U+000A LINE FEED (LF)

     <dt>U+000B LINE TABULATION

     <dt>U+000C FORM FEED (FF)</dt>
     <!--<dt>U+000D CARRIAGE RETURN (CR)</dt>-->

     <dt>U+0020 SPACE

     <dd>Switch to the <a href="#before">before attribute name state</a>.

     <dt>U+0026 AMPERSAND (&amp;)

     <dd>Switch to the <a href="#entity0">entity in attribute value
      state</a>.

     <dt>U+003E GREATER-THAN SIGN (&gt;)

     <dd>Emit the current tag token. Switch to the <a href="#data-state">data
      state</a>.

     <dt>U+003C LESS-THAN SIGN (&lt;)

     <dt>EOF

     <dd><a href="#parse">Parse error</a>. Emit the current tag token.
      Reconsume the character in the <a href="#data-state">data state</a>.

     <dt>Anything else

     <dd>Append the current input character to the current attribute's value.
      Stay in the <a href="#attribute4">attribute value (unquoted) state</a>.
    </dl>

   <dt><dfn id=entity0>Entity in attribute value state</dfn>

   <dd>
    <p>Attempt to <a href="#consume">consume an entity</a>.</p>

    <p>If nothing is returned, append a U+0026 AMPERSAND character to the
     current attribute's value.</p>

    <p>Otherwise, append the returned character token to the current
     attribute's value.</p>

    <p>Finally, switch back to the attribute value state that you were in
     when were switched into this state.</p>

   <dt><dfn id=bogus>Bogus comment state</dfn>

   <dd>
    <p><em>(This can only happen if the <a href="#content2">content model
     flag</a> is set to the PCDATA state.)</em></p>

    <p>Consume every character up to the first U+003E GREATER-THAN SIGN
     character (&gt;) or the end of the file (EOF), whichever comes first.
     Emit a comment token whose data is the concatenation of all the
     characters starting from and including the character that caused the
     state machine to switch into the bogus comment state, up to and
     including the last consumed character before the U+003E character, if
     any, or up to the end of the file otherwise. (If the comment was started
     by the end of the file (EOF), the token is empty.)</p>

    <p>Switch to the <a href="#data-state">data state</a>.</p>

    <p>If the end of the file was reached, reconsume the EOF character.</p>

   <dt><dfn id=markup>Markup declaration open state</dfn>

   <dd>
    <p><em>(This can only happen if the <a href="#content2">content model
     flag</a> is set to the PCDATA state.)</em></p>

    <p>If the next two characters are both U+002D HYPHEN-MINUS (-)
     characters, consume those two characters, create a comment token whose
     data is the empty string, and switch to the <a href="#comment">comment
     state</a>.</p>

    <p>Otherwise if the next seven chacacters are a
     <span>case-insensitive</span><!-- XXX xref, ascii only --> match for the
     word "DOCTYPE", then consume those characters and switch to the <a
     href="#doctype0">DOCTYPE state</a>.</p>

    <p>Otherwise, is is a <a href="#parse">parse error</a>. Switch to the <a
     href="#bogus">bogus comment state</a>. The next character that is
     consumed, if any, is the first character that will be in the comment.</p>

   <dt><dfn id=comment>Comment state</dfn>

   <dd>
    <p>Consume the <a href="#next-input">next input character</a>:</p>

    <dl class=switch>
     <dt>U+002D HYPHEN-MINUS (-)

     <dd>Switch to the <a href="#comment0">comment dash state</a>

     <dt>EOF

     <dd><a href="#parse">Parse error</a>. Emit the comment token. Reconsume
      the EOF character in the <a href="#data-state">data state</a>.</dd>
     <!-- For
     security reasons: otherwise, hostile user could put a <script> in
     a comment e.g. in a blog comment and then DOS the server so that
     the end tag isn't read, and then the commented <script> tag would
     be treated as live code -->

     <dt>Anything else

     <dd>Append the input character to the comment token's data. Stay in the
      <a href="#comment">comment state</a>.
    </dl>

   <dt><dfn id=comment0>Comment dash state</dfn>

   <dd>
    <p>Consume the <a href="#next-input">next input character</a>:</p>

    <dl class=switch>
     <dt>U+002D HYPHEN-MINUS (-)

     <dd>Switch to the <a href="#comment1">comment end state</a>

     <dt>EOF

     <dd><a href="#parse">Parse error</a>. Emit the comment token. Reconsume
      the EOF character in the <a href="#data-state">data state</a>.</dd>
     <!-- For
     security reasons: otherwise, hostile user could put a <script> in
     a comment e.g. in a blog comment and then DOS the server so that
     the end tag isn't read, and then the commented <script> tag would
     be treated as live code -->

     <dt>Anything else

     <dd>Append a U+002D HYPHEN-MINUS (-) character and the input character
      to the comment token's data. Switch to the <a href="#comment">comment
      state</a>.
    </dl>

   <dt><dfn id=comment1>Comment end state</dfn>

   <dd>
    <p>Consume the <a href="#next-input">next input character</a>:</p>

    <dl class=switch>
     <dt>U+003E GREATER-THAN SIGN (&gt;)

     <dd>Emit the comment token. Switch to the <a href="#data-state">data
      state</a>.

     <dt>U+002D HYPHEN-MINUS (-)

     <dd><a href="#parse">Parse error</a>. Append a U+002D HYPHEN-MINUS (-)
      character to the comment token's data. Stay in the <a
      href="#comment1">comment end state</a>.

     <dt>EOF

     <dd><a href="#parse">Parse error</a>. Emit the comment token. Reconsume
      the EOF character in the <a href="#data-state">data state</a>.</dd>
     <!-- For
     security reasons: otherwise, hostile user could put a <script> in
     a comment e.g. in a blog comment and then DOS the server so that
     the end tag isn't read, and then the commented <script> tag would
     be treated as live code -->

     <dt>Anything else

     <dd><a href="#parse">Parse error</a>. Append two U+002D HYPHEN-MINUS (-)
      characters and the input character to the comment token's data. Switch
      to the <a href="#comment">comment state</a>.
    </dl>

   <dt><dfn id=doctype0>DOCTYPE state</dfn>

   <dd>
    <p>Consume the <a href="#next-input">next input character</a>:</p>

    <dl class=switch>
     <dt>U+0009 CHARACTER TABULATION

     <dt>U+000A LINE FEED (LF)

     <dt>U+000B LINE TABULATION

     <dt>U+000C FORM FEED (FF)</dt>
     <!--<dt>U+000D CARRIAGE RETURN (CR)</dt>-->

     <dt>U+0020 SPACE

     <dd>Switch to the <a href="#before1">before DOCTYPE name state</a>.

     <dt>Anything else

     <dd><a href="#parse">Parse error</a>. Reconsume the current character in
      the <a href="#before1">before DOCTYPE name state</a>.
    </dl>

   <dt><dfn id=before1>Before DOCTYPE name state</dfn>

   <dd>
    <p>Consume the <a href="#next-input">next input character</a>:</p>

    <dl class=switch>
     <dt>U+0009 CHARACTER TABULATION

     <dt>U+000A LINE FEED (LF)

     <dt>U+000B LINE TABULATION

     <dt>U+000C FORM FEED (FF)</dt>
     <!--<dt>U+000D CARRIAGE RETURN (CR)</dt>-->

     <dt>U+0020 SPACE

     <dd>Stay in the <a href="#before1">before DOCTYPE name state</a>.

     <dt>U+0061 LATIN SMALL LETTER A through to U+007A LATIN SMALL LETTER Z

     <dd>Create a new DOCTYPE token. Set the token's name name to the
      uppercase version of the current input character (subtract 0x0020 from
      the character's code point), and mark it as being in error. Switch to
      the <a href="#doctype1">DOCTYPE name state</a>.

     <dt>U+003E GREATER-THAN SIGN (&gt;)

     <dd><a href="#parse">Parse error</a>. Emit a DOCTYPE token whose name is
      the empty string and that is marked as being in error. Switch to the <a
      href="#data-state">data state</a>.

     <dt>EOF

     <dd><a href="#parse">Parse error</a>. Emit a DOCTYPE token whose name is
      the empty string and that is marked as being in error. Reconsume the
      EOF character in the <a href="#data-state">data state</a>.

     <dt>Anything else

     <dd>Create a new DOCTYPE token. Set the token's name name to the current
      input character, and mark it as being in error. Switch to the <a
      href="#doctype1">DOCTYPE name state</a>.
    </dl>

   <dt><dfn id=doctype1>DOCTYPE name state</dfn>

   <dd>
    <p>First, consume the <a href="#next-input">next input character</a>:</p>

    <dl class=switch>
     <dt>U+0009 CHARACTER TABULATION

     <dt>U+000A LINE FEED (LF)

     <dt>U+000B LINE TABULATION

     <dt>U+000C FORM FEED (FF)</dt>
     <!--<dt>U+000D CARRIAGE RETURN (CR)</dt>-->

     <dt>U+0020 SPACE

     <dd>Switch to the <a href="#after0">after DOCTYPE name state</a>.

     <dt>U+003E GREATER-THAN SIGN (&gt;)

     <dd>Emit the current DOCTYPE token. Switch to the <a
      href="#data-state">data state</a>.

     <dt>U+0061 LATIN SMALL LETTER A through to U+007A LATIN SMALL LETTER Z

     <dd>Append the uppercase version of the current input character
      (subtract 0x0020 from the character's code point) to the current
      DOCTYPE token's name. Stay in the <a href="#doctype1">DOCTYPE name
      state</a>.

     <dt>EOF

     <dd><a href="#parse">Parse error</a>. Emit the current DOCTYPE token.
      Reconsume the EOF character in the <a href="#data-state">data
      state</a>.

     <dt>Anything else

     <dd>Append the current input character to the current DOCTYPE token's
      name. Stay in the <a href="#doctype1">DOCTYPE name state</a>.
    </dl>

    <p>Then, if the name of the DOCTYPE token is exactly the four letters
     "HTML", then mark the token as being correct. Otherwise, mark it as
     being in error.</p>

    <p class=note>Because lowercase letters in the name are uppercased by the
     algorithm above, the "HTML" letters are actually case-insensitive
     relative to the markup.</p>

   <dt><dfn id=after0>After DOCTYPE name state</dfn>

   <dd>
    <p>Consume the <a href="#next-input">next input character</a>:</p>

    <dl class=switch>
     <dt>U+0009 CHARACTER TABULATION

     <dt>U+000A LINE FEED (LF)

     <dt>U+000B LINE TABULATION

     <dt>U+000C FORM FEED (FF)</dt>
     <!--<dt>U+000D CARRIAGE RETURN (CR)</dt>-->

     <dt>U+0020 SPACE

     <dd>Stay in the <a href="#after0">after DOCTYPE name state</a>.

     <dt>U+003E GREATER-THAN SIGN (&gt;)

     <dd>Emit the current DOCTYPE token. Switch to the <a
      href="#data-state">data state</a>.

     <dt>EOF

     <dd><a href="#parse">Parse error</a>. Emit the current DOCTYPE token.
      Reconsume the EOF character in the <a href="#data-state">data
      state</a>.

     <dt>Anything else

     <dd><a href="#parse">Parse error</a>. Mark the DOCTYPE token as being in
      error, if it is not already. Switch to the <a href="#bogus0">bogus
      DOCTYPE state</a>.
    </dl>

   <dt><dfn id=bogus0>Bogus DOCTYPE state</dfn>

   <dd>
    <p>Consume the <a href="#next-input">next input character</a>:</p>

    <dl class=switch>
     <dt>U+003E GREATER-THAN SIGN (&gt;)

     <dd>Emit the current DOCTYPE token. Switch to the <a
      href="#data-state">data state</a>.

     <dt>EOF

     <dd><a href="#parse">Parse error</a>. Emit the current DOCTYPE token.
      Reconsume the EOF character in the <a href="#data-state">data
      state</a>.

     <dt>Anything else

     <dd>Stay in the <a href="#bogus0">bogus DOCTYPE state</a>.
    </dl>
  </dl>

  <p>A <dfn id=permitted>permitted slash</dfn> is a U+002F SOLIDUS character
   that is immediately followed by a U+003E GREATER-THAN SIGN, if, and only
   if, the current token being processed is a start tag token whose tag name
   is one of the following: <code><a href="#base">base</a></code>, <code><a
   href="#link">link</a></code>, <code><a href="#meta0">meta</a></code>,
   <code><a href="#hr">hr</a></code>, <code><a href="#br">br</a></code>,
   <code><a href="#img">img</a></code>, <code><a
   href="#embed">embed</a></code>, <code><a href="#param">param</a></code>,
   <code><a href="#area">area</a></code>, <code><a
   href="#col">col</a></code>, <code>input</code><!-- XXX add:
  , <code>command</code>, <code>event-source</code> --></p>
  <!-- XXX
  keep this synchronised with the list of "void elements" -->

  <h5 id=tokenising><span class=secno>8.2.3.1. </span>Tokenising entities</h5>

  <p>This section defines how to <dfn id=consume>consume an entity</dfn>.
   This definition is used when parsing entities <a href="#entity"
   title="entity data state">in text</a> and <a href="#entity0" title="entity
   in attribute value state">in attributes</a>.

  <p>The behaviour depends on the identity of the next character (the one
   immediately after the U+0026 AMPERSAND character):

  <dl class=switch>
   <dt>U+0023 NUMBER SIGN (#)

   <dd>
    <p>Consume the U+0023 NUMBER SIGN.</p>

    <p>The behaviour further depends on the character after the U+0023 NUMBER
     SIGN:</p>

    <dl class=switch>
     <dt>U+0078 LATIN SMALL LETTER X

     <dt>U+0058 LATIN CAPITAL LETTER X

     <dd>
      <p>Consume the X.</p>

      <p>Follow the steps below, but using the range of characters U+0030
       DIGIT ZERO through to U+0039 DIGIT NINE, U+0061 LATIN SMALL LETTER A
       through to U+0066 LATIN SMALL LETTER F, and U+0041 LATIN CAPITAL
       LETTER A, through to U+0046 LATIN CAPITAL LETTER F (in other words,
       0-9, A-F, a-f).</p>

      <p>When it comes to interpreting the number, interpret it as a
       hexadecimal number.</p>

     <dt>Anything else

     <dd>
      <p>Follow the steps below, but using the range of characters U+0030
       DIGIT ZERO through to U+0039 DIGIT NINE (i.e. just 0-9).</p>

      <p>When it comes to interpreting the number, interpret it as a decimal
       number.</p>
    </dl>

    <p>Consume as many characters as match the range of characters given
     above.</p>

    <p>If no characters match the range, then don't consume any characters
     (and unconsume the U+0023 NUMBER SIGN character and, if appropriate, the
     X character). This is a <a href="#parse">parse error</a>; nothing is
     returned.</p>

    <p>Otherwise, if the next character is a U+003B SEMICOLON, consume that
     too. If it isn't, there is a <a href="#parse">parse error</a>.</p>

    <p>If one or more characters match the range, then take them all and
     interpret the string of characters as a number (either hexadecimal or
     decimal as appropriate).

    <p>If that number is in the range 128 to 159 (0x80 to 0x9F), then this is
     a <a href="#parse">parse error</a>. In the following table, find the row
     with that number in the first column, and return a character token for
     the Unicode character given in the second column of that row.</p>

    <table>
     <thead>
      <tr>
       <th>Number

       <th colspan=2>Unicode character

     <tbody>
      <tr>
       <td>0x80

       <td>U+20AC

       <td>EURO SIGN ('&#x20AC')

      <tr>
       <td>0x81

       <td>U+FFFD

       <td>REPLACEMENT CHARACTER

      <tr>
       <td>0x82

       <td>U+201A

       <td>SINGLE LOW-9 QUOTATION MARK ('&#x201A')

      <tr>
       <td>0x83

       <td>U+0192

       <td>LATIN SMALL LETTER F WITH HOOK ('&#x0192')

      <tr>
       <td>0x84

       <td>U+201E

       <td>DOUBLE LOW-9 QUOTATION MARK ('&#x201E')

      <tr>
       <td>0x85

       <td>U+2026

       <td>HORIZONTAL ELLIPSIS ('&#x2026')

      <tr>
       <td>0x86

       <td>U+2020

       <td>DAGGER ('&#x2020')

      <tr>
       <td>0x87

       <td>U+2021

       <td>DOUBLE DAGGER ('&#x2021')

      <tr>
       <td>0x88

       <td>U+02C6

       <td>MODIFIER LETTER CIRCUMFLEX ACCENT ('&#x02C6')

      <tr>
       <td>0x89

       <td>U+2030

       <td>PER MILLE SIGN ('&#x2030')

      <tr>
       <td>0x8A

       <td>U+0160

       <td>LATIN CAPITAL LETTER S WITH CARON ('&#x0160')

      <tr>
       <td>0x8B

       <td>U+2039

       <td>SINGLE LEFT-POINTING ANGLE QUOTATION MARK ('&#x2039')

      <tr>
       <td>0x8C

       <td>U+0152

       <td>LATIN CAPITAL LIGATURE OE ('&#x0152')

      <tr>
       <td>0x8D

       <td>U+FFFD

       <td>REPLACEMENT CHARACTER

      <tr>
       <td>0x8E

       <td>U+017D

       <td>LATIN CAPITAL LETTER Z WITH CARON ('&#x017D')

      <tr>
       <td>0x8F

       <td>U+FFFD

       <td>REPLACEMENT CHARACTER

      <tr>
       <td>0x90

       <td>U+FFFD

       <td>REPLACEMENT CHARACTER

      <tr>
       <td>0x91

       <td>U+2018

       <td>LEFT SINGLE QUOTATION MARK ('&#x2018')

      <tr>
       <td>0x92

       <td>U+2019

       <td>RIGHT SINGLE QUOTATION MARK ('&#x2019')

      <tr>
       <td>0x93

       <td>U+201C

       <td>LEFT DOUBLE QUOTATION MARK ('&#x201C')

      <tr>
       <td>0x94

       <td>U+201D

       <td>RIGHT DOUBLE QUOTATION MARK ('&#x201D')

      <tr>
       <td>0x95

       <td>U+2022

       <td>BULLET ('&#x2022')

      <tr>
       <td>0x96

       <td>U+2013

       <td>EN DASH ('&#x2013')

      <tr>
       <td>0x97

       <td>U+2014

       <td>EM DASH ('&#x2014')

      <tr>
       <td>0x98

       <td>U+02DC

       <td>SMALL TILDE ('&#x02DC')

      <tr>
       <td>0x99

       <td>U+2122

       <td>TRADE MARK SIGN ('&#x2122')

      <tr>
       <td>0x9A

       <td>U+0161

       <td>LATIN SMALL LETTER S WITH CARON ('&#x0161')

      <tr>
       <td>0x9B

       <td>U+203A

       <td>SINGLE RIGHT-POINTING ANGLE QUOTATION MARK ('&#x203A')

      <tr>
       <td>0x9C

       <td>U+0153

       <td>LATIN SMALL LIGATURE OE ('&#x0153')

      <tr>
       <td>0x9D

       <td>U+FFFD

       <td>REPLACEMENT CHARACTER

      <tr>
       <td>0x9E

       <td>U+017E

       <td>LATIN SMALL LETTER Z WITH CARON ('&#x017E')

      <tr>
       <td>0x9F

       <td>U+0178

       <td>LATIN CAPITAL LETTER Y WITH DIAERESIS ('&#x0178')
    </table>

    <p>Otherwise, if the number is not a valid Unicode character (e.g. if the
     number is higher than 1114111), or if the number is zero, then return a
     character token for the U+FFFD REPLACEMENT CHARACTER character instead.</p>

    <p>Otherwise, return a character token for the Unicode character whose
     code point is that number.

   <dt>Anything else

   <dd>
    <p>Consume the maximum number of characters possible, with the consumed
     characters case-sensitively matching one of the identifiers in the first
     column of the <a href="#entities0">entities</a> table.</p>

    <p>If no match can be made, then this is a <a href="#parse">parse
     error</a>. No characters are consumed, and nothing is returned.</p>

    <p>Otherwise, if the next character is a U+003B SEMICOLON, consume that
     too. If it isn't, there is a <a href="#parse">parse error</a>.</p>

    <p>Return a character token for the character corresponding to the entity
     name (as given by the second column of the <a
     href="#entities0">entities</a> table).</p>

    <div class=example>
     <p>If the markup contains <code title="">I'm &amp;notit without
      you</code>, the entity is parsed as "not", as in, <code title="">I'm
      &not;it without you</code>. But if the markup was <code title="">I'm
      &amp;notin without you</code>, the entity would be parsed as "notin",
      resulting in <code title="">I'm &notin; without you</code>.</p>
    </div>
  </dl>

  <p class=big-issue>This isn't quite right. For some entities, UAs require a
   semicolon, for others they don't. We probably need to do the same for
   backwards compatibility. If we do that we might be able to add more
   entities, e.g. for mathematics. Probably the way to mark whether or not an
   entity requires a semicolon is with an additional column in the <a
   href="#entities0" title=entities>entity table lower down</a>.

  <p class=big-issue>It seems browsers convert CRs to LFs even as entities.
   Should we also do that? If so, we should remove the CRs in the tree
   construction phase.</p>
  <!-- IE is not such a browser; you
  can prove that by comparing id="&#xA;X" to id="&#xD;X" in terms of
  getElementById('\nX') vs '\rX'. -->

  <h4 id=tree-construction><span class=secno>8.2.4. </span><dfn
   id=tree-construction0>Tree construction</dfn></h4>

  <p>The input to the tree construction stage is a sequence of tokens from
   the <a href="#tokenisation0">tokenisation</a> stage. The tree construction
   stage is associated with a DOM <code>Document</code> object when a parser
   is created. The "output" of this stage consists of dynamically modifying
   or extending that document's DOM tree.

  <p>Tree construction passes through several phases. Initially, UAs must act
   according to the steps described as being those of <a
   href="#the-initial0">the initial phase</a>.

  <p>This specification does not define when an interactive user agent has to
   render the <code>Document</code> available to the user, or when it has to
   begin accepting user input.

  <p>When the steps below require the UA to <dfn id=append>append a
   character</dfn> to a node, the UA must collect it and all subsequent
   consecutive characters that would be appended to that node, and insert one
   <code>Text</code> node whose data is the concatenation of all those
   characters.

  <p id=mutation-during-parsing>DOM mutation events must not fire for changes
   caused by the UA parsing the document. (Conceptually, the parser is not
   mutating the DOM, it is constructing it.) This includes the parsing of any
   content inserted using <code title=dom-document-write-HTML><a
   href="#document.write0">document.write()</a></code> and <code
   title=dom-document-writeln><a
   href="#document.writeln">document.writeln()</a></code> calls.<!--
  XXX xref -->
   <a href="#refsDOM3EVENTS">[DOM3EVENTS]</a></p>
  <!-- XXX
  what abotu innerHTML? -->

  <p class=note>Not all of the tag names mentioned below are conformant tag
   names in this specification; many are included to handle legacy content.
   They still form part of the algorithm that implementations are required to
   implement to claim conformance.

  <p class=note>The algorithm described below places no limit on the depth of
   the DOM tree generated, or on the length of tag names, attribute names,
   attribute values, text nodes, etc. While implementators are encouraged to
   avoid arbitrary limits, it is recognised that <a
   href="#hardwareLimitations">practical concerns</a> will likely force user
   agents to impose nesting depths.

  <h5 id=the-initial><span class=secno>8.2.4.1. </span><dfn
   id=the-initial0>The initial phase</dfn></h5>

  <p>Initially, the tree construction stage must handle each token emitted
   from the <a href="#tokenisation0">tokenisation</a> stage as follows:

  <dl class=switch>
   <dt>A DOCTYPE token that is marked as being in error

   <dt>A comment token

   <dt>A start tag token

   <dt>An end tag token

   <dt>A character token that is not one of one of U+0009 CHARACTER
    TABULATION, U+000A LINE FEED (LF), U+000B LINE TABULATION, U+000C FORM
    FEED (FF), U+000D CARRIAGE RETURN (CR), or U+0020 SPACE

   <dt>An end-of-file token

   <dd>
    <p>This specification does not define how to handle this case. In
     particular, user agents may ignore the entirety of this specification
     altogether for such documents, and instead invoke special parse modes
     with a greater emphasis on backwards compatibility.</p>

    <div class=note>
     <p>Browsers in particular have generally used DOCTYPE-based sniffing to
      invoke an "alternative conformance mode" known as <em>quirks mode</em>
      on certain documents. In this mode, emphasis is put on legacy
      compatibility rather than on standards compliance. This specification
      takes no position on this behaviour; documents without DOCTYPEs or with
      DOCTYPEs that do not conform to the syntax allowed by this
      specification are considered to be out of scope of this specification.</p>
    </div>

    <div class=big-issue>
     <p>As far as parsing goes, the quirks I know of are:</p>

     <ul>
      <li>Comment parsing is different.

      <li><code title="">&lt;/br></code> and <code title="">&lt;/p></code> do
       magical things.

      <li><code><a href="#p">p</a></code> can contain <code><a
       href="#table">table</a></code>

      <li>Safari and IE have special parsing rules for &lt;% ... %&gt; (even
       in standards mode, though clearly this should be quirks-only).
     </ul>

     <p>Maybe we should just adopt all those and be done with it. One parsing
      mode to rule them all. Or legitimise/codify the quirks mode parsing in
      some way.</p>

     <p>Would be interesting to do a search to see how many pages hit each of
      the above.</p>
     <!-- biased by page rank? --></div>

   <dt>A DOCTYPE token marked as being correct

   <dd>
    <p>Append a <code>DocumentType</code> node to the <code>Document</code>
     node, with the <code title="">name</code> attribute set to the name
     given in the DOCTYPE token (which will be "HTML"), and the other
     attributes specific to <code>DocumentType</code> objects set to null,
     empty lists, or the empty string as appropriate.</p>

    <p>Then, switch to <a href="#the-root1">the root element phase</a> of the
     tree construction stage.</p>
    <!-- XXX should set doctype on the Document object, too, unless
    spec is defined to already point to it if you append -->
    

   <dt>A character token that <em>is</em> one of one of U+0009 CHARACTER
    TABULATION, U+000A LINE FEED (LF), U+000B LINE TABULATION, U+000C FORM
    FEED (FF), U+000D CARRIAGE RETURN (CR), or U+0020 SPACE

   <dd>
    <p><a href="#append" title="append a character">Append that character</a>
     to the <code>Document</code> node.</p>
  </dl>

  <h5 id=the-root0><span class=secno>8.2.4.2. </span><dfn id=the-root1>The
   root element phase</dfn></h5>

  <p>After <a href="#the-initial0">the initial phase</a>, as each token is
   emitted from the <a href="#tokenisation0">tokenisation</a> stage, it must
   be processed as described in this section.

  <dl class=switch>
   <dt>A DOCTYPE token

   <dd>
    <p><a href="#parse">Parse error</a>. Ignore the token.</p>

   <dt>A comment token

   <dd>
    <p>Append a <code>Comment</code> node to the <code>Document</code> object
     with the <code title="">data</code> attribute set to the data given in
     the comment token.</p>

   <dt>A character token that is one of one of U+0009 CHARACTER TABULATION,
    U+000A LINE FEED (LF), U+000B LINE TABULATION, U+000C FORM FEED (FF),
    U+000D CARRIAGE RETURN (CR), or U+0020 SPACE

   <dd>
    <p><a href="#append" title="append a character">Append that character</a>
     to the <code>Document</code> node.</p>

   <dt>A character token that is <em>not</em> one of U+0009 CHARACTER
    TABULATION, U+000A LINE FEED (LF), U+000B LINE TABULATION, U+000C FORM
    FEED (FF), U+000D CARRIAGE RETURN (CR), or U+0020 SPACE

   <dt>A start tag token

   <dt>An end tag token

   <dt>An end-of-file token

   <dd>
    <p>Create an <code><a href="#htmlelement">HTMLElement</a></code> node
     with the tag name <code><a href="#html">html</a></code>, in the <a
     href="#html-namespace0">HTML namespace</a>. Append it to the
     <code>Document</code> object. Switch to <a href="#the-main0">the main
     phase</a> and reprocess the current token.</p>

    <p class=big-issue>Should probably make end tags be ignored, so that
     "&lt;/head>&lt;!-- -->&lt;html>" puts the comment befor the root node
     (or should we?)</p>
  </dl>

  <p>The root element can end up being removed from the <code>Document</code>
   object, e.g. by scripts; nothing in particular happens in such cases,
   content continues being appended to the nodes as described in the next
   section.

  <h5 id=the-main><span class=secno>8.2.4.3. </span><dfn id=the-main0>The
   main phase</dfn></h5>

  <p>After <a href="#the-root1">the root element phase</a>, each token
   emitted from the <a href="#tokenisation0">tokenisation</a> stage must be
   processed as described in <em>this</em> section. This is by far the most
   involved part of parsing an HTML document.

  <p>The tree construction stage in this phase has several pieces of state: a
   <a href="#stack">stack of open elements</a>, a <a href="#list-of4">list of
   active formatting elements</a>, a <a href="#head-element"><code
   title="">head</code> element pointer</a>, a <a href="#form-element"><code
   title="">form</code> element pointer</a>, and an <a
   href="#insertion0">insertion mode</a>.

  <p class=big-issue>We could just fold insertion modes and phases into one
   concept (and duplicate the two rules common to all insertion modes into
   all of them).

  <h6 id=the-stack><span class=secno>8.2.4.3.1. </span>The stack of open
   elements</h6>

  <p>Initially the <dfn id=stack>stack of open elements</dfn> contains just
   the <code><a href="#html">html</a></code> root element node created in the
   <a href="#the-root1" title="the root element phase">last phase</a> before
   switching to <em>this</em> phase (or, in the <a
   href="#innerhtml1"><code>innerHTML</code> case</a>, the <code><a
   href="#html">html</a></code> element created to represent the element
   whose <code title=dom-innerHTML-HTML><a
   href="#innerhtml0">innerHTML</a></code> attribute is being set). That's
   the topmost node of the stack. It never gets popped off the stack. (This
   stack grows downwards.)

  <p>The <dfn id=current4>current node</dfn> is the bottommost node in this
   stack.

  <p>Elements in the stack fall into the following categories:

  <dl>
   <dt><dfn id=special>Special</dfn>

   <dd>
    <p>The following HTML elements have varying levels of special parsing
     rules: <code><a href="#address">address</a></code>, <code><a
     href="#area">area</a></code>, <code><a href="#base">base</a></code>,
     <code>basefont</code>, <code>bgsound</code>, <code><a
     href="#blockquote">blockquote</a></code>, <code><a
     href="#body0">body</a></code>, <code><a href="#br">br</a></code>,
     <code>center</code>, <code><a href="#col">col</a></code>, <code><a
     href="#colgroup">colgroup</a></code>, <code><a href="#dd">dd</a></code>,
     <code>dir</code>, <code><a href="#div">div</a></code>, <code><a
     href="#dl">dl</a></code>, <code><a href="#dt">dt</a></code>, <code><a
     href="#embed">embed</a></code>, <code>fieldset</code>,
     <code>form</code>, <code>frame</code>, <code>frameset</code>, <code><a
     href="#h1">h1</a></code>, <code><a href="#h2">h2</a></code>, <code><a
     href="#h3">h3</a></code>, <code><a href="#h4">h4</a></code>, <code><a
     href="#h5">h5</a></code>, <code><a href="#h6">h6</a></code>, <code><a
     href="#head">head</a></code>, <code><a href="#hr">hr</a></code>,
     <code><a href="#iframe">iframe</a></code>,
     <code>image</code><!-- XXX ? this isn't an element that can end up
   on the stack-->,
     <code><a href="#img">img</a></code>, <code>input</code>,
     <code>isindex</code>, <code><a href="#li">li</a></code>, <code><a
     href="#link">link</a></code>, <code>listing</code>, <code><a
     href="#menu">menu</a></code>, <code><a href="#meta0">meta</a></code>,
     <code>noembed</code>, <code>noframes</code>, <code><a
     href="#noscript">noscript</a></code>, <code><a href="#ol">ol</a></code>,
     <code>optgroup</code>, <code>option</code>, <code><a
     href="#p">p</a></code>, <code><a href="#param">param</a></code>,
     <code>plaintext</code>, <code><a href="#pre">pre</a></code>, <code><a
     href="#script0">script</a></code>, <code>select</code>,
     <code>spacer</code>, <code><a href="#style">style</a></code>, <code><a
     href="#tbody">tbody</a></code>, <code>textarea</code>, <code><a
     href="#tfoot0">tfoot</a></code>, <code><a
     href="#thead0">thead</a></code>, <code><a
     href="#title1">title</a></code>, <code><a href="#tr">tr</a></code>,
     <code><a href="#ul">ul</a></code>, and <code>wbr</code>.

   <dt><dfn id=scoping>Scoping</dfn>

   <dd>
    <p>The following HTML elements introduce new <a href="#have-an"
     title="has an element in scope">scopes</a> for various parts of the
     parsing: <code>button</code>, <code><a
     href="#caption0">caption</a></code>, <code><a
     href="#html">html</a></code>, <code>marquee</code>, <code><a
     href="#object">object</a></code>, <code><a
     href="#table">table</a></code>, <code><a href="#td">td</a></code> and
     <code><a href="#th">th</a></code>.

   <dt><dfn id=formatting>Formatting</dfn>

   <dd>
    <p>The following HTML elements are those that end up in the <a
     href="#list-of4">list of active formatting elements</a>: <code><a
     href="#a">a</a></code>, <code><a href="#b">b</a></code>,
     <code>big</code>, <code><a href="#em">em</a></code>, <code><a
     href="#font">font</a></code>, <code><a href="#i">i</a></code>,
     <code>nobr</code>, <code>s</code>, <code><a
     href="#small">small</a></code>, <code>strike</code>, <code><a
     href="#strong">strong</a></code>, <code>tt</code>, and <code>u</code>.

   <dt><dfn id=phrasing>Phrasing</dfn>

   <dd>
    <p>All other elements found while parsing an HTML document.
  </dl>

  <p class=big-issue>Still need to add these new elements to the lists:
   <code><a href="#event-source">event-source</a></code>, <code><a
   href="#section">section</a></code>, <code><a href="#nav">nav</a></code>,
   <code><a href="#article">article</a></code>, <code><a
   href="#aside">aside</a></code>, <code><a href="#header">header</a></code>,
   <code><a href="#footer">footer</a></code>, <code><a
   href="#datagrid0">datagrid</a></code>, <code><a
   href="#command0">command</a></code>

  <p>The <a href="#stack">stack of open elements</a> is said to <dfn
   id=have-an title="has an element in scope">have an element in scope</dfn>
   or <dfn id=have-an0 title="has an element in table scope">have an element
   in <em>table scope</em></dfn> when the following algorithm terminates in a
   match state:

  <ol>
   <li>
    <p>Initialise <var title="">node</var> to be the <a
     href="#current4">current node</a> (the bottommost node of the stack).

   <li>
    <p>If <var title="">node</var> is the target node, terminate in a match
     state.

   <li>
    <p>Otherwise, if <var title="">node</var> is a <code><a
     href="#table">table</a></code> element, terminate in a failure state.

   <li>
    <p>Otherwise, if the algorithm is the "has an element in scope" variant
     (rather than the "has an element in table scope" variant), and <var
     title="">node</var> is one of the following, terminate in a failure
     state:</p>

    <ul class=brief>
     <li><code><a href="#caption0">caption</a></code>

     <li><code><a href="#td">td</a></code>

     <li><code><a href="#th">th</a></code>

     <li><code>button</code>

     <li><code>marquee</code>

     <li><code><a href="#object">object</a></code>
    </ul>

   <li>
    <p>Otherwise, if <var title="">node</var> is an <code><a
     href="#html">html</a></code> element, terminate in a failure state.
     (This can only happen if the <var title="">node</var> is the topmost
     node of the <a href="#stack">stack of open elements</a>, and prevents
     the next step from being invoked if there are no more elements in the
     stack.)

   <li>
    <p>Otherwise, set <var title="">node</var> to the previous entry in the
     <a href="#stack">stack of open elements</a> and return to step 2. (This
     will never fail, since the loop will always terminate in the previous
     step if the top of the stack is reached.)
  </ol>

  <p>Nothing happens if at any time any of the elements in the <a
   href="#stack">stack of open elements</a> are moved to a new location in,
   or removed from, the <code>Document</code> tree. In particular, the stack
   is not changed in this situation. This can cause, amongst other strange
   effects, content to be appended to nodes that are no longer in the DOM.

  <p class=note>In some cases (namely, when <a href="#adoptionAgency">closing
   misnested formatting elements</a>), the stack is manipulated in a
   random-access fashion.

  <h6 id=the-list><span class=secno>8.2.4.3.2. </span>The list of active
   formatting elements</h6>

  <p>Initially the <dfn id=list-of4>list of active formatting elements</dfn>
   is empty. It is used to handle mis-nested <a href="#formatting"
   title=formatting>formatting element tags</a>.

  <p>The list contains elements in the <a href="#formatting">formatting</a>
   category, and scope markers. The scope markers are inserted when entering
   buttons, <code><a href="#object">object</a></code> elements, marquees,
   table cells, and table captions, and are used to prevent formatting from
   "leaking" into tables, buttons, <code><a href="#object">object</a></code>
   elements, and marquees.

  <p>When the steps below require the UA to <dfn id=reconstruct>reconstruct
   the active formatting elements</dfn>, the UA must perform the following
   steps:

  <ol>
   <li>If there are no entries in the <a href="#list-of4">list of active
    formatting elements</a>, then there is nothing to reconstruct; stop this
    algorithm.

   <li>If the last (most recently added) entry in the <a
    href="#list-of4">list of active formatting elements</a> is a marker, or
    if it is an element that is in the <a href="#stack">stack of open
    elements</a>, then there is nothing to reconstruct; stop this algorithm.

   <li>Let <var title="">entry</var> be the last (most recently added)
    element in the <a href="#list-of4">list of active formatting
    elements</a>.

   <li>If there are no entries before <var title="">entry</var> in the <a
    href="#list-of4">list of active formatting elements</a>, then jump to
    step 8.

   <li>Let <var title="">entry</var> be the entry one earlier than <var
    title="">entry</var> in the <a href="#list-of4">list of active formatting
    elements</a>.

   <li>If <var title="">entry</var> is neither a marker nor an element that
    is also in the <a href="#stack">stack of open elements</a>, go to step 4.

   <li>Let <var title="">entry</var> be the element one later than <var
    title="">entry</var> in the <a href="#list-of4">list of active formatting
    elements</a>.

   <li>Perform a shallow clone of the element <var title="">entry</var> to
    obtain <var title="">clone</var>. <a href="#refsDOM3CORE">[DOM3CORE]</a>

   <li>Append <var title="">clone</var> to the <a href="#current4">current
    node</a> and push it onto the <a href="#stack">stack of open elements</a>
    so that it is the new <a href="#current4">current node</a>.

   <li>Replace the entry for <var title="">entry</var> in the list with an
    entry for <var title="">clone</var>.

   <li>If the entry for <var title="">clone</var> in the <a
    href="#list-of4">list of active formatting elements</a> is not the last
    entry in the list, return to step 7.
  </ol>

  <p>This has the effect of reopening all the formatting elements that were
   opened in the current body, cell, or caption (whichever is youngest) that
   haven't been explicitly closed.

  <p class=note>The way this specification is written, the <a
   href="#list-of4">list of active formatting elements</a> always consists of
   elements in chronological order with the least recently added element
   first and the most recently added element last (except for while steps 8
   to 11 of the above algorithm are being executed, of course).

  <p>When the steps below require the UA to <dfn id=clear0>clear the list of
   active formatting elements up to the last marker</dfn>, the UA must
   perform the following steps:

  <ol>
   <li>Let <var title="">entry</var> be the last (most recently added) entry
    in the <a href="#list-of4">list of active formatting elements</a>.

   <li>Remove <var title="">entry</var> from the <a href="#list-of4">list of
    active formatting elements</a>.

   <li>If <var title="">entry</var> was a marker, then stop the algorithm at
    this point. The list has been cleared up to the last marker.

   <li>Go to step 1.
  </ol>

  <h6 id=creating><span class=secno>8.2.4.3.3. </span>Creating and inserting
   HTML elements</h6>

  <p>When the steps below require the UA to <dfn id=create title="create an
   element for the token">create an element for a token</dfn>, the UA must
   create a node implementing the interface appropriate for the element type
   corresponding to the tag name of the token (as given in the section of
   this specification that defines that element, e.g. for an <code><a
   href="#a">a</a></code> element it would be the <code><a
   href="#htmlanchorelement">HTMLAnchorElement</a></code> interface), with
   the tag name being the name of that element, with the node being in the <a
   href="#html-namespace0">HTML namespace</a>, and with the attributes on the
   node being those given in the given token.

  <p>When the steps below require the UA to <dfn id=insert>insert an HTML
   element</dfn> for a token, the UA must first <a href="#create">create an
   element for the token</a>, and then append this node to the <a
   href="#current4">current node</a>, and push it onto the <a
   href="#stack">stack of open elements</a> so that it is the new <a
   href="#current4">current node</a>.

  <p>The steps below may also require that the UA insert an HTML element in a
   particular place, in which case the UA must <a href="#create">create an
   element for the token</a> and then insert or append the new node in the
   location specified. (This happens in particular during the parsing of
   tables with invalid content.)

  <p>The interface appropriate for an element that is not defined in this
   specification is <code><a href="#htmlelement">HTMLElement</a></code>.

  <h6 id=closing><span class=secno>8.2.4.3.4. </span>Closing elements that
   have implied end tags</h6>

  <p>When the steps below require the UA to <dfn id=generate>generate implied
   end tags</dfn>, then, if the <a href="#current4">current node</a> is a
   <code><a href="#dd">dd</a></code> element, a <code><a
   href="#dt">dt</a></code> element, an <code><a href="#li">li</a></code>
   element, a <code><a href="#p">p</a></code> element, a <code><a
   href="#td">td</a></code> element, a <code><a href="#th">th</a></code>
   element, or a <code><a href="#tr">tr</a></code> element, the UA must act
   as if an end tag with the respective tag name had been seen and then <a
   href="#generate">generate implied end tags</a> again.

  <p>The step that requires the UA to generate implied end tags but lists an
   element to exclude from the process, then the UA must perform the above
   steps as if that element was not in the above list.

  <h6 id=the-element><span class=secno>8.2.4.3.5. </span>The element pointers</h6>

  <p>Initially the <dfn id=head-element><code title="">head</code> element
   pointer</dfn> and the <dfn id=form-element><code title="">form</code>
   element pointer</dfn> are both null.

  <p>Once a <code><a href="#head">head</a></code> element has been parsed
   (whether implicitly or explicitly) the <a href="#head-element"><code
   title="">head</code> element pointer</a> gets set to point to this node.

  <p>The <a href="#form-element"><code title="">form</code> element
   pointer</a> points to the last <code>form</code> element that was opened
   and whose end tag has not yet been seen. It is used to make form controls
   associate with forms in the face of dramatically bad markup, for
   historical reasons.

  <h6 id=the-insertion><span class=secno>8.2.4.3.6. </span>The insertion mode</h6>

  <p>Initially the <dfn id=insertion0>insertion mode</dfn> is "<a
   href="#before2" title="insertion mode: before head">before head</a>". It
   can change to "<a href="#in-head" title="insertion mode: in head">in
   head</a>", "<a href="#after1" title="insertion mode: after head">after
   head</a>", "<a href="#in-body" title="insertion mode: in body">in
   body</a>", "<a href="#in-table" title="insertion mode: in table">in
   table</a>", "<a href="#in-caption" title="insertion mode: in caption">in
   caption</a>", "<a href="#in-column" title="insertion mode: in column
   group">in column group</a>", "<a href="#in-table0" title="insertion mode:
   in table body">in table body</a>", "<a href="#in-row" title="insertion
   mode: in row">in row</a>", "<a href="#in-cell" title="insertion mode: in
   cell">in cell</a>", "<a href="#in-select" title="insertion mode: in
   select">in select</a>", "<a href="#after2" title="insertion mode: after
   body">after body</a>", "<a href="#in-frameset" title="insertion mode: in
   frameset">in frameset</a>", and "<a href="#after3" title="insertion mode:
   after frameset">after frameset</a>" during the course of the parsing, as
   described below. It affects how certain tokens are processed.

  <p>If the tree construction stage is switched from <a href="#the-main0">the
   main phase</a> to <a href="#the-trailing0">the trailing end phase</a> and
   back again, the various pieces of state are not reset; the UA must act as
   if the state was maintained.

  <p>When the steps below require the UA to <dfn id=reset>reset the insertion
   mode appropriately</dfn>, it means the UA must follow these steps:

  <ol>
   <li>Let <var title="">last</var> be false.

   <li>Let <var title="">node</var> be the last node in the <a
    href="#stack">stack of open elements</a>.

   <li>If <var title="">node</var> is the first node in the stack of open
    elements, then set <var title="">last</var> to true. If the element whose
    <code title=dom-innerHTML-HTML><a href="#innerhtml0">innerHTML</a></code>
    attribute is being set is neither a <code><a href="#td">td</a></code>
    element nor a <code><a href="#th">th</a></code> element, then set <var
    title="">node</var> to the element whose <code
    title=dom-innerHTML-HTML><a href="#innerhtml0">innerHTML</a></code>
    attribute is being set. (<a href="#innerhtml1"><code>innerHTML</code>
    case</a>)

   <li>If <var title="">node</var> is a <code>select</code> element, then
    switch the <a href="#insertion0">insertion mode</a> to "<a
    href="#in-select" title="insertion mode: in select">in select</a>" and
    abort these steps. (<a href="#innerhtml1"><code>innerHTML</code>
    case</a>)

   <li>If <var title="">node</var> is a <code><a href="#td">td</a></code> or
    <code><a href="#th">th</a></code> element, then switch the <a
    href="#insertion0">insertion mode</a> to "<a href="#in-cell"
    title="insertion mode: in cell">in cell</a>" and abort these steps.

   <li>If <var title="">node</var> is a <code><a href="#tr">tr</a></code>
    element, then switch the <a href="#insertion0">insertion mode</a> to "<a
    href="#in-row" title="insertion mode: in row">in row</a>" and abort these
    steps.

   <li>If <var title="">node</var> is a <code><a
    href="#tbody">tbody</a></code>, <code><a href="#thead0">thead</a></code>,
    or <code><a href="#tfoot0">tfoot</a></code> element, then switch the <a
    href="#insertion0">insertion mode</a> to "<a href="#in-table0"
    title="insertion mode: in table body">in table body</a>" and abort these
    steps.

   <li>If <var title="">node</var> is a <code><a
    href="#caption0">caption</a></code> element, then switch the <a
    href="#insertion0">insertion mode</a> to "<a href="#in-caption"
    title="insertion mode: in caption">in caption</a>" and abort these steps.

   <li>If <var title="">node</var> is a <code><a
    href="#colgroup">colgroup</a></code> element, then switch the <a
    href="#insertion0">insertion mode</a> to "<a href="#in-column"
    title="insertion mode: in column group">in column group</a>" and abort
    these steps. (<a href="#innerhtml1"><code>innerHTML</code> case</a>)

   <li>If <var title="">node</var> is a <code><a
    href="#table">table</a></code> element, then switch the <a
    href="#insertion0">insertion mode</a> to "<a href="#in-table"
    title="insertion mode: in table">in table</a>" and abort these steps.

   <li>If <var title="">node</var> is a <code><a href="#head">head</a></code>
    element, then switch the <a href="#insertion0">insertion mode</a> to "<a
    href="#in-body" title="insertion mode: in body">in body</a>" ("<a
    href="#in-body" title="insertion mode: in body">in body</a>"! <em> not
    "<a href="#in-head" title="insertion mode: in head">in head</a>"</em>!)
    and abort these steps. (<a href="#innerhtml1"><code>innerHTML</code>
    case</a>)

   <li>If <var title="">node</var> is a <code><a
    href="#body0">body</a></code> element, then switch the <a
    href="#insertion0">insertion mode</a> to "<a href="#in-body"
    title="insertion mode: in body">in body</a>" and abort these steps.

   <li>If <var title="">node</var> is a <code>frameset</code> element, then
    switch the <a href="#insertion0">insertion mode</a> to "<a
    href="#in-frameset" title="insertion mode: in frameset">in frameset</a>"
    and abort these steps. (<a href="#innerhtml1"><code>innerHTML</code>
    case</a>)

   <li>If <var title="">node</var> is an <code><a
    href="#html">html</a></code> element, then: if the <a
    href="#head-element"><code title="">head</code> element pointer</a> is
    null, switch the <a href="#insertion0">insertion mode</a> to "<a
    href="#before2" title="insertion mode: before head">before head</a>",
    otherwise, switch the <a href="#insertion0">insertion mode</a> to "<a
    href="#after1" title="insertion mode: after head">after head</a>". In
    either case, abort these steps. (<a
    href="#innerhtml1"><code>innerHTML</code> case</a>)</li>
   <!-- XXX can the head element pointer ever be
   non-null when we're going through these steps? -->

   <li>If <var title="">last</var> is true, then set the <a
    href="#insertion0">insertion mode</a> to "<a href="#in-body"
    title="insertion mode: in body">in body</a>" and abort these steps. (<a
    href="#innerhtml1"><code>innerHTML</code> case</a>)

   <li>Let <var title="">node</var> now be the node before <var
    title="">node</var> in the <a href="#stack">stack of open elements</a>.

   <li>Return to step 3.
  </ol>
  <!--When you don't have to handle innerHTML, you can use this
simplified explanation instead:

  <ol>

   <li><p>If the <span>stack of open elements</span> <span title="has
   an element in table scope">has a <code>td</code> or <code>th</code>
   element in table scope</span>, then switch the <span>insertion
   mode</span> to "<span title="insertion mode: in cell">in
   cell</span>".</p></li>

   <li><p>Otherwise, if the <span>stack of open elements</span> <span
   title="has an element in table scope">has a <code>tr</code> element
   in table scope</span>, then switch the <span>insertion mode</span>
   to "<span title="insertion mode: in row">in row</span>".</p></li>

   <li><p>Otherwise, if the <span>stack of open elements</span> <span
   title="has an element in table scope">has a <code>tbody</code>,
   <code>tfoot</code>, or <code>thead</code> element in table
   scope</span>, then switch the <span>insertion mode</span> to "<span
   title="insertion mode: in table body">in table
   body</span>".</p></li>

   <li><p>Otherwise, if the <span>stack of open elements</span> <span
   title="has an element in table scope">has a <code>caption</code>
   element in table scope</span>, then switch the <span>insertion
   mode</span> to "<span title="insertion mode: in caption">in
   caption</span>".</p></li>

   ( you can't reach this point with a colgroup element on the
   stack )

   <li><p>Otherwise, if the <span>stack of open elements</span> <span
   title="has an element in table scope">has a <code>table</code>
   element in table scope</span>, then switch the <span>insertion
   mode</span> to "<span title="insertion mode: in table">in
   table</span>".</p></li>

   <li><p>Otherwise, switch the <span>insertion mode</span> to "<span
   title="insertion mode: in body">in body</span>".</p></li>

  </ol>
-->

  <h6 id=how-to0><span class=secno>8.2.4.3.7. </span>How to handle tokens in
   the main phase</h6>

  <p>Tokens in the main phase must be handled as follows:

  <dl class=switch>
   <dt>A DOCTYPE token

   <dd>
    <p><a href="#parse">Parse error</a>. Ignore the token.</p>

   <dt>A start tag token with the tag name "html"

   <dd>
    <p>If this start tag token was not the first start tag token, then it is
     a <a href="#parse">parse error</a>.</p>

    <p>For each attribute on the token, check to see if the attribute is
     already present on the top element of the <a href="#stack">stack of open
     elements</a>. If it is not, add the attribute and its corresponding
     value to that element.</p>

   <dt>An end-of-file token

   <dd>
    <p><a href="#generate">Generate implied end tags.</a></p>

    <p>If there are more than two nodes on the <a href="#stack">stack of open
     elements</a>, or if there are two nodes but the second node is not a
     <code><a href="#body0">body</a></code> node, this is a <a
     href="#parse">parse error</a>.</p>

    <p>Otherwise, if the parser was originally created in order to handle the
     setting of an element's <code title=dom-innerHTML-HTML><a
     href="#innerhtml0">innerHTML</a></code> attribute, and there's more than
     one element in the <a href="#stack">stack of open elements</a>, and the
     second node on the <a href="#stack">stack of open elements</a> is not a
     <code><a href="#body0">body</a></code> node, then this is a <a
     href="#parse">parse error</a>. (<a
     href="#innerhtml1"><code>innerHTML</code> case</a>)</p>

    <p><a href="#stops">Stop parsing.</a></p>

    <p class=big-issue>This fails because it doesn't imply HEAD and BODY
     tags. We should probably expand out the insertion modes and merge them
     with phases and then put the three things here into each insertion mode
     instead of trying to factor them out so carefully.</p>

   <dt>Anything else

   <dd>
    <p>Depends on the <a href="#insertion0">insertion mode</a>:</p>

    <dl class=switch>
     <dt>If the <a href="#insertion0">insertion mode</a> is "<dfn id=before2
      title="insertion mode: before head">before head</dfn>"

     <dd>
      <p>Handle the token as follows:</p>

      <dl class=switch>
       <dt>A character token that is one of one of U+0009 CHARACTER
        TABULATION, U+000A LINE FEED (LF), U+000B LINE TABULATION, U+000C
        FORM FEED (FF), U+000D CARRIAGE RETURN (CR), or U+0020 SPACE

       <dd>
        <p><a href="#append" title="append a character">Append the
         character</a> to the <a href="#current4">current node</a>.</p>

       <dt>A comment token

       <dd>
        <p>Append a <code>Comment</code> node to the <a
         href="#current4">current node</a> with the <code
         title="">data</code> attribute set to the data given in the comment
         token.</p>

       <dt>A start tag token with the tag name "head"

       <dd>
        <p><a href="#create">Create an element for the token</a>.</p>

        <p>Set the <a href="#head-element"><code title="">head</code> element
         pointer</a> to this new element node.</p>

        <p>Append the new element to the <a href="#current4">current node</a>
         and push it onto the <a href="#stack">stack of open elements</a>.</p>

        <p>Change the <a href="#insertion0">insertion mode</a> to "<a
         href="#in-head" title="insertion mode: in head">in head</a>".</p>

       <dt>A start tag token whose tag name is one of: "base", "link",
        "meta", "script", "style", "title"

       <dd>
        <p>Act as if a start tag token with the tag name "head" and no
         attributes had been seen, then reprocess the current token.</p>

        <p class=note>This will result in a <code><a
         href="#head">head</a></code> element being generated, and with the
         current token being reprocessed in the "<a href="#in-head"
         title="insertion mode: in head">in head</a>" <a
         href="#insertion0">insertion mode</a>.</p>

       <dt>An end tag with the tag name "html"

       <dd>
        <p>Act as if a start tag token with the tag name "head" and no
         attributes had been seen, then reprocess the current token.</p>

       <dt>Any other end tag

       <dd>
        <p><a href="#parse">Parse error</a>. Ignore the token.</p>

       <dt>A character token that is <em>not</em> one of U+0009 CHARACTER
        TABULATION, U+000A LINE FEED (LF), U+000B LINE TABULATION, U+000C
        FORM FEED (FF), U+000D CARRIAGE RETURN (CR), or U+0020 SPACE

       <dt>Any other start tag token

       <dd>
        <p>Act as if a start tag token with the tag name "head" and no
         attributes had been seen, then reprocess the current token.</p>

        <p class=note>This will result in an empty <code><a
         href="#head">head</a></code> element being generated, with the
         current token being reprocessed in the "<a href="#after1"
         title="insertion mode: after head">after head</a>" <a
         href="#insertion0">insertion mode</a>.</p>
      </dl>

     <dt id=parsing-main-inhead>If the <a href="#insertion0">insertion
      mode</a> is "<dfn id=in-head title="insertion mode: in head">in
      head</dfn>"

     <dd>
      <p>Handle the token as follows.</p>

      <p class=note>The rules for handling "title", "style", and "script"
       start tags are similar, but not identical.</p>

      <p class=note>It is possible for the <a href="#tree-construction0">tree
       construction</a> stage's <a href="#the-main0" title="the main
       phase">main phase</a> to be in the "<a href="#in-head"
       title="insertion mode: in head">in head</a>" <a
       href="#insertion0">insertion mode</a> without the <a
       href="#current4">current node</a> being a <code><a
       href="#head">head</a></code> element, e.g. if a <code><a
       href="#head">head</a></code> end tag is immediately followed by a
       <code><a href="#meta0">meta</a></code> start tag.</p>

      <dl class=switch>
       <dt>A character token that is one of one of U+0009 CHARACTER
        TABULATION, U+000A LINE FEED (LF), U+000B LINE TABULATION, U+000C
        FORM FEED (FF), U+000D CARRIAGE RETURN (CR), or U+0020 SPACE

       <dd>
        <p><a href="#append" title="append a character">Append the
         character</a> to the <a href="#current4">current node</a>.</p>

       <dt>A comment token

       <dd>
        <p>Append a <code>Comment</code> node to the <a
         href="#current4">current node</a> with the <code
         title="">data</code> attribute set to the data given in the comment
         token.</p>

       <dt>A start tag with the tag name "title"

       <dd>
        <p><a href="#create">Create an element for the token</a>.</p>

        <p>Append the new element to the node pointed to by the <a
         href="#head-element"><code title="">head</code> element pointer</a>,
         or, if that is null (<a href="#innerhtml1"><code>innerHTML</code>
         case</a>), to the <a href="#current4">current node</a>.</p>

        <p>Switch the tokeniser's <a href="#content2">content model flag</a>
         to the RCDATA state.</p>

        <p>Then, collect all the character tokens that the tokeniser returns
         until it returns a token that is not a character token.</p>

        <p>If this process resulted in a collection of character tokens,
         append a single <code>Text</code> node to the <code><a
         href="#title1">title</a></code> element node whose contents is the
         concatenation of all those tokens' characters.</p>

        <p>The tokeniser's <a href="#content2">content model flag</a> will
         have switched back to the PCDATA state.</p>

        <p>If the next token is an end tag token with the tag name "title",
         ignore it. Otherwise, this is a <a href="#parse">parse error</a>.</p>

       <dt>A start tag with the tag name "style"

       <dd>
        <p><a href="#create">Create an element for the token</a>.</p>

        <p>Append the new element to the <a href="#current4">current
         node</a>, unless the <a href="#insertion0">insertion mode</a> is "<a
         href="#in-head" title="insertion mode: in head">in head</a>" and the
         <a href="#head-element"><code title="">head</code> element
         pointer</a> is not null, in which case append it to the node pointed
         to by the <a href="#head-element"><code title="">head</code> element
         pointer</a>. <!--
        <head></head><style><body> should put the style block in the
        head, and does so by switching back to in head, but the head
        isn't the current node at that point (comments should go
        between the head and the body) -->.</p>

        <p>Switch the tokeniser's <a href="#content2">content model flag</a>
         to the CDATA state.</p>

        <p>Then, collect all the character tokens that the tokeniser returns
         until it returns a token that is not a character token, or until it
         stops tokenising.</p>

        <p>If this process resulted in a collection of character tokens,
         append a single <code>Text</code> node to the <code><a
         href="#style">style</a></code> element node whose contents is the
         concatenation of all those tokens' characters.</p>

        <p>The tokeniser's <a href="#content2">content model flag</a> will
         have switched back to the PCDATA state.</p>

        <p>If the next token is an end tag token with the tag name "style",
         ignore it. Otherwise, this is a <a href="#parse">parse error</a>.</p>

       <dt id=scriptTag>A start tag with the tag name "script"

       <dd>
        <p><a href="#create">Create an element for the token</a>.</p>

        <p>Mark the element as being <a
         href="#parser-inserted">"parser-inserted"</a>. This ensures that, if
         the script is external, any <code title=dom-document-write-HTML><a
         href="#document.write0">document.write()</a></code> calls in the
         script will execute in-line, instead of blowing the document away,
         as would happen in most other cases.</p>

        <p>Switch the tokeniser's <a href="#content2">content model flag</a>
         to the CDATA state.</p>

        <p>Then, collect all the character tokens that the tokeniser returns
         until it returns a token that is not a character token, or until it
         stops tokenising.</p>

        <p>If this process resulted in a collection of character tokens,
         append a single <code>Text</code> node to the <code><a
         href="#script0">script</a></code> element node whose contents is the
         concatenation of all those tokens' characters.</p>

        <p>The tokeniser's <a href="#content2">content model flag</a> will
         have switched back to the PCDATA state.</p>

        <p>If the next token is not an end tag token with the tag name
         "script", then this is a <a href="#parse">parse error</a>; mark the
         <code><a href="#script0">script</a></code> element as <a
         href="#already">"already executed"</a>. Otherwise, the token is the
         <code><a href="#script0">script</a></code> element's end tag, so
         ignore it.</p>

        <p>If the parser was originally created in order to handle the
         setting of a node's <code title=dom-innerHTML-HTML><a
         href="#innerhtml0">innerHTML</a></code> attribute, then mark the
         <code><a href="#script0">script</a></code> element as <a
         href="#already">"already executed"</a>, and skip the rest of the
         processing described for this token (including the part below where
         "<a href="#the-script" title="the script that will execute as soon
         as the parser resumes">scripts that will execute as soon as the
         parser resumes</a>" are executed). (<a
         href="#innerhtml1"><code>innerHTML</code> case</a>)</p>

        <p class=note>Marking the <code><a href="#script0">script</a></code>
         element as "already executed" prevents it from executing when it is
         inserted into the document a few paragraphs below. Scripts missing
         their end tags and scripts that were inserted using <code
         title=dom-innerHTML-HTML><a href="#innerhtml0">innerHTML</a></code>
         aren't executed.</p>

        <p>Let the <var title="">old insertion point</var> have the same
         value as the current <a href="#insertion">insertion point</a>. Let
         the <a href="#insertion">insertion point</a> be just before the <a
         href="#next-input">next input character</a>.</p>

        <p>Append the new element to the <a href="#current4">current
         node</a>, unless the <a href="#insertion0">insertion mode</a> is "<a
         href="#in-head" title="insertion mode: in head">in head</a>" and the
         <a href="#head-element"><code title="">head</code> element
         pointer</a> is not null, in which case append it to the node pointed
         to by the <a href="#head-element"><code title="">head</code> element
         pointer</a>. <!--
        <head></head><script><body> should put the script in the head,
        and does so by switching back to in head, but the head isn't
        the current node at that point (comments should go between the
        head and the body) -->
         <a href="#running0" title="running a script">Special processing
         occurs when a <code>script</code> element is inserted into a
         document</a> that might cause some script to execute, which might
         cause <a href="#document.write0" title=dom-document-write-HTML>new
         characters to be inserted into the tokeniser</a>.</p>

        <p>Let the <a href="#insertion">insertion point</a> have the value of
         the <var title="">old insertion point</var>. (In other words,
         restore the <a href="#insertion">insertion point</a> to the value it
         had before the previous paragraph. This value might be the
         "undefined" value.)</p>

        <p id=scriptTagParserResumes>At this stage, if there is <a
         href="#the-script" title="the script that will execute as soon as
         the parser resumes">a script that will execute as soon as the parser
         resumes</a>, then:</p>

        <dl class=switch>
         <dt>If the tree construction stage is <a href="#nestedParsing">being
          called reentrantly</a>, say from a call to <code
          title=dom-document-write-HTML><a
          href="#document.write0">document.write()</a></code>:

         <dd>
          <p>Abort the processing of any nested invokations of the tokeniser,
           yielding control back to the caller. (Tokenisation will resume
           when the caller returns to the "outer" tree construction stage.)

         <dt>Otherwise:

         <dd>
          <p>Follow these steps:</p>

          <ol>
           <li>
            <p>Let <var title="">the script</var> be <a
             href="#the-script">the script that will execute as soon as the
             parser resumes</a>. There is no longer <a href="#the-script"
             title="the script that will execute as soon as the parser
             resumes">a script that will execute as soon as the parser
             resumes</a>.

           <li>
            <p><a href="#pause">Pause</a> until the script has
             <span>completed loading</span><!-- XXX xref -->.

           <li>
            <p>Let the <a href="#insertion">insertion point</a> be just
             before the <a href="#next-input">next input character</a>.

           <li>
            <p><a href="#executing0" title="executing a script block">Execute
             the script</a>.

           <li>
            <p>Let the <a href="#insertion">insertion point</a> be undefined
             again.

           <li>
            <p>If there is once again <a href="#the-script" title="the script
             that will execute as soon as the parser resumes">a script that
             will execute as soon as the parser resumes</a>, then repeat
             these steps from step 1.
          </ol>
        </dl>

       <dt>A start tag with the tag name "base", "link", or "meta"

       <dd>
        <p><a href="#create">Create an element for the token</a>.</p>

        <p>Append the new element to the node pointed to by the <a
         href="#head-element"><code title="">head</code> element pointer</a>,
         or, if that is null (<a href="#innerhtml1"><code>innerHTML</code>
         case</a>), to the <a href="#current4">current node</a>.</p>

       <dt>An end tag with the tag name "head"

       <dd>
        <p>If the <a href="#current4">current node</a> is a <code><a
         href="#head">head</a></code> element, pop the <a
         href="#current4">current node</a> off the <a href="#stack">stack of
         open elements</a>. Otherwise, this is a <a href="#parse">parse
         error</a>.</p>
        <!-- might happen if you see two </head>s
        and something in between the two sends you from "after head"
        back to "in head" -->
        
        <p>Change the <a href="#insertion0">insertion mode</a> to "<a
         href="#after1" title="insertion mode: after head">after head</a>".</p>

       <dt>An end tag with the tag name "html"

       <dd>
        <p>Act as described in the "anything else" entry below.</p>

       <dt>A start tag with the tag name "head"

       <dt>Any other end tag

       <dd>
        <p><a href="#parse">Parse error</a>. Ignore the token.</p>

       <dt>Anything else

       <dd>
        <p>If the <a href="#current4">current node</a> is a <code><a
         href="#head">head</a></code> element, act as if an end tag token
         with the tag name "head" had been seen.</p>

        <p>Otherwise, change the <a href="#insertion0">insertion mode</a> to
         "<a href="#after1" title="insertion mode: after head">after
         head</a>".</p>

        <p>Then, reprocess the current token.</p>

        <p class=big-issue>In certain UAs, <a
         href="https://bugzilla.mozilla.org/attachment.cgi?id=180157&amp;action=view">some
         elements</a> don't trigger the "in body" mode straight away, but
         instead get put into the head. Do we want to copy that?</p>
      </dl>

     <dt>If the <a href="#insertion0">insertion mode</a> is "<dfn id=after1
      title="insertion mode: after head">after head</dfn>"

     <dd>
      <p>Handle the token as follows:</p>

      <dl class=switch>
       <dt>A character token that is one of one of U+0009 CHARACTER
        TABULATION, U+000A LINE FEED (LF), U+000B LINE TABULATION, U+000C
        FORM FEED (FF), U+000D CARRIAGE RETURN (CR), or U+0020 SPACE

       <dd>
        <p><a href="#append" title="append a character">Append the
         character</a> to the <a href="#current4">current node</a>.</p>

       <dt>A comment token

       <dd>
        <p>Append a <code>Comment</code> node to the <a
         href="#current4">current node</a> with the <code
         title="">data</code> attribute set to the data given in the comment
         token.</p>

       <dt>A start tag token with the tag name "body"

       <dd>
        <p><a href="#insert" title="insert an HTML element">Insert a
         <code>body</code> element</a> for the token.</p>

        <p>Change the <a href="#insertion0">insertion mode</a> to "<a
         href="#in-body" title="insertion mode: in body">in body</a>".</p>

       <dt>A start tag token with the tag name "frameset"

       <dd>
        <p><a href="#insert" title="insert an HTML element">Insert a
         <code>frameset</code> element</a> for the token.</p>

        <p>Change the <a href="#insertion0">insertion mode</a> to "<a
         href="#in-frameset" title="insertion mode: in frameset">in
         frameset</a>".</p>

       <dt>A start tag token whose tag name is one of: "base", "link",
        "meta", "script", "style", "title"

       <dd>
        <p><a href="#parse">Parse error</a>. Switch the <a
         href="#insertion0">insertion mode</a> back to "<a href="#in-head"
         title="insertion mode: in head">in head</a>" and reprocess the
         token.</p>

       <dt>Anything else

       <dd>
        <p>Act as if a start tag token with the tag name "body" and no
         attributes had been seen, and then reprocess the current token.</p>
      </dl>

     <dt id=parsing-main-inbody>If the <a href="#insertion0">insertion
      mode</a> is "<dfn id=in-body title="insertion mode: in body">in
      body</dfn>"

     <dd>
      <p>Handle the token as follows:</p>

      <dl class=switch>
       <dt>A character token

       <dd>
        <p><a href="#reconstruct">Reconstruct the active formatting
         elements</a>, if any.</p>

        <p><a href="#append" title="append a character">Append the token's
         character</a> to the <a href="#current4">current node</a>.</p>

       <dt>A comment token

       <dd>
        <p>Append a <code>Comment</code> node to the <a
         href="#current4">current node</a> with the <code
         title="">data</code> attribute set to the data given in the comment
         token.</p>

       <dt>A start tag token whose tag name is one of: "script", "style"

       <dd>
        <p>Process the token as if the <a href="#insertion0">insertion
         mode</a> had been "<a href="#in-head" title="insertion mode: in
         head">in head</a>".</p>

       <dt>A start tag token whose tag name is one of: "base", "link",
        "meta", "title"

       <dd>
        <p><a href="#parse">Parse error</a>. Process the token as if the <a
         href="#insertion0">insertion mode</a> had been "<a href="#in-head"
         title="insertion mode: in head">in head</a>".</p>

       <dt>A start tag token with the tag name "body"

       <dd>
        <p><a href="#parse">Parse error</a>.</p>

        <p>If the second element on the <a href="#stack">stack of open
         elements</a> is not a <code><a href="#body0">body</a></code>
         element, or, if the <a href="#stack">stack of open elements</a> has
         only one node on it, then ignore the token. (<a
         href="#innerhtml1"><code>innerHTML</code> case</a>)</p>

        <p>Otherwise, for each attribute on the token, check to see if the
         attribute is already present on the <code><a
         href="#body0">body</a></code> element (the second element) on the <a
         href="#stack">stack of open elements</a>. If it is not, add the
         attribute and its corresponding value to that element.</p>

       <dt>An end tag with the tag name "body"

       <dd>
        <p>If the second element in the <a href="#stack">stack of open
         elements</a> is not a <code><a href="#body0">body</a></code>
         element, this is a <a href="#parse">parse error</a>. Ignore the
         token. (<a href="#innerhtml1"><code>innerHTML</code> case</a>)</p>

        <p>Otherwise:</p>

        <p class=big-issue>this needs to handle closing of implied elements,
         but without closing them</p>

        <p>If the <a href="#current4">current node</a> is not the <code><a
         href="#body0">body</a></code> element, then this is a <a
         href="#parse">parse error</a>.</p>

        <p>Change the <a href="#insertion0">insertion mode</a> to "<a
         href="#after2" title="insertion mode: after body">after body</a>".</p>

       <dt>An end tag with the tag name "html"

       <dd>
        <p>Act as if an end tag with tag name "body" had been seen, then, if
         that token wasn't ignored, reprocess the current token.</p>

        <p class=note>The fake end tag token here can only be ignored in the
         <a href="#innerhtml1"><code>innerHTML</code> case</a>.</p>

       <dt>A start tag whose tag name is one of: "address", "blockquote",
        "center", "dir", "div", "dl", "fieldset", "listing", "menu", "ol",
        "p", "ul"

       <dd>
        <p>If the <a href="#stack">stack of open elements</a> <a
         href="#have-an" title="has an element in scope">has a <code>p</code>
         element in scope</a>, then act as if an end tag with the tag name
         <code><a href="#p">p</a></code> had been seen.</p>

        <p><a href="#insert" title="insert an html element">Insert an HTML
         element</a> for the token.</p>

       <dt>A start tag whose tag name is "pre"

       <dd>
        <p>If the <a href="#stack">stack of open elements</a> <a
         href="#have-an" title="has an element in scope">has a <code>p</code>
         element in scope</a>, then act as if an end tag with the tag name
         <code><a href="#p">p</a></code> had been seen.</p>

        <p><a href="#insert" title="insert an html element">Insert an HTML
         element</a> for the token.</p>

        <p>If the next token is a U+000A LINE FEED (LF) character token, then
         ignore that token and move on to the next one. (Newlines at the
         start of <code><a href="#pre">pre</a></code> blocks are ignored as
         an authoring convenience.)</p>

       <dt>A start tag whose tag name is "form"

       <dd>
        <p>If the <a href="#form-element"><code title=form>form</code>
         element pointer</a> is not null, ignore the token with a <a
         href="#parse">parse error</a>.</p>

        <p>Otherwise:</p>

        <p>If the <a href="#stack">stack of open elements</a> <a
         href="#have-an" title="has an element in scope">has a <code>p</code>
         element in scope</a>, then act as if an end tag with the tag name
         <code><a href="#p">p</a></code> had been seen.</p>

        <p><a href="#insert" title="insert an html Element">Insert an HTML
         element</a> for the token, and set the <code title=form>form</code>
         element pointer to point to the element created.</p>

       <dt>A start tag whose tag name is "li"

       <dd>
        <p>If the <a href="#stack">stack of open elements</a> <a
         href="#have-an" title="has an element in scope">has a <code>p</code>
         element in scope</a>, then act as if an end tag with the tag name
         <code><a href="#p">p</a></code> had been seen.</p>

        <p>Run the following algorithm:</p>

        <ol>
         <li>
          <p>Initialise <var title="">node</var> to be the <a
           href="#current4">current node</a> (the bottommost node of the
           stack).

         <li>
          <p>If <var title="">node</var> is an <code><a
           href="#li">li</a></code> element, then pop all the nodes from the
           <a href="#current4">current node</a> up to <var
           title="">node</var>, including <var title="">node</var>, then stop
           this algorithm. If more than one node is popped, then this is a <a
           href="#parse">parse error</a>.

         <li>
          <p>If <var title="">node</var> is not in the <a
           href="#formatting">formatting</a> category, and is not in the <a
           href="#phrasing">phrasing</a> category, and is not an <code><a
           href="#address">address</a></code> or <code><a
           href="#div">div</a></code> element, then stop this algorithm.
         </li>
         <!-- an element <foo> is in this
         list if the following markup:

             <!DOCTYPE html><body><ol><li><foo><li>

         ...results in the second <li> not being (in any way) a
         descendant of the first <li>, or if <foo> is a formatting
         element that gets reopened later. -->

         <li>
          <p>Otherwise, set <var title="">node</var> to the previous entry in
           the <a href="#stack">stack of open elements</a> and return to step
           2.
        </ol>

        <p>Finally, <a href="#insert" title="insert an html element">insert
         an <code>li</code> element</a>.</p>

       <dt>A start tag whose tag name is "dd" or "dt"

       <dd>
        <p>If the <a href="#stack">stack of open elements</a> <a
         href="#have-an" title="has an element in scope">has a <code>p</code>
         element in scope</a>, then act as if an end tag with the tag name
         <code><a href="#p">p</a></code> had been seen.</p>

        <p>Run the following algorithm:</p>

        <ol>
         <li>
          <p>Initialise <var title="">node</var> to be the <a
           href="#current4">current node</a> (the bottommost node of the
           stack).

         <li>
          <p>If <var title="">node</var> is a <code><a
           href="#dd">dd</a></code> or <code><a href="#dt">dt</a></code>
           element, then pop all the nodes from the <a
           href="#current4">current node</a> up to <var title="">node</var>,
           including <var title="">node</var>, then stop this algorithm. If
           more than one node is popped, then this is a <a
           href="#parse">parse error</a>.

         <li>
          <p>If <var title="">node</var> is not in the <a
           href="#formatting">formatting</a> category, and is not in the <a
           href="#phrasing">phrasing</a> category, and is not an <code><a
           href="#address">address</a></code> or <code><a
           href="#div">div</a></code> element, then stop this algorithm.
         </li>
         <!-- an element <foo> is in this
         list if the following markup:

             <!DOCTYPE html><body><ol><dt><foo><dt>

         ...results in the second <li> not being (in any way) a
         descendant of the first <li>, or if <foo> is a formatting
         element that gets reopened later. -->

         <li>
          <p>Otherwise, set <var title="">node</var> to the previous entry in
           the <a href="#stack">stack of open elements</a> and return to step
           2.
        </ol>

        <p>Finally, <a href="#insert" title="insert an html element">insert
         an HTML element</a> with the same tag name as the token's.</p>

       <dt>A start tag token whose tag name is "plaintext"

       <dd>
        <p>If the <a href="#stack">stack of open elements</a> <a
         href="#have-an" title="has an element in scope">has a <code>p</code>
         element in scope</a>, then act as if an end tag with the tag name
         <code><a href="#p">p</a></code> had been seen.</p>

        <p><a href="#insert" title="insert an html element">Insert an HTML
         element</a> for the token.</p>

        <p>Switch the <a href="#content2">content model flag</a> to the
         PLAINTEXT state.</p>

        <p class=note>Once a start tag with the tag name "plaintext" has been
         seen, that will be the last token ever seen other than character
         tokens (and the end-of-file token), because there is no way to
         switch the <a href="#content2">content model flag</a> out of the
         PLAINTEXT state.</p>

       <dt>An end tag whose tag name is one of: "address", "blockquote",
        "center", "dir", "div", "dl", "fieldset", "listing", "menu", "ol",
        "pre", "ul"

       <dd>
        <p>If the <a href="#stack">stack of open elements</a> <a
         href="#have-an">has an element in scope</a> with the same tag name
         as that of the token, then <a href="#generate">generate implied end
         tags</a>.</p>

        <p>Now, if the <a href="#current4">current node</a> is not an element
         with the same tag name as that of the token, then this is a <a
         href="#parse">parse error</a>.</p>

        <p>If the <a href="#stack">stack of open elements</a> <a
         href="#have-an">has an element in scope</a> with the same tag name
         as that of the token, then pop elements from this stack until an
         element with that tag name has been popped from the stack.</p>
        <!-- XXX quirk (except for in certain cases?):
        <p>Otherwise, act as if a start tag with the tag name given in
        the token had been seen, then reprocess the current token.</p>
        -->
        

       <dt>An end tag whose tag name is "form"

       <dd>
        <p>If the <a href="#stack">stack of open elements</a> <a
         href="#have-an">has an element in scope</a> with the same tag name
         as that of the token, then <a href="#generate">generate implied end
         tags</a>.</p>

        <p>Now, if the <a href="#current4">current node</a> is not an element
         with the same tag name as that of the token, then this is a <a
         href="#parse">parse error</a>.</p>

        <p>Otherwise, if the <a href="#current4">current node</a> is an
         element with the same tag name as that of the token pop that element
         from the stack.</p>

        <p>In any case, set the <a href="#form-element"><code
         title="">form</code> element pointer</a> to null.</p>

       <dt>An end tag whose tag name is "p"

       <dd>
        <p>If the <a href="#stack">stack of open elements</a> <a
         href="#have-an" title="has an element in scope">has a <code>p</code>
         element in scope</a>, then <a href="#generate">generate implied end
         tags</a>, except for <code><a href="#p">p</a></code> elements.</p>

        <p>If the <a href="#current4">current node</a> is not a <code><a
         href="#p">p</a></code> element, then this is a <a
         href="#parse">parse error</a>.</p>

        <p>If the <a href="#stack">stack of open elements</a> <a
         href="#have-an" title="has an element in scope">has a <code>p</code>
         element in scope</a>, then pop elements from this stack until the
         stack no longer <a href="#have-an" title="has an element in
         scope">has a <code>p</code> element in scope</a>.</p>
        <!-- XXX quirk:
        <p>Otherwise, act as if a start tag with the tag name
        <code>p</code> had been seen, then reprocess the current
        token.</p>
        -->
        

       <dt>An end tag whose tag name is "dd", "dt", or "li"

       <dd>
        <p>If the <a href="#stack">stack of open elements</a> <a
         href="#have-an">has an element in scope</a> whose tag name matches
         the tag name of the token, then <a href="#generate">generate implied
         end tags</a>, except for elements with the same tag name as the
         token.</p>

        <p>If the <a href="#current4">current node</a> is not an element with
         the same tag name as the token, then this is a <a
         href="#parse">parse error</a>.</p>

        <p>If the <a href="#stack">stack of open elements</a> <a
         href="#have-an">has an element in scope</a> whose tag name matches
         the tag name of the token, then pop elements from this stack until
         an element with that tag name has been popped from the stack.</p>

       <dt>A start tag whose tag name is one of: "h1", "h2", "h3", "h4",
        "h5", "h6"

       <dd>
        <p>If the <a href="#stack">stack of open elements</a> <a
         href="#have-an" title="has an element in scope">has a <code>p</code>
         element in scope</a>, then act as if an end tag with the tag name
         <code><a href="#p">p</a></code> had been seen.</p>

        <p>If the <a href="#stack">stack of open elements</a> <a
         href="#have-an" title="has an element in scope">has in scope</a> an
         element whose tag name is one of "h1", "h2", "h3", "h4", "h5", or
         "h6", then this is a <a href="#parse">parse error</a>; pop elements
         from the stack until an element with one of those tag names has been
         popped from the stack.</p>

        <p><a href="#insert" title="insert an html element">Insert an HTML
         element</a> for the token.</p>

       <dt>An end tag whose tag name is one of: "h1", "h2", "h3", "h4", "h5",
        "h6"

       <dd>
        <p>If the <a href="#stack">stack of open elements</a> <a
         href="#have-an" title="has an element in scope">has in scope</a> an
         element whose tag name is one of "h1", "h2", "h3", "h4", "h5", or
         "h6", then <a href="#generate">generate implied end tags</a>.</p>

        <p>Now, if the <a href="#current4">current node</a> is not an element
         with the same tag name as that of the token, then this is a <a
         href="#parse">parse error</a>.</p>

        <p>If the <a href="#stack">stack of open elements</a> <a
         href="#have-an" title="has an element in scope">has in scope</a> an
         element whose tag name is one of "h1", "h2", "h3", "h4", "h5", or
         "h6", then pop elements from the stack until an element with one of
         those tag names has been popped from the stack.</p>
        <!-- XXX quirk:
        <p>Otherwise, act as if a start tag with the tag name given in
        the token had been seen, then reprocess the current token.</p>
        -->
        </dd>
       <!-- ADOPTION AGENCY ELEMENTS
            Mozilla-only: bdo blink del ins sub sup q
            Safari-only: code dfn kbd nobr samp var wbr
            Both: a b big em font i s small strike strong tt u -->

       <dt>A start tag whose tag name is "a"

       <dd>
        <p>If the <a href="#list-of4">list of active formatting elements</a>
         contains an element whose tag name is "a" between the end of the
         list and the last marker on the list (or the start of the list if
         there is no marker on the list), then this is a <a
         href="#parse">parse error</a>; act as if an end tag with the tag
         name "a" had been seen, then remove that element from the <a
         href="#list-of4">list of active formatting elements</a> and the <a
         href="#stack">stack of open elements</a> if the end tag didn't
         already remove it (it might not have if the element is not <a
         href="#have-an0" title="has an element in table scope">in table
         scope</a>).</p>

        <p class=example>In the non-conforming stream
         <code>&lt;a&nbsp;href="a">a&lt;table>&lt;a&nbsp;href="b">b&lt;/table>x</code>,
         the first <code><a href="#a">a</a></code> element would be closed
         upon seeing the second one, and the "x" character would be inside a
         link to "b", not to "a". This is despite the fact that the outer
         <code><a href="#a">a</a></code> element is not in table scope
         (meaning that a regular <code>&lt;/a></code> end tag at the start of
         the table wouldn't close the outer <code><a href="#a">a</a></code>
         element).</p>

        <p><a href="#reconstruct">Reconstruct the active formatting
         elements</a>, if any.</p>

        <p><a href="#insert" title="insert an html element">Insert an HTML
         element</a> for the token. Add that element to the <a
         href="#list-of4">list of active formatting elements</a>.</p>

       <dt>A start tag whose tag name is one of: "b", "big", "em", "font",
        "i", "nobr", "s", "small", "strike", "strong", "tt", "u"

       <dd>
        <p><a href="#reconstruct">Reconstruct the active formatting
         elements</a>, if any.</p>

        <p><a href="#insert" title="insert an html element">Insert an HTML
         element</a> for the token. Add that element to the <a
         href="#list-of4">list of active formatting elements</a>.</p>

       <dt id=adoptionAgency>An end tag whose tag name is one of: "a", "b",
        "big", "em", "font", "i", "nobr", "s", "small", "strike", "strong",
        "tt", "u"

       <dd>
        <p>Follow these steps:</p>

        <ol>
         <li>
          <p>Let the <var title="">formatting element</var> be the last
           element in the <a href="#list-of4">list of active formatting
           elements</a> that:</p>

          <ul>
           <li>is between the end of the list and the last scope marker in
            the list, if any, or the start of the list otherwise, and

           <li>has the same tag name as the token.
          </ul>

          <p>If there is no such node, or, if that node is also in the <a
           href="#stack">stack of open elements</a> but the element is not <a
           href="#have-an" title="has an element in scope">in scope</a>, then
           this is a <a href="#parse">parse error</a>. Abort these steps. The
           token is ignored.</p>

          <p>Otherwise, if there is such a node, but that node is not in the
           <a href="#stack">stack of open elements</a>, then this is a <a
           href="#parse">parse error</a>; remove the element from the list,
           and abort these steps.</p>

          <p>Otherwise, there is a <var title="">formatting element</var> and
           that element is in <a href="#stack" title="stack of open
           elements">the stack</a> and is <a href="#have-an" title="has an
           element in scope">in scope</a>. If the element is not the <a
           href="#current4">current node</a>, this is a <a
           href="#parse">parse error</a>. In any case, proceed with the
           algorithm as written in the following steps.</p>

         <li>
          <p>Let the <var title="">furthest block</var> be the topmost node
           in the <a href="#stack">stack of open elements</a> that is lower
           in the stack than the <var title="">formatting element</var>, and
           is not an element in the <a href="#phrasing">phrasing</a> or <a
           href="#formatting">formatting</a> categories. There might not be
           one.

         <li>
          <p>If there is no <var title="">furthest block</var>, then the UA
           must skip the subsequent steps and instead just pop all the nodes
           from the bottom of the <a href="#stack">stack of open
           elements</a>, from the <a href="#current4">current node</a> up to
           the <var title="">formatting element</var>, and remove the <var
           title="">formatting element</var> from the <a
           href="#list-of4">list of active formatting elements</a>.

         <li>
          <p>Let the <var title="">common ancestor</var> be the element
           immediately above the <var title="">formatting element</var> in
           the <a href="#stack">stack of open elements</a>.

         <li>
          <p>If the <var title="">furthest block</var> has a parent node,
           then remove the <var title="">furthest block</var> from its parent
           node.

         <li>
          <p>Let a bookmark note the position of the <var title="">formatting
           element</var> in the <a href="#list-of4">list of active formatting
           elements</a> relative to the elements on either side of it in the
           list.

         <li>
          <p>Let <var title="">node</var> and <var title="">last node</var>
           be the <var title="">furthest block</var>. Follow these steps:</p>

          <ol>
           <li>Let <var title="">node</var> be the element immediately prior
            to <var title="">node</var> in the <a href="#stack">stack of open
            elements</a>.

           <li>If <var title="">node</var> is not in the <a
            href="#list-of4">list of active formatting elements</a>, then
            remove <var title="">node</var> from the <a href="#stack">stack
            of open elements</a> and then go back to step 1.

           <li>Otherwise, if <var title="">node</var> is the <var
            title="">formatting element</var>, then go to the next step in
            the overall algorithm.

           <li>Otherwise, if <var title="">last node</var> is the <var
            title="">furthest block</var>, then move the aforementioned
            bookmark to be immediately after the <var title="">node</var> in
            the <a href="#list-of4">list of active formatting elements</a>.

           <li>If <var title="">node</var> has any children, perform a
            shallow clone of <var title="">node</var>, replace the entry for
            <var title="">node</var> in the <a href="#list-of4">list of
            active formatting elements</a> with an entry for the clone,
            replace the entry for <var title="">node</var> in the <a
            href="#stack">stack of open elements</a> with an entry for the
            clone, and let <var title="">node</var> be the clone.

           <li>Insert <var title="">last node</var> into <var
            title="">node</var>, first removing it from its previous parent
            node if any.

           <li>Let <var title="">last node</var> be <var title="">node</var>.

           <li>Return to step 1 of this inner set of steps.
          </ol>

         <li>
          <p>Insert whatever <var title="">last node</var> ended up being in
           the previous step into the <var title="">common ancestor</var>
           node, first removing it from its previous parent node if any.

         <li>
          <p>Perform a shallow clone of the <var title="">formatting
           element</var>.

         <li>
          <p>Take all of the child nodes of the <var title="">furthest
           block</var> and append them to the clone created in the last step.

         <li>
          <p>Append that clone to the <var title="">furthest block</var>.

         <li>
          <p>Remove the <var title="">formatting element</var> from the <a
           href="#list-of4">list of active formatting elements</a>, and
           insert the clone into the <a href="#list-of4">list of active
           formatting elements</a> at the position of the aforementioned
           bookmark.

         <li>
          <p>Remove the <var title="">formatting element</var> from the <a
           href="#stack">stack of open elements</a>, and insert the clone
           into the <a href="#stack">stack of open elements</a> immediately
           after (i.e. in a more deeply nested position than) the position of
           the <var title="">furthest block</var> in that stack.

         <li>
          <p>Jump back to step 1 in this series of steps.
        </ol>

        <p class=note>The way these steps are defined, only elements in the
         <a href="#formatting">formatting</a> category ever get cloned by
         this algorithm.</p>
        <!--XXX
        <div class="example">
         <p class="big-issue">Need an example.</p>
        </div>
-->
        
        <p class=note>Because of the way this algorithm causes elements to
         change parents, it has been dubbed the "adoption agency algorithm"
         (in contrast with other possibly algorithms for dealing with
         misnested content, which included the "incest algorithm", the
         "secret affair algorithm", and the "Heisenberg algorithm").</p>

       <dt>A start tag token whose tag name is "button"

       <dd>
        <p>If the <a href="#stack">stack of open elements</a> <a
         href="#have-an" title="has an element in scope">has a
         <code>button</code> element in scope</a>, then this is a <a
         href="#parse">parse error</a>; act as if an end tag with the tag
         name "button" had been seen, then reprocess the token.</p>

        <p>Otherwise:</p>

        <p><a href="#reconstruct">Reconstruct the active formatting
         elements</a>, if any.</p>

        <p><a href="#insert">Insert an HTML element</a> for the token.</p>

        <p>Insert a marker at the end of the <a href="#list-of4">list of
         active formatting elements</a>.</p>

       <dt>A start tag token whose tag name is one of: "marquee", "object"

       <dd>
        <p><a href="#reconstruct">Reconstruct the active formatting
         elements</a>, if any.</p>

        <p><a href="#insert">Insert an HTML element</a> for the token.</p>

        <p>Insert a marker at the end of the <a href="#list-of4">list of
         active formatting elements</a>.</p>

       <dt>An end tag token whose tag name is one of: "button", "marquee",
        "object"

       <dd>
        <p>If the <a href="#stack">stack of open elements</a> <a
         href="#have-an" title="has an element in scope">has in scope</a> an
         element whose tag name is the same as the tag name of the token,
         then <a href="#generate">generate implied end tags</a>.</p>

        <p>Now, if the <a href="#current4">current node</a> is not an element
         with the same tag name as the token, then this is a <a
         href="#parse">parse error</a>.</p>

        <p>Now, if the <a href="#stack">stack of open elements</a> <a
         href="#have-an">has an element in scope</a> whose tag name matches
         the tag name of the token, then pop elements from the stack until
         that element has been popped from the stack, and <a
         href="#clear0">clear the list of active formatting elements up to
         the last marker</a>.</p>

       <dt>A start tag token whose tag name is "xmp"

       <dd>
        <p><a href="#reconstruct">Reconstruct the active formatting
         elements</a>, if any.</p>

        <p><a href="#insert">Insert an HTML element</a> for the token.</p>

        <p>Switch the <a href="#content2">content model flag</a> to the CDATA
         state.</p>

       <dt>A start tag whose tag name is "table"

       <dd>
        <p>If the <a href="#stack">stack of open elements</a> <a
         href="#have-an" title="has an element in scope">has a <code>p</code>
         element in scope</a>, then act as if an end tag with the tag name
         <code><a href="#p">p</a></code> had been seen.</p>
        <!-- XXX quirks: don't do this -->
        <p><a href="#insert">Insert an HTML element</a> for the token.</p>

        <p>Change the <a href="#insertion0">insertion mode</a> to "<a
         href="#in-table" title="insertion mode: in table">in table</a>".</p>

       <dt>A start tag whose tag name is one of: "area", "basefont",
        "bgsound", "br", "embed", "img", "param", "spacer", "wbr"

       <dd>
        <p><a href="#reconstruct">Reconstruct the active formatting
         elements</a>, if any.</p>

        <p><a href="#insert" title="insert an html element">Insert an HTML
         element</a> for the token. Immediately pop the <a
         href="#current4">current node</a> off the <a href="#stack">stack of
         open elements</a>.</p>

       <dt>A start tag whose tag name is "hr"

       <dd>
        <p>If the <a href="#stack">stack of open elements</a> <a
         href="#have-an" title="has an element in scope">has a <code>p</code>
         element in scope</a>, then act as if an end tag with the tag name
         <code><a href="#p">p</a></code> had been seen.</p>
        <!-- XXX quirks: don't do this -->
        <p><a href="#insert" title="insert an html element">Insert an HTML
         element</a> for the token. Immediately pop the <a
         href="#current4">current node</a> off the <a href="#stack">stack of
         open elements</a>.</p>

       <dt>A start tag whose tag name is "image"

       <dd>
        <p><a href="#parse">Parse error</a>. Change the token's tag name to
         "img" and reprocess it. (Don't ask.)</p>
        <!-- As of
        2005-12, studies showed that around 0.2% of pages used the
        <image> element. -->
        

       <dt>A start tag whose tag name is "input"

       <dd>
        <p><a href="#reconstruct">Reconstruct the active formatting
         elements</a>, if any.</p>

        <p><a href="#insert" title="insert an html element">Insert an
         <code>input</code> element</a> for the token.</p>

        <p>If the <a href="#form-element"><code title="">form</code> element
         pointer</a> is not null, then <span>associate</span><!--XXX
        xref! -->
         the <code>input</code> element with the <code>form</code> element
         pointed to by the <a href="#form-element"><code title="">form</code>
         element pointer</a>.</p>

        <p>Pop that <code>input</code> element off the <a href="#stack">stack
         of open elements</a>.</p>

       <dt id=isindex>A start tag whose tag name is "isindex"

       <dd>
        <p><a href="#parse">Parse error</a>.</p>

        <p>If the <a href="#form-element"><code title="">form</code> element
         pointer</a> is not null, then ignore the token.</p>

        <p>Otherwise:</p>

        <p>Act as if a start tag token with the tag name "form" had been
         seen.</p>

        <p>Act as if a start tag token with the tag name "hr" had been seen.</p>

        <p>Act as if a start tag token with the tag name "p" had been seen.</p>

        <p>Act as if a start tag token with the tag name "label" had been
         seen.</p>

        <p>Act as if a stream of character tokens had been seen (see below
         for what they should say).</p>

        <p>Act as if a start tag token with the tag name "input" had been
         seen, with all the attributes from the "isindex" token, except with
         the "name" attribute set to the value "isindex" (ignoring any
         explicit "name" attribute).</p>

        <p>Act as if a stream of character tokens had been seen (see below
         for what they should say).</p>

        <p>Act as if an end tag token with the tag name "label" had been
         seen.</p>

        <p>Act as if an end tag token with the tag name "p" had been seen.</p>

        <p>Act as if a start tag token with the tag name "hr" had been seen.</p>

        <p>Act as if an end tag token with the tag name "form" had been seen.</p>

        <p>The two streams of character tokens together should, together with
         the <code>input</code> element, express the equivalent of "This is a
         searchable index. Insert your search keywords here: (input field)"
         in the user's preferred language.</p>

        <p class=big-issue> Then need to specify that if the form submission
         causes just a single form control, whose name is "isindex", to be
         submitted, then we submit just the value part, not the "isindex="
         part.</p>
       </dd>
       <!-- XXX keygen support; don't forget form element pointer!

       <dt>A start tag whose tag name is "keygen"</dt>
       <dd>
        ...
       </dd>
-->

       <dt>A start tag whose tag name is "textarea"

       <dd>
        <p><a href="#create">Create an element for the token</a>.</p>

        <p>If the <a href="#form-element"><code title="">form</code> element
         pointer</a> is not null, then <span>associate</span><!--XXX
        xref! -->
         the <code>textarea</code> element with the <code>form</code> element
         pointed to by the <a href="#form-element"><code title="">form</code>
         element pointer</a>.</p>

        <p>Append the new element to the <a href="#current4">current
         node</a>.</p>

        <p>Switch the tokeniser's <a href="#content2">content model flag</a>
         to the RCDATA state.</p>

        <p>If the next token is a U+000A LINE FEED (LF) character token, then
         ignore that token and move on to the next one. (Newlines at the
         start of <code>textarea</code> elements are ignored as an authoring
         convenience.)</p>

        <p>Then, collect all the character tokens that the tokeniser returns
         until it returns a token that is not a character token, or until it
         stops tokenising.</p>

        <p>If this process resulted in a collection of character tokens,
         append a single <code>Text</code> node, whose contents is the
         concatenation of all those tokens' characters, to the new element
         node.</p>

        <p>The tokeniser's <a href="#content2">content model flag</a> will
         have switched back to the PCDATA state.</p>

        <p>If the next token is an end tag token with the tag name
         "textarea", ignore it. Otherwise, this is a <a href="#parse">parse
         error</a>.</p>

       <dt>A start tag whose tag name is one of: "iframe", "noembed",
        "noframes"

       <dt>A start tag whose tag name is "noscript", if <a
        href="#scripting2">scripting is enabled</a>:

       <dd>
        <p><a href="#create">Create an element for the token</a>.</p>

        <p>For "iframe" tags, the node must be an <code><a
         href="#htmliframeelement">HTMLIFrameElement</a></code> object, for
         the other tags it must be an <code><a
         href="#htmlelement">HTMLElement</a></code> object.</p>

        <p>Append the new element to the <a href="#current4">current
         node</a>.</p>

        <p>Switch the tokeniser's <a href="#content2">content model flag</a>
         to the CDATA state.</p>

        <p>Then, collect all the character tokens that the tokeniser returns
         until it returns a token that is not a character token, or until it
         stops tokenising.</p>

        <p>If this process resulted in a collection of character tokens,
         append a single <code>Text</code> node, whose contents is the
         concatenation of all those tokens' characters, to the new element
         node.</p>

        <p>The tokeniser's <a href="#content2">content model flag</a> will
         have switched back to the PCDATA state.</p>

        <p>If the next token is an end tag token with the same tag name as
         the start tag token, ignore it. Otherwise, this is a <a
         href="#parse">parse error</a>.</p>

       <dt>A start tag whose tag name is "select"

       <dd>
        <p><a href="#reconstruct">Reconstruct the active formatting
         elements</a>, if any.</p>

        <p><a href="#insert">Insert an HTML element</a> for the token.</p>

        <p>Change the <a href="#insertion0">insertion mode</a> to "<a
         href="#in-select" title="insertion mode: in select">in select</a>".</p>
       </dd>
       <!-- XXX quirks:
       <dt>An end tag whose tag name is "br"</dt>
       <dd>
        <p>Act as if a start tag token with the tag name "br" had been
        seen. Ignore the end tag token.</p>
       </dd>
-->

       <dt>A start or end tag whose tag name is one of: "caption", "col",
        "colgroup", "frame", "frameset", "head", "option", "optgroup",
        "tbody", "td", "tfoot", "th", "thead", "tr"

       <dt>An end tag whose tag name is one of: "area", "basefont",
        "bgsound", <!--XXX quirks: remove br-->"br", "embed", "hr", "iframe",
        "image", "img", "input", "isindex", "noembed", "noframes", "param",
        "select", "spacer", "table", "textarea", "wbr"</dt>
       <!-- add keygen if we add the start tag -->

       <dt>An end tag whose tag name is "noscript", if <a
        href="#scripting2">scripting is enabled</a>:

       <dd>
        <p><a href="#parse">Parse error</a>. Ignore the token.</p>

       <dt>A start or end tag whose tag name is one of: "event-source",
        "section", "nav", "article", "aside", "header", "footer", "datagrid",
        "command"

       <dd> <!-- XXXX -->
        <p class=big-issue>Work in progress!</p>

       <dt>A start tag token not covered by the previous entries

       <dd>
        <p><a href="#reconstruct">Reconstruct the active formatting
         elements</a>, if any.</p>

        <p><a href="#insert">Insert an HTML element</a> for the token.</p>

        <p class=note>This element will be a <a href="#phrasing">phrasing</a>
         element.</p>
        <!--
Put the following into the MathML namespace if parsed:
   math, mrow, mfrac, msqrt, mroot, mstyle, merror, mpadded, 
   mphantom, mfenced, menclose, msub, msup, msubsup, munder, 
   mover, munderover, mmultiscripts, mtable, mlabeledtr, mtr, 
   mtd, maction
-->
        

       <dt>An end tag token not covered by the previous entries

       <dd>
        <p>Run the following algorithm:</p>

        <ol>
         <li>
          <p>Initialise <var title="">node</var> to be the <a
           href="#current4">current node</a> (the bottommost node of the
           stack).

         <li>
          <p>If <var title="">node</var> has the same tag name as the end tag
           token, then:</p>

          <ol>
           <li>
            <p><a href="#generate">Generate implied end tags</a>.

           <li>
            <p>If the tag name of the end tag token does not match the tag
             name of the <a href="#current4">current node</a>, this is a <a
             href="#parse">parse error</a>.

           <li>
            <p>Pop all the nodes from the <a href="#current4">current
             node</a> up to <var title="">node</var>, including <var
             title="">node</var>, then stop this algorithm.
          </ol>

         <li>
          <p>Otherwise, if <var title="">node</var> is in neither the <a
           href="#formatting">formatting</a> category nor the <a
           href="#phrasing">phrasing</a> category, then this is a <a
           href="#parse">parse error</a>. Stop this algorithm. The end tag
           token is ignored.

         <li>
          <p>Set <var title="">node</var> to the previous entry in the <a
           href="#stack">stack of open elements</a>.

         <li>
          <p>Return to step 2.
        </ol>
      </dl>

     <dt id=parsing-main-intable>If the <a href="#insertion0">insertion
      mode</a> is "<dfn id=in-table title="insertion mode: in table">in
      table</dfn>"

     <dd>
      <dl class=switch>
       <dt>A character token that is one of one of U+0009 CHARACTER
        TABULATION, U+000A LINE FEED (LF), U+000B LINE TABULATION, U+000C
        FORM FEED (FF), U+000D CARRIAGE RETURN (CR), or U+0020 SPACE

       <dd>
        <p><a href="#append" title="append a character">Append the
         character</a> to the <a href="#current4">current node</a>.</p>

       <dt>A comment token

       <dd>
        <p>Append a <code>Comment</code> node to the <a
         href="#current4">current node</a> with the <code
         title="">data</code> attribute set to the data given in the comment
         token.</p>

       <dt>A start tag whose tag name is "caption"

       <dd>
        <p><a href="#clear1">Clear the stack back to a table context</a>.
         (See below.)</p>

        <p>Insert a marker at the end of the <a href="#list-of4">list of
         active formatting elements</a>.</p>

        <p><a href="#insert">Insert an HTML element</a> for the token, then
         switch the <a href="#insertion0">insertion mode</a> to "<a
         href="#in-caption" title="insertion mode: in caption">in
         caption</a>".</p>

       <dt>A start tag whose tag name is "colgroup"

       <dd>
        <p><a href="#clear1">Clear the stack back to a table context</a>.
         (See below.)</p>

        <p><a href="#insert">Insert an HTML element</a> for the token, then
         switch the <a href="#insertion0">insertion mode</a> to "<a
         href="#in-column" title="insertion mode: in column group">in column
         group</a>".</p>

       <dt>A start tag whose tag name is "col"

       <dd>
        <p>Act as if a start tag token with the tag name "colgroup" had been
         seen, then reprocess the current token.</p>

       <dt>A start tag whose tag name is one of: "tbody", "tfoot", "thead"

       <dd>
        <p><a href="#clear1">Clear the stack back to a table context</a>.
         (See below.)</p>

        <p><a href="#insert">Insert an HTML element</a> for the token, then
         switch the <a href="#insertion0">insertion mode</a> to "<a
         href="#in-table0" title="insertion mode: in table body">in table
         body</a>".</p>

       <dt>A start tag whose tag name is one of: "td", "th", "tr"

       <dd>
        <p>Act as if a start tag token with the tag name "tbody" had been
         seen, then reprocess the current token.</p>

       <dt>A start tag whose tag name is "table"

       <dd>
        <p><a href="#parse">Parse error</a>. Act as if an end tag token with
         the tag name "table" had been seen, then, if that token wasn't
         ignored, reprocess the current token.</p>

        <p class=note>The fake end tag token here can only be ignored in the
         <a href="#innerhtml1"><code>innerHTML</code> case</a>.</p>

       <dt>An end tag whose tag name is "table"

       <dd>
        <p>If the <a href="#stack">stack of open elements</a> does not <a
         href="#have-an0" title="has an element in table scope">have an
         element in table scope</a> with the same tag name as the token, this
         is a <a href="#parse">parse error</a>. Ignore the token. (<a
         href="#innerhtml1"><code>innerHTML</code> case</a>)</p>

        <p>Otherwise:</p>

        <p><a href="#generate">Generate implied end tags</a>.</p>

        <p>Now, if the <a href="#current4">current node</a> is not a <code><a
         href="#table">table</a></code> element, then this is a <a
         href="#parse">parse error</a>.</p>

        <p>Pop elements from this stack until a <code><a
         href="#table">table</a></code> element has been popped from the
         stack.</p>

        <p><a href="#reset">Reset the insertion mode appropriately</a>.</p>

       <dt>An end tag whose tag name is one of: "body", "caption", "col",
        "colgroup", "html", "tbody", "td", "tfoot", "th", "thead", "tr"

       <dd>
        <p><a href="#parse">Parse error</a>. Ignore the token.</p>

       <dt>Anything else

       <dd>
        <p><a href="#parse">Parse error</a>. Process the token as if the <a
         href="#insertion0">insertion mode</a> was "<a href="#in-body"
         title="insertion mode: in body">in body</a>", with the following
         exception:</p>

        <p>If the <a href="#current4">current node</a> is a <code><a
         href="#table">table</a></code>, <code><a
         href="#tbody">tbody</a></code>, <code><a
         href="#tfoot0">tfoot</a></code>, <code><a
         href="#thead0">thead</a></code>, or <code><a
         href="#tr">tr</a></code> element, then, whenever a node would be
         inserted into the <a href="#current4">current node</a>, it must
         instead be inserted into the <em><a href="#foster">foster parent
         element</a></em>.</p>

        <p>The <dfn id=foster>foster parent element</dfn> is the parent
         element of the last <code><a href="#table">table</a></code> element
         in the <a href="#stack">stack of open elements</a>, if there is a
         <code><a href="#table">table</a></code> element and it has such a
         parent element. If there is no <code><a
         href="#table">table</a></code> element in the <a href="#stack">stack
         of open elements</a> (<a href="#innerhtml1"><code>innerHTML</code>
         case</a>), then the <em><a href="#foster">foster parent
         element</a></em> is the first element in the <a href="#stack">stack
         of open elements</a> (the <code><a href="#html">html</a></code>
         element). Otherwise, if there is a <code><a
         href="#table">table</a></code> element in the <a href="#stack">stack
         of open elements</a>, but the last <code><a
         href="#table">table</a></code> element in the <a href="#stack">stack
         of open elements</a> has no parent, or its parent node is not an
         element, then the <em><a href="#foster">foster parent
         element</a></em> is the element before the last <code><a
         href="#table">table</a></code> element in the <a href="#stack">stack
         of open elements</a>.</p>

        <p>If the <em><a href="#foster">foster parent element</a></em> is the
         parent element of the last <code><a href="#table">table</a></code>
         element in the <a href="#stack">stack of open elements</a>, then the
         new node must be inserted immediately <em>before</em> the last
         <code><a href="#table">table</a></code> element in the <a
         href="#stack">stack of open elements</a> in the <a
         href="#foster">foster parent element</a>; otherwise, the new node
         must be <em>appended</em> to the <a href="#foster">foster parent
         element</a>.</p>
      </dl>

      <p>When the steps above require the UA to <dfn id=clear1>clear the
       stack back to a table context</dfn>, it means that the UA must, while
       the <a href="#current4">current node</a> is not a <code><a
       href="#table">table</a></code> element or an <code><a
       href="#html">html</a></code> element, pop elements from the <a
       href="#stack">stack of open elements</a>. If this causes any elements
       to be popped from the stack, then this is a <a href="#parse">parse
       error</a>.</p>

      <p class=note>The <a href="#current4">current node</a> being an
       <code><a href="#html">html</a></code> element after this process is an
       <a href="#innerhtml1"><code>innerHTML</code> case</a>.</p>

     <dt id=parsing-main-incaption>If the <a href="#insertion0">insertion
      mode</a> is "<dfn id=in-caption title="insertion mode: in caption">in
      caption</dfn>"

     <dd>
      <dl class=switch>
       <dt>An end tag whose tag name is "caption"

       <dd>
        <p>If the <a href="#stack">stack of open elements</a> does not <a
         href="#have-an0" title="has an element in table scope">have an
         element in table scope</a> with the same tag name as the token, this
         is a <a href="#parse">parse error</a>. Ignore the token. (<a
         href="#innerhtml1"><code>innerHTML</code> case</a>)</p>

        <p>Otherwise:</p>

        <p><a href="#generate">Generate implied end tags</a>.</p>

        <p>Now, if the <a href="#current4">current node</a> is not a <code><a
         href="#caption0">caption</a></code> element, then this is a <a
         href="#parse">parse error</a>.</p>

        <p>Pop elements from this stack until a <code><a
         href="#caption0">caption</a></code> element has been popped from the
         stack.</p>

        <p><a href="#clear0">Clear the list of active formatting elements up
         to the last marker</a>.</p>

        <p>Switch the <a href="#insertion0">insertion mode</a> to "<a
         href="#in-table" title="insertion mode: in table">in table</a>".</p>

       <dt>A start tag whose tag name is one of: "caption", "col",
        "colgroup", "tbody", "td", "tfoot", "th", "thead", "tr"

       <dt>An end tag whose tag name is "table"

       <dd>
        <p><a href="#parse">Parse error</a>. Act as if an end tag with the
         tag name "caption" had been seen, then, if that token wasn't
         ignored, reprocess the current token.</p>

        <p class=note>The fake end tag token here can only be ignored in the
         <a href="#innerhtml1"><code>innerHTML</code> case</a>.</p>

       <dt>An end tag whose tag name is one of: "body", "col", "colgroup",
        "html", "tbody", "td", "tfoot", "th", "thead", "tr"

       <dd>
        <p><a href="#parse">Parse error</a>. Ignore the token.</p>

       <dt>Anything else

       <dd>
        <p>Process the token as if the <a href="#insertion0">insertion
         mode</a> was "<a href="#in-body" title="insertion mode: in body">in
         body</a>".</p>
      </dl>

     <dt id=parsing-main-incolgroup>If the <a href="#insertion0">insertion
      mode</a> is "<dfn id=in-column title="insertion mode: in column
      group">in column group</dfn>"

     <dd>
      <dl class=switch>
       <dt>A character token that is one of one of U+0009 CHARACTER
        TABULATION, U+000A LINE FEED (LF), U+000B LINE TABULATION, U+000C
        FORM FEED (FF), U+000D CARRIAGE RETURN (CR), or U+0020 SPACE

       <dd>
        <p><a href="#append" title="append a character">Append the
         character</a> to the <a href="#current4">current node</a>.</p>

       <dt>A comment token

       <dd>
        <p>Append a <code>Comment</code> node to the <a
         href="#current4">current node</a> with the <code
         title="">data</code> attribute set to the data given in the comment
         token.</p>

       <dt>A start tag whose tag name is "col"

       <dd>
        <p><a href="#insert" title="insert an HTML element">Insert a
         <code>col</code> element</a> for the token. Immediately pop the <a
         href="#current4">current node</a> off the <a href="#stack">stack of
         open elements</a>.</p>

       <dt>An end tag whose tag name is "colgroup"

       <dd>
        <p>If the <a href="#current4">current node</a> is the root <code><a
         href="#html">html</a></code> element, then this is a <a
         href="#parse">parse error</a>, ignore the token. (<a
         href="#innerhtml1"><code>innerHTML</code> case</a>)</p>

        <p>Otherwise, pop the <a href="#current4">current node</a> (which
         will be a <code><a href="#colgroup">colgroup</a></code> element)
         from the <a href="#stack">stack of open elements</a>. Switch the <a
         href="#insertion0">insertion mode</a> to "<a href="#in-table"
         title="insertion mode: in table">in table</a>".</p>

       <dt>An end tag whose tag name is "col"

       <dd>
        <p><a href="#parse">Parse error</a>. Ignore the token.</p>

       <dt>Anything else

       <dd>
        <p>Act as if an end tag with the tag name "colgroup" had been seen,
         and then, if that token wasn't ignored, reprocess the current token.</p>

        <p class=note>The fake end tag token here can only be ignored in the
         <a href="#innerhtml1"><code>innerHTML</code> case</a>.</p>
      </dl>

     <dt id=parsing-main-intbody>If the <a href="#insertion0">insertion
      mode</a> is "<dfn id=in-table0 title="insertion mode: in table body">in
      table body</dfn>"

     <dd>
      <dl class=switch>
       <dt>A start tag whose tag name is "tr"

       <dd>
        <p><a href="#clear2">Clear the stack back to a table body
         context</a>. (See below.)</p>

        <p><a href="#insert" title="insert an HTML element">Insert a
         <code>tr</code> element</a> for the token, then switch the <a
         href="#insertion0">insertion mode</a> to "<a href="#in-row"
         title="insertion mode: in row">in row</a>".</p>

       <dt>A start tag whose tag name is one of: "th", "td"

       <dd>
        <p><a href="#parse">Parse error</a>. Act as if a start tag with the
         tag name "tr" had been seen, then reprocess the current token.</p>

       <dt>An end tag whose tag name is one of: "tbody", "tfoot", "thead"

       <dd>
        <p>If the <a href="#stack">stack of open elements</a> does not <a
         href="#have-an0" title="has an element in table scope">have an
         element in table scope</a> with the same tag name as the token, this
         is a <a href="#parse">parse error</a>. Ignore the token.</p>

        <p>Otherwise:</p>

        <p><a href="#clear2">Clear the stack back to a table body
         context</a>. (See below.)</p>

        <p>Pop the <a href="#current4">current node</a> from the <a
         href="#stack">stack of open elements</a>. Switch the <a
         href="#insertion0">insertion mode</a> to "<a href="#in-table"
         title="insertion mode: in table">in table</a>".</p>

       <dt>A start tag whose tag name is one of: "caption", "col",
        "colgroup", "tbody", "tfoot", "thead"

       <dt>An end tag whose tag name is "table"

       <dd>
        <p>If the <a href="#stack">stack of open elements</a> does not <a
         href="#have-an0" title="has an element in table scope">have a
         <code>tbody</code>, <code>thead</code>, or <code>tfoot</code>
         element in table scope</a>, this is a <a href="#parse">parse
         error</a>. Ignore the token. (<a
         href="#innerhtml1"><code>innerHTML</code> case</a>)</p>

        <p>Otherwise:</p>

        <p><a href="#clear2">Clear the stack back to a table body
         context</a>. (See below.)</p>

        <p>Act as if an end tag with the same tag name as the <a
         href="#current4">current node</a> ("tbody", "tfoot", or "thead") had
         been seen, then reprocess the current token.</p>

       <dt>An end tag whose tag name is one of: "body", "caption", "col",
        "colgroup", "html", "td", "th", "tr"

       <dd>
        <p><a href="#parse">Parse error</a>. Ignore the token.</p>

       <dt>Anything else

       <dd>
        <p>Process the token as if the <a href="#insertion0">insertion
         mode</a> was "<a href="#in-table" title="insertion mode: in
         table">in table</a>".</p>
      </dl>

      <p>When the steps above require the UA to <dfn id=clear2>clear the
       stack back to a table body context</dfn>, it means that the UA must,
       while the <a href="#current4">current node</a> is not a <code><a
       href="#tbody">tbody</a></code>, <code><a
       href="#tfoot0">tfoot</a></code>, <code><a
       href="#thead0">thead</a></code>, or <code><a
       href="#html">html</a></code> element, pop elements from the <a
       href="#stack">stack of open elements</a>. If this causes any elements
       to be popped from the stack, then this is a <a href="#parse">parse
       error</a>.</p>

      <p class=note>The <a href="#current4">current node</a> being an
       <code><a href="#html">html</a></code> element after this process is an
       <a href="#innerhtml1"><code>innerHTML</code> case</a>.</p>

     <dt id=parsing-main-intr>If the <a href="#insertion0">insertion mode</a>
      is "<dfn id=in-row title="insertion mode: in row">in row</dfn>"

     <dd>
      <dl class=switch>
       <dt>A start tag whose tag name is one of: "th", "td"

       <dd>
        <p><a href="#clear3">Clear the stack back to a table row context</a>.
         (See below.)</p>

        <p><a href="#insert" title="insert an HTML element">Insert an HTML
         element</a> for the token, then switch the <a
         href="#insertion0">insertion mode</a> to "<a href="#in-cell"
         title="insertion mode: in cell">in cell</a>".</p>

        <p>Insert a marker at the end of the <a href="#list-of4">list of
         active formatting elements</a>.</p>

       <dt>An end tag whose tag name is "tr"

       <dd>
        <p>If the <a href="#stack">stack of open elements</a> does not <a
         href="#have-an0" title="has an element in table scope">have an
         element in table scope</a> with the same tag name as the token, this
         is a <a href="#parse">parse error</a>. Ignore the token. (<a
         href="#innerhtml1"><code>innerHTML</code> case</a>)</p>

        <p>Otherwise:</p>

        <p><a href="#clear3">Clear the stack back to a table row context</a>.
         (See below.)</p>

        <p>Pop the <a href="#current4">current node</a> (which will be a
         <code><a href="#tr">tr</a></code> element) from the <a
         href="#stack">stack of open elements</a>. Switch the <a
         href="#insertion0">insertion mode</a> to "<a href="#in-table0"
         title="insertion mode: in table body">in table body</a>".</p>

       <dt>A start tag whose tag name is one of: "caption", "col",
        "colgroup", "tbody", "tfoot", "thead", "tr"

       <dt>An end tag whose tag name is "table"

       <dd>
        <p>Act as if an end tag with the tag name "tr" had been seen, then,
         if that token wasn't ignored, reprocess the current token.</p>

        <p class=note>The fake end tag token here can only be ignored in the
         <a href="#innerhtml1"><code>innerHTML</code> case</a>.</p>

       <dt>An end tag whose tag name is one of: "tbody", "tfoot", "thead"

       <dd>
        <p>If the <a href="#stack">stack of open elements</a> does not <a
         href="#have-an0" title="has an element in table scope">have an
         element in table scope</a> with the same tag name as the token, this
         is a <a href="#parse">parse error</a>. Ignore the token.</p>

        <p>Otherwise, act as if an end tag with the tag name "tr" had been
         seen, then reprocess the current token.</p>

       <dt>An end tag whose tag name is one of: "body", "caption", "col",
        "colgroup", "html", "td", "th"

       <dd>
        <p><a href="#parse">Parse error</a>. Ignore the token.</p>

       <dt>Anything else

       <dd>
        <p>Process the token as if the <a href="#insertion0">insertion
         mode</a> was "<a href="#in-table" title="insertion mode: in
         table">in table</a>".</p>
      </dl>

      <p>When the steps above require the UA to <dfn id=clear3>clear the
       stack back to a table row context</dfn>, it means that the UA must,
       while the <a href="#current4">current node</a> is not a <code><a
       href="#tr">tr</a></code> element or an <code><a
       href="#html">html</a></code> element, pop elements from the <a
       href="#stack">stack of open elements</a>. If this causes any elements
       to be popped from the stack, then this is a <a href="#parse">parse
       error</a>.</p>

      <p class=note>The <a href="#current4">current node</a> being an
       <code><a href="#html">html</a></code> element after this process is an
       <a href="#innerhtml1"><code>innerHTML</code> case</a>.</p>

     <dt id=parsing-main-intd>If the <a href="#insertion0">insertion mode</a>
      is "<dfn id=in-cell title="insertion mode: in cell">in cell</dfn>"

     <dd>
      <dl class=switch>
       <dt>An end tag whose tag name is one of: "td", "th"

       <dd>
        <p>If the <a href="#stack">stack of open elements</a> does not <a
         href="#have-an0" title="has an element in table scope">have an
         element in table scope</a> with the same tag name as that of the
         token, then this is a <a href="#parse">parse error</a> and the token
         must be ignored.</p>

        <p>Otherwise:</p>

        <p><a href="#generate">Generate implied end tags</a>, except for
         elements with the same tag name as the token.</p>

        <p>Now, if the <a href="#current4">current node</a> is not an element
         with the same tag name as the token, then this is a <a
         href="#parse">parse error</a>.</p>

        <p>Pop elements from this stack until an element with the same tag
         name as the token has been popped from the stack.</p>

        <p><a href="#clear0">Clear the list of active formatting elements up
         to the last marker</a>.</p>

        <p>Switch the <a href="#insertion0">insertion mode</a> to "<a
         href="#in-row" title="insertion mode: in row">in row</a>". (The <a
         href="#current4">current node</a> will be a <code><a
         href="#tr">tr</a></code> element at this point.)</p>

       <dt>A start tag whose tag name is one of: "caption", "col",
        "colgroup", "tbody", "td", "tfoot", "th", "thead", "tr"

       <dd>
        <p>If the <a href="#stack">stack of open elements</a> does
         <em>not</em> <a href="#have-an0" title="has an element in table
         scope">have a <code>td</code> or <code>th</code> element in table
         scope</a>, then this is a <a href="#parse">parse error</a>; ignore
         the token. (<a href="#innerhtml1"><code>innerHTML</code> case</a>)</p>

        <p>Otherwise, <a href="#close2">close the cell</a> (see below) and
         reprocess the current token.</p>

       <dt>An end tag whose tag name is one of: "body", "caption", "col",
        "colgroup", "html"

       <dd>
        <p><a href="#parse">Parse error</a>. Ignore the token.</p>

       <dt>An end tag whose tag name is one of: "table", "tbody", "tfoot",
        "thead", "tr"

       <dd>
        <p>If the <a href="#stack">stack of open elements</a> does not <a
         href="#have-an0" title="has an element in table scope">have an
         element in table scope</a> with the same tag name as that of the
         token (which can only happen for "tbody", "tfoot" and "thead", or,
         in the <a href="#innerhtml1"><code>innerHTML</code> case</a>), then
         this is a <a href="#parse">parse error</a> and the token must be
         ignored.</p>

        <p>Otherwise, <a href="#close2">close the cell</a> (see below) and
         reprocess the current token.</p>

       <dt>Anything else

       <dd>
        <p>Process the token as if the <a href="#insertion0">insertion
         mode</a> was "<a href="#in-body" title="insertion mode: in body">in
         body</a>".</p>
      </dl>

      <p>Where the steps above say to <dfn id=close2>close the cell</dfn>,
       they mean to follow the following algorithm:</p>

      <ol>
       <li>
        <p>If the <a href="#stack">stack of open elements</a> <a
         href="#have-an0" title="has an element in table scope">has a
         <code>td</code> element in table scope</a>, then act as if an end
         tag token with the tag name "td" had been seen.

       <li>
        <p>Otherwise, the <a href="#stack">stack of open elements</a> will <a
         href="#have-an0" title="has an element in table scope">have a
         <code>th</code> element in table scope</a>; act as if an end tag
         token with the tag name "th" had been seen.
      </ol>

      <p class=note>The <a href="#stack">stack of open elements</a> cannot
       have both a <code><a href="#td">td</a></code> and a <code><a
       href="#th">th</a></code> element <a href="#have-an0" title="has an
       element in table scope">in table scope</a> at the same time, nor can
       it have neither when the <a href="#insertion0">insertion mode</a> is
       "<a href="#in-cell" title="insertion mode: in cell">in cell</a>".</p>

     <dt id=parsing-main-inselect>If the <a href="#insertion0">insertion
      mode</a> is "<dfn id=in-select title="insertion mode: in select">in
      select</dfn>"

     <dd>
      <p>Handle the token as follows:</p>

      <dl class=switch>
       <dt>A character token

       <dd>
        <p><a href="#append" title="append a character">Append the token's
         character</a> to the <a href="#current4">current node</a>.</p>

       <dt>A comment token

       <dd>
        <p>Append a <code>Comment</code> node to the <a
         href="#current4">current node</a> with the <code
         title="">data</code> attribute set to the data given in the comment
         token.</p>

       <dt>A start tag token whose tag name is "option"

       <dd>
        <p>If the <a href="#current4">current node</a> is an
         <code>option</code> element, act as if an end tag with the tag name
         "option" had been seen.</p>

        <p><a href="#insert">Insert an HTML element</a> for the token.</p>

       <dt>A start tag token whose tag name is "optgroup"

       <dd>
        <p>If the <a href="#current4">current node</a> is an
         <code>option</code> element, act as if an end tag with the tag name
         "option" had been seen.</p>

        <p>If the <a href="#current4">current node</a> is an
         <code>optgroup</code> element, act as if an end tag with the tag
         name "optgroup" had been seen.</p>

        <p><a href="#insert">Insert an HTML element</a> for the token.</p>

       <dt>An end tag token whose tag name is "optgroup"

       <dd>
        <p>First, if the <a href="#current4">current node</a> is an
         <code>option</code> element, and the node immediately before it in
         the <a href="#stack">stack of open elements</a> is an
         <code>optgroup</code> element, then act as if an end tag with the
         tag name "option" had been seen.</p>

        <p>If the <a href="#current4">current node</a> is an
         <code>optgroup</code> element, then pop that node from the <a
         href="#stack">stack of open elements</a>. Otherwise, this is a <a
         href="#parse">parse error</a>, ignore the token.</p>

       <dt>An end tag token whose tag name is "option"

       <dd>
        <p>If the <a href="#current4">current node</a> is an
         <code>option</code> element, then pop that node from the <a
         href="#stack">stack of open elements</a>. Otherwise, this is a <a
         href="#parse">parse error</a>, ignore the token.</p>

       <dt>An end tag whose tag name is "select"

       <dd>
        <p>If the <a href="#stack">stack of open elements</a> does not <a
         href="#have-an0" title="has an element in table scope">have an
         element in table scope</a> with the same tag name as the token, this
         is a <a href="#parse">parse error</a>. Ignore the token. (<a
         href="#innerhtml1"><code>innerHTML</code> case</a>)</p>

        <p>Otherwise:</p>

        <p>Pop elements from the <a href="#stack">stack of open elements</a>
         until a <code>select</code> element has been popped from the stack.</p>

        <p><a href="#reset">Reset the insertion mode appropriately</a>.</p>

       <dt>A start tag whose tag name is "select"

       <dd>
        <p><a href="#parse">Parse error</a>. Act as if the token had been an
         end tag with the tag name "select" instead.</p>

       <dt>An end tag whose tag name is one of: "caption", "table", "tbody",
        "tfoot", "thead", "tr", "td", "th"

       <dd>
        <p><a href="#parse">Parse error</a>.</p>

        <p>If the <a href="#stack">stack of open elements</a> <a
         href="#have-an0">has an element in table scope</a> with the same tag
         name as that of the token, then act as if an end tag with the tag
         name "select" had been seen, and reprocess the token. Otherwise,
         ignore the token.</p>

       <dt>Anything else

       <dd>
        <p><a href="#parse">Parse error</a>. Ignore the token.</p>
      </dl>

     <dt id=parsing-main-afterbody>If the <a href="#insertion0">insertion
      mode</a> is "<dfn id=after2 title="insertion mode: after body">after
      body</dfn>"

     <dd>
      <p>Handle the token as follows:</p>

      <dl class=switch>
       <dt>A character token that is one of one of U+0009 CHARACTER
        TABULATION, U+000A LINE FEED (LF), U+000B LINE TABULATION, U+000C
        FORM FEED (FF), U+000D CARRIAGE RETURN (CR), or U+0020 SPACE

       <dd>
        <p>Process the token as it would be processed if the <a
         href="#insertion0">insertion mode</a> was "<a href="#in-body"
         title="insertion mode: in body">in body</a>".</p>

       <dt>A comment token

       <dd>
        <p>Append a <code>Comment</code> node to the first element in the <a
         href="#stack">stack of open elements</a> (the <code><a
         href="#html">html</a></code> element), with the <code
         title="">data</code> attribute set to the data given in the comment
         token.</p>

       <dt>An end tag with the tag name "html"

       <dd>
        <p>If the parser was originally created in order to handle the
         setting of <em>an element</em>'s <code title=dom-innerHTML-HTML><a
         href="#innerhtml0">innerHTML</a></code> attribute, this is a <a
         href="#parse">parse error</a>; ignore the token. (The element will
         be an <code><a href="#html">html</a></code> element in this case.)
         (<a href="#innerhtml1"><code>innerHTML</code> case</a>)</p>

        <p>Otherwise, switch to <a href="#the-trailing0">the trailing end
         phase</a>.</p>

       <dt>Anything else

       <dd>
        <p><a href="#parse">Parse error</a>. Set the <a
         href="#insertion0">insertion mode</a> to "<a href="#in-body"
         title="insertion mode: in body">in body</a>" and reprocess the
         token.</p>
      </dl>

     <dt id=parsing-main-inframeset>If the <a href="#insertion0">insertion
      mode</a> is "<dfn id=in-frameset title="insertion mode: in frameset">in
      frameset</dfn>"

     <dd>
      <p>Handle the token as follows:</p>

      <dl class=switch>
       <dt>A character token that is one of one of U+0009 CHARACTER
        TABULATION, U+000A LINE FEED (LF), U+000B LINE TABULATION, U+000C
        FORM FEED (FF), U+000D CARRIAGE RETURN (CR), or U+0020 SPACE

       <dd>
        <p><a href="#append" title="append a character">Append the
         character</a> to the <a href="#current4">current node</a>.</p>

       <dt>A comment token

       <dd>
        <p>Append a <code>Comment</code> node to the <a
         href="#current4">current node</a> with the <code
         title="">data</code> attribute set to the data given in the comment
         token.</p>

       <dt>A start tag with the tag name "frameset"

       <dd>
        <p><a href="#insert" title="Insert an HTML element">Insert a
         <code>frameset</code> element</a> for the token.</p>

       <dt>An end tag with the tag name "frameset"

       <dd>
        <p>If the <a href="#current4">current node</a> is the root <code><a
         href="#html">html</a></code> element, then this is a <a
         href="#parse">parse error</a>; ignore the token. (<a
         href="#innerhtml1"><code>innerHTML</code> case</a>)</p>

        <p>Otherwise, pop the <a href="#current4">current node</a> from the
         <a href="#stack">stack of open elements</a>.</p>

        <p>If the parser was <em>not</em> originally created in order to
         handle the setting of an element's <code title=dom-innerHTML-HTML><a
         href="#innerhtml0">innerHTML</a></code> attribute (<a
         href="#innerhtml1"><code>innerHTML</code> case</a>), and the <a
         href="#current4">current node</a> is no longer a
         <code>frameset</code> element, then change the <a
         href="#insertion0">insertion mode</a> to "<a href="#after3"
         title="insertion mode: after frameset">after frameset</a>".</p>

       <dt>A start tag with the tag name "frame"

       <dd>
        <p><a href="#insert">Insert an HTML element</a> for the token.
         Immediately pop the <a href="#current4">current node</a> off the <a
         href="#stack">stack of open elements</a>.</p>

       <dt>A start tag with the tag name "noframes"

       <dd>
        <p>Process the token as if the <a href="#insertion0">insertion
         mode</a> had been "<a href="#in-body" title="insertion mode: in
         body">in body</a>".</p>

       <dt>Anything else

       <dd>
        <p><a href="#parse">Parse error</a>. Ignore the token.</p>
      </dl>

     <dt id=parsing-main-afterframeset>If the <a href="#insertion0">insertion
      mode</a> is "<dfn id=after3 title="insertion mode: after
      frameset">after frameset</dfn>"

     <dd>
      <p>Handle the token as follows:</p>

      <dl class=switch>
       <dt>A character token that is one of one of U+0009 CHARACTER
        TABULATION, U+000A LINE FEED (LF), U+000B LINE TABULATION, U+000C
        FORM FEED (FF), U+000D CARRIAGE RETURN (CR), or U+0020 SPACE

       <dd>
        <p><a href="#append" title="append a character">Append the
         character</a> to the <a href="#current4">current node</a>.</p>

       <dt>A comment token

       <dd>
        <p>Append a <code>Comment</code> node to the <a
         href="#current4">current node</a> with the <code
         title="">data</code> attribute set to the data given in the comment
         token.</p>

       <dt>An end tag with the tag name "html"

       <dd>
        <p>Switch to <a href="#the-trailing0">the trailing end phase</a>.</p>

       <dt>A start tag with the tag name "noframes"

       <dd>
        <p>Process the token as if the <a href="#insertion0">insertion
         mode</a> had been "<a href="#in-body" title="insertion mode: in
         body">in body</a>".</p>

       <dt>Anything else

       <dd>
        <p><a href="#parse">Parse error</a>. Ignore the token.</p>
      </dl>
    </dl>
  </dl>

  <p class=big-issue>This doesn't handle UAs that don't support frames, or
   that do support frames but want to show the NOFRAMES content. Supporting
   the former is easy; supporting the latter is harder.

  <h5 id=the-trailing><span class=secno>8.2.4.4. </span><dfn
   id=the-trailing0>The trailing end phase</dfn></h5>

  <p>After <a href="#the-main0">the main phase</a>, as each token is emitted
   from the <a href="#tokenisation0">tokenisation</a> stage, it must be
   processed as described in this section.

  <dl class=switch>
   <dt>A DOCTYPE token

   <dd>
    <p><a href="#parse">Parse error</a>. Ignore the token.</p>

   <dt>A comment token

   <dd>
    <p>Append a <code>Comment</code> node to the <code>Document</code> object
     with the <code title="">data</code> attribute set to the data given in
     the comment token.</p>

   <dt>A character token that is one of one of U+0009 CHARACTER TABULATION,
    U+000A LINE FEED (LF), U+000B LINE TABULATION, U+000C FORM FEED (FF),
    U+000D CARRIAGE RETURN (CR), or U+0020 SPACE

   <dd>
    <p>Process the token as it would be processed in <a href="#the-main0">the
     main phase</a>.</p>

   <dt>A character token that is <em>not</em> one of U+0009 CHARACTER
    TABULATION, U+000A LINE FEED (LF), U+000B LINE TABULATION, U+000C FORM
    FEED (FF), U+000D CARRIAGE RETURN (CR), or U+0020 SPACE

   <dt>A start tag token

   <dt>An end tag token

   <dd>
    <p><a href="#parse">Parse error</a>. Switch back to <a
     href="#the-main0">the main phase</a> and reprocess the token.</p>

   <dt>An end-of-file token

   <dd>
    <p><a href="#stops">Stop parsing</a>.</p>
  </dl>

  <h4 id=the-end><span class=secno>8.2.5. </span>The End</h4>

  <p>Once the user agent <dfn id=stops title="stop parsing">stops
   parsing</dfn> the document, the user agent must follow the steps in this
   section.

  <p>First, <!--the user agent must <span title="fire a DOMContentLoaded
  event">fire a <code
  title="event-DOMContentLoaded">DOMContentLoaded</code> event</span>
  at <span>the <code>body</code> element</span>.</p>

  <p>Then, -->the
   rules for <a href="#when-a">when a script completes loading</a> start
   applying (script execution is no longer managed by the parser).

  <p>If any of the scripts in the <a href="#list-of1">list of scripts that
   will execute as soon as possible</a> have <span>completed
   loading</span><!-- XXX xref -->, or if the <a href="#list-of0">list of
   scripts that will execute asynchronously</a> is not empty and the first
   script in that list has <span>completed loading</span><!-- XXX xref
  -->,
   then the user agent must act as if those scripts just completed loading,
   following the rules given for that in the <code><a
   href="#script0">script</a></code> element definition.

  <p>Then, if the <a href="#list-of">list of scripts that will execute when
   the document has finished parsing</a> is not empty, and the first item in
   this list has already <span>completed loading</span><!--XXX
  xref -->,
   then the user agent must act as if that script just finished loading.

  <p>By this point, there will be no scripts that have loaded but have not
   yet been executed.

  <p>The user agent must then <a href="#firing2">fire a simple event</a>
   called <code title=event-DOMContentLoaded>DOMContentLoaded</code> at the
   <code>Document</code>.

  <p>Once everything that <dfn id=delays title="delay the load event">delays
   the load event</dfn> has completed, the user agent must <a href="#firing4"
   title="fire a load event">fire a <code title=event-load>load</code>
   event</a> at <a href="#the-body0">the <code>body</code> element</a>.</p>
  <!-- XXX make sure things "delay the load event" -->
  <!--XXX need to handle
http://lxr.mozilla.org/mozilla/source/parser/htmlparser/src/CNavDTD.cpp#2354
2354           // Don't open transient styles if it makes the stack deep, bug 58917.
-->
  <!--XXX
http://lxr.mozilla.org/mozilla/source/parser/htmlparser/src/nsHTMLTokenizer.cpp#749
-->
  <!--
see also  CTextToken::ConsumeCharacterData()  for CDATA parsing?

1212                      1  Here's a tricky case from bug 22596:  <h5><li><h5>
1213                         How do we know that the 2nd <h5> should close the <LI> rather than nest inside the <LI>?
1214                         (Afterall, the <h5> is a legal child of the <LI>).
1215               
1216                         The way you know is that there is no root between the two, so the <h5> binds more
1217                         tightly to the 1st <h5> than to the <LI>.
1218                      2.  Also, bug 6148 shows this case: <SPAN><DIV><SPAN>
1219                         From this case we learned not to execute this logic if the parent is a block.
1220                     
1221                      3. Fix for 26583
1222                         Ex. <A href=foo.html><B>foo<A href-bar.html>bar</A></B></A>  <- A legal HTML
1223                         In the above example clicking on "foo" or "bar" should link to
1224                         foo.html or bar.html respectively. That is, the inner <A> should be informed
1225                         about the presence of an open <A> above <B>..so that the inner <A> can close out
1226                         the outer <A>. The following code does it for us.
1227                      
1228                      4. Fix for 27865 [ similer to 22596 ]. Ex: <DL><DD><LI>one<DD><LI>two
 - http://lxr.mozilla.org/mozilla/source/parser/htmlparser/src/CNavDTD.cpp#1211

815             // Here's a problem.  If theTag is legal in here, we don't move it
816             // out.  So if we're moving stuff out of here, the parent of theTag
817             // gets closed at this point.  But some things are legal
818             // _everywhere_ and hence would effectively close out misplaced
819             // content in tables.  This is undesirable, so treat them as
820             // illegal here so they'll be shipped out with their parents and
821             // siblings.  See bug 40855 for an explanation (that bug was for
822             // comments, but the same issues arise with whitespace, newlines,
823             // noscript, etc).  Script is special, though.  Shipping it out
824             // breaks document.write stuff.  See bug 243064.
 - http://lxr.mozilla.org/mozilla/source/parser/htmlparser/src/CNavDTD.cpp#825


1326     /**************************************************************************************
1327      *
1328      * Now a little code to deal with bug #49687 (crash when layout stack gets too deep)
1329      * I've also opened this up to any container (not just inlines): re bug 55095
1330      * Improved to handle bug 55980 (infinite loop caused when DEPTH is exceeded and
1331      * </P> is encountered by itself (<P>) is continuously produced.
1332      *
1333      **************************************************************************************/

1912               // Oh boy!! we found a "stray" tag. Nav4.x and IE introduce line break in
1913               // such cases. So, let's simulate that effect for compatibility.
1914               // Ex. <html><body>Hello</P>There</body></html>
http://lxr.mozilla.org/mozilla/source/parser/htmlparser/src/CNavDTD.cpp#1912

http://lxr.mozilla.org/seamonkey/search?string=nested
/parser/htmlparser/src/CNavDTD.cpp, line 791 - * 2. <CENTER><DL><DT><A><CENTER> allow nested <CENTER>
/parser/htmlparser/src/CNavDTD.cpp, line 792 - * 3. <TABLE><TR><TD><TABLE>... allow nested <TABLE>
/parser/htmlparser/src/CNavDTD.cpp, line 2562 - // Discard nested forms - bug 72639
/parser/htmlparser/src/nsElementTable.cpp, line 1453 - * 2. <CENTER><DL><DT><A><CENTER> allow nested <CENTER>
/parser/htmlparser/src/nsElementTable.cpp, line 1454 - * 3. <TABLE><TR><TD><TABLE>... allow nested <TABLE>
/parser/htmlparser/src/nsElementTable.cpp, line 1901 - // Ex: <H1><LI><H1><LI>. Inner LI has the potential of getting nested
-->

  <h3 id=namespaces><span class=secno>8.3. </span>Namespaces</h3>

  <p>The <dfn id=html-namespace0>HTML namespace</dfn> is:
   <code>http://www.w3.org/1999/xhtml</code>

  <h3 id=entities><span class=secno>8.4. </span><dfn
   id=entities0>Entities</dfn></h3>

  <p>This table lists the entity names that are supported by HTML, and the
   code points to which they refer. It is referenced by the previous
   sections.</p>
  <!--XXX
 entities: 
 94         // If an entity value is greater than 255 then:
 95         // Nav 4.x does not treat it as an entity,
 96         // IE treats it as an entity if terminated with a semicolon.
 97         // Resembling IE!!
http://lxr.mozilla.org/mozilla/source/parser/htmlparser/src/nsHTMLTokens.cpp#94
-->

  <table>
   <thead>
    <tr>
     <th> Entity Name

     <th> Character

   <tbody>
    <tr>
     <td> <code title="">AElig</code>

     <td> U+00C6

    <tr>
     <td> <code title="">Aacute</code>

     <td> U+00C1

    <tr>
     <td> <code title="">Acirc</code>

     <td> U+00C2

    <tr>
     <td> <code title="">Agrave</code>

     <td> U+00C0

    <tr>
     <td> <code title="">Alpha</code>

     <td> U+0391

    <tr>
     <td> <code title="">Aring</code>

     <td> U+00C5

    <tr>
     <td> <code title="">Atilde</code>

     <td> U+00C3

    <tr>
     <td> <code title="">Auml</code>

     <td> U+00C4

    <tr>
     <td> <code title="">Beta</code>

     <td> U+0392

    <tr>
     <td> <code title="">Ccedil</code>

     <td> U+00C7

    <tr>
     <td> <code title="">Chi</code>

     <td> U+03A7

    <tr>
     <td> <code title="">Dagger</code>

     <td> U+2021

    <tr>
     <td> <code title="">Delta</code>

     <td> U+0394

    <tr>
     <td> <code title="">ETH</code>

     <td> U+00D0

    <tr>
     <td> <code title="">Eacute</code>

     <td> U+00C9

    <tr>
     <td> <code title="">Ecirc</code>

     <td> U+00CA

    <tr>
     <td> <code title="">Egrave</code>

     <td> U+00C8

    <tr>
     <td> <code title="">Epsilon</code>

     <td> U+0395

    <tr>
     <td> <code title="">Eta</code>

     <td> U+0397

    <tr>
     <td> <code title="">Euml</code>

     <td> U+00CB

    <tr>
     <td> <code title="">Gamma</code>

     <td> U+0393

    <tr>
     <td> <code title="">Iacute</code>

     <td> U+00CD

    <tr>
     <td> <code title="">Icirc</code>

     <td> U+00CE

    <tr>
     <td> <code title="">Igrave</code>

     <td> U+00CC

    <tr>
     <td> <code title="">Iota</code>

     <td> U+0399

    <tr>
     <td> <code title="">Iuml</code>

     <td> U+00CF

    <tr>
     <td> <code title="">Kappa</code>

     <td> U+039A

    <tr>
     <td> <code title="">Lambda</code>

     <td> U+039B

    <tr>
     <td> <code title="">Mu</code>

     <td> U+039C

    <tr>
     <td> <code title="">Ntilde</code>

     <td> U+00D1

    <tr>
     <td> <code title="">Nu</code>

     <td> U+039D

    <tr>
     <td> <code title="">OElig</code>

     <td> U+0152

    <tr>
     <td> <code title="">Oacute</code>

     <td> U+00D3

    <tr>
     <td> <code title="">Ocirc</code>

     <td> U+00D4

    <tr>
     <td> <code title="">Ograve</code>

     <td> U+00D2

    <tr>
     <td> <code title="">Omega</code>

     <td> U+03A9

    <tr>
     <td> <code title="">Omicron</code>

     <td> U+039F

    <tr>
     <td> <code title="">Oslash</code>

     <td> U+00D8

    <tr>
     <td> <code title="">Otilde</code>

     <td> U+00D5

    <tr>
     <td> <code title="">Ouml</code>

     <td> U+00D6

    <tr>
     <td> <code title="">Phi</code>

     <td> U+03A6

    <tr>
     <td> <code title="">Pi</code>

     <td> U+03A0

    <tr>
     <td> <code title="">Prime</code>

     <td> U+2033

    <tr>
     <td> <code title="">Psi</code>

     <td> U+03A8

    <tr>
     <td> <code title="">Rho</code>

     <td> U+03A1

    <tr>
     <td> <code title="">Scaron</code>

     <td> U+0160

    <tr>
     <td> <code title="">Sigma</code>

     <td> U+03A3

    <tr>
     <td> <code title="">THORN</code>

     <td> U+00DE

    <tr>
     <td> <code title="">Tau</code>

     <td> U+03A4

    <tr>
     <td> <code title="">Theta</code>

     <td> U+0398

    <tr>
     <td> <code title="">Uacute</code>

     <td> U+00DA

    <tr>
     <td> <code title="">Ucirc</code>

     <td> U+00DB

    <tr>
     <td> <code title="">Ugrave</code>

     <td> U+00D9

    <tr>
     <td> <code title="">Upsilon</code>

     <td> U+03A5

    <tr>
     <td> <code title="">Uuml</code>

     <td> U+00DC

    <tr>
     <td> <code title="">Xi</code>

     <td> U+039E

    <tr>
     <td> <code title="">Yacute</code>

     <td> U+00DD

    <tr>
     <td> <code title="">Yuml</code>

     <td> U+0178

    <tr>
     <td> <code title="">Zeta</code>

     <td> U+0396

    <tr>
     <td> <code title="">aacute</code>

     <td> U+00E1

    <tr>
     <td> <code title="">acirc</code>

     <td> U+00E2

    <tr>
     <td> <code title="">acute</code>

     <td> U+00B4

    <tr>
     <td> <code title="">aelig</code>

     <td> U+00E6

    <tr>
     <td> <code title="">agrave</code>

     <td> U+00E0

    <tr>
     <td> <code title="">alefsym</code>

     <td> U+2135

    <tr>
     <td> <code title="">alpha</code>

     <td> U+03B1

    <tr>
     <td> <code title="">amp</code>

     <td> U+0026

    <tr>
     <td> <code title="">AMP</code>

     <td> U+0026

    <tr>
     <td> <code title="">and</code>

     <td> U+2227

    <tr>
     <td> <code title="">ang</code>

     <td> U+2220

    <tr>
     <td> <code title="">apos</code>

     <td> U+0027

    <tr>
     <td> <code title="">aring</code>

     <td> U+00E5

    <tr>
     <td> <code title="">asymp</code>

     <td> U+2248

    <tr>
     <td> <code title="">atilde</code>

     <td> U+00E3

    <tr>
     <td> <code title="">auml</code>

     <td> U+00E4

    <tr>
     <td> <code title="">bdquo</code>

     <td> U+201E

    <tr>
     <td> <code title="">beta</code>

     <td> U+03B2

    <tr>
     <td> <code title="">brvbar</code>

     <td> U+00A6

    <tr>
     <td> <code title="">bull</code>

     <td> U+2022

    <tr>
     <td> <code title="">cap</code>

     <td> U+2229

    <tr>
     <td> <code title="">ccedil</code>

     <td> U+00E7

    <tr>
     <td> <code title="">cedil</code>

     <td> U+00B8

    <tr>
     <td> <code title="">cent</code>

     <td> U+00A2

    <tr>
     <td> <code title="">chi</code>

     <td> U+03C7

    <tr>
     <td> <code title="">circ</code>

     <td> U+02C6

    <tr>
     <td> <code title="">clubs</code>

     <td> U+2663

    <tr>
     <td> <code title="">cong</code>

     <td> U+2245

    <tr>
     <td> <code title="">copy</code>

     <td> U+00A9

    <tr>
     <td> <code title="">COPY</code>

     <td> U+00A9

    <tr>
     <td> <code title="">crarr</code>

     <td> U+21B5

    <tr>
     <td> <code title="">cup</code>

     <td> U+222A

    <tr>
     <td> <code title="">curren</code>

     <td> U+00A4

    <tr>
     <td> <code title="">dArr</code>

     <td> U+21D3

    <tr>
     <td> <code title="">dagger</code>

     <td> U+2020

    <tr>
     <td> <code title="">darr</code>

     <td> U+2193

    <tr>
     <td> <code title="">deg</code>

     <td> U+00B0

    <tr>
     <td> <code title="">delta</code>

     <td> U+03B4

    <tr>
     <td> <code title="">diams</code>

     <td> U+2666

    <tr>
     <td> <code title="">divide</code>

     <td> U+00F7

    <tr>
     <td> <code title="">eacute</code>

     <td> U+00E9

    <tr>
     <td> <code title="">ecirc</code>

     <td> U+00EA

    <tr>
     <td> <code title="">egrave</code>

     <td> U+00E8

    <tr>
     <td> <code title="">empty</code>

     <td> U+2205

    <tr>
     <td> <code title="">emsp</code>

     <td> U+2003

    <tr>
     <td> <code title="">ensp</code>

     <td> U+2002

    <tr>
     <td> <code title="">epsilon</code>

     <td> U+03B5

    <tr>
     <td> <code title="">equiv</code>

     <td> U+2261

    <tr>
     <td> <code title="">eta</code>

     <td> U+03B7

    <tr>
     <td> <code title="">eth</code>

     <td> U+00F0

    <tr>
     <td> <code title="">euml</code>

     <td> U+00EB

    <tr>
     <td> <code title="">euro</code>

     <td> U+20AC

    <tr>
     <td> <code title="">exist</code>

     <td> U+2203

    <tr>
     <td> <code title="">fnof</code>

     <td> U+0192

    <tr>
     <td> <code title="">forall</code>

     <td> U+2200

    <tr>
     <td> <code title="">frac12</code>

     <td> U+00BD

    <tr>
     <td> <code title="">frac14</code>

     <td> U+00BC

    <tr>
     <td> <code title="">frac34</code>

     <td> U+00BE

    <tr>
     <td> <code title="">frasl</code>

     <td> U+2044

    <tr>
     <td> <code title="">gamma</code>

     <td> U+03B3

    <tr>
     <td> <code title="">ge</code>

     <td> U+2265

    <tr>
     <td> <code title="">gt</code>

     <td> U+003E

    <tr>
     <td> <code title="">GT</code>

     <td> U+003E

    <tr>
     <td> <code title="">hArr</code>

     <td> U+21D4

    <tr>
     <td> <code title="">harr</code>

     <td> U+2194

    <tr>
     <td> <code title="">hearts</code>

     <td> U+2665

    <tr>
     <td> <code title="">hellip</code>

     <td> U+2026

    <tr>
     <td> <code title="">iacute</code>

     <td> U+00ED

    <tr>
     <td> <code title="">icirc</code>

     <td> U+00EE

    <tr>
     <td> <code title="">iexcl</code>

     <td> U+00A1

    <tr>
     <td> <code title="">igrave</code>

     <td> U+00EC

    <tr>
     <td> <code title="">image</code>

     <td> U+2111

    <tr>
     <td> <code title="">infin</code>

     <td> U+221E

    <tr>
     <td> <code title="">int</code>

     <td> U+222B

    <tr>
     <td> <code title="">iota</code>

     <td> U+03B9

    <tr>
     <td> <code title="">iquest</code>

     <td> U+00BF

    <tr>
     <td> <code title="">isin</code>

     <td> U+2208

    <tr>
     <td> <code title="">iuml</code>

     <td> U+00EF

    <tr>
     <td> <code title="">kappa</code>

     <td> U+03BA

    <tr>
     <td> <code title="">lArr</code>

     <td> U+21D0

    <tr>
     <td> <code title="">lambda</code>

     <td> U+03BB

    <tr>
     <td> <code title="">lang</code>

     <td> U+2329

    <tr>
     <td> <code title="">laquo</code>

     <td> U+00AB

    <tr>
     <td> <code title="">larr</code>

     <td> U+2190

    <tr>
     <td> <code title="">lceil</code>

     <td> U+2308

    <tr>
     <td> <code title="">ldquo</code>

     <td> U+201C

    <tr>
     <td> <code title="">le</code>

     <td> U+2264

    <tr>
     <td> <code title="">lfloor</code>

     <td> U+230A

    <tr>
     <td> <code title="">lowast</code>

     <td> U+2217

    <tr>
     <td> <code title="">loz</code>

     <td> U+25CA

    <tr>
     <td> <code title="">lrm</code>

     <td> U+200E

    <tr>
     <td> <code title="">lsaquo</code>

     <td> U+2039

    <tr>
     <td> <code title="">lsquo</code>

     <td> U+2018

    <tr>
     <td> <code title="">lt</code>

     <td> U+003C

    <tr>
     <td> <code title="">LT</code>

     <td> U+003C

    <tr>
     <td> <code title="">macr</code>

     <td> U+00AF

    <tr>
     <td> <code title="">mdash</code>

     <td> U+2014

    <tr>
     <td> <code title="">micro</code>

     <td> U+00B5

    <tr>
     <td> <code title="">middot</code>

     <td> U+00B7

    <tr>
     <td> <code title="">minus</code>

     <td> U+2212

    <tr>
     <td> <code title="">mu</code>

     <td> U+03BC

    <tr>
     <td> <code title="">nabla</code>

     <td> U+2207

    <tr>
     <td> <code title="">nbsp</code>

     <td> U+00A0

    <tr>
     <td> <code title="">ndash</code>

     <td> U+2013

    <tr>
     <td> <code title="">ne</code>

     <td> U+2260

    <tr>
     <td> <code title="">ni</code>

     <td> U+220B

    <tr>
     <td> <code title="">not</code>

     <td> U+00AC

    <tr>
     <td> <code title="">notin</code>

     <td> U+2209

    <tr>
     <td> <code title="">nsub</code>

     <td> U+2284

    <tr>
     <td> <code title="">ntilde</code>

     <td> U+00F1

    <tr>
     <td> <code title="">nu</code>

     <td> U+03BD

    <tr>
     <td> <code title="">oacute</code>

     <td> U+00F3

    <tr>
     <td> <code title="">ocirc</code>

     <td> U+00F4

    <tr>
     <td> <code title="">oelig</code>

     <td> U+0153

    <tr>
     <td> <code title="">ograve</code>

     <td> U+00F2

    <tr>
     <td> <code title="">oline</code>

     <td> U+203E

    <tr>
     <td> <code title="">omega</code>

     <td> U+03C9

    <tr>
     <td> <code title="">omicron</code>

     <td> U+03BF

    <tr>
     <td> <code title="">oplus</code>

     <td> U+2295

    <tr>
     <td> <code title="">or</code>

     <td> U+2228

    <tr>
     <td> <code title="">ordf</code>

     <td> U+00AA

    <tr>
     <td> <code title="">ordm</code>

     <td> U+00BA

    <tr>
     <td> <code title="">oslash</code>

     <td> U+00F8

    <tr>
     <td> <code title="">otilde</code>

     <td> U+00F5

    <tr>
     <td> <code title="">otimes</code>

     <td> U+2297

    <tr>
     <td> <code title="">ouml</code>

     <td> U+00F6

    <tr>
     <td> <code title="">para</code>

     <td> U+00B6

    <tr>
     <td> <code title="">part</code>

     <td> U+2202

    <tr>
     <td> <code title="">permil</code>

     <td> U+2030

    <tr>
     <td> <code title="">perp</code>

     <td> U+22A5

    <tr>
     <td> <code title="">phi</code>

     <td> U+03C6

    <tr>
     <td> <code title="">pi</code>

     <td> U+03C0

    <tr>
     <td> <code title="">piv</code>

     <td> U+03D6

    <tr>
     <td> <code title="">plusmn</code>

     <td> U+00B1

    <tr>
     <td> <code title="">pound</code>

     <td> U+00A3

    <tr>
     <td> <code title="">prime</code>

     <td> U+2032

    <tr>
     <td> <code title="">prod</code>

     <td> U+220F

    <tr>
     <td> <code title="">prop</code>

     <td> U+221D

    <tr>
     <td> <code title="">psi</code>

     <td> U+03C8

    <tr>
     <td> <code title="">quot</code>

     <td> U+0022

    <tr>
     <td> <code title="">QUOT</code>

     <td> U+0022

    <tr>
     <td> <code title="">rArr</code>

     <td> U+21D2

    <tr>
     <td> <code title="">radic</code>

     <td> U+221A

    <tr>
     <td> <code title="">rang</code>

     <td> U+232A

    <tr>
     <td> <code title="">raquo</code>

     <td> U+00BB

    <tr>
     <td> <code title="">rarr</code>

     <td> U+2192

    <tr>
     <td> <code title="">rceil</code>

     <td> U+2309

    <tr>
     <td> <code title="">rdquo</code>

     <td> U+201D

    <tr>
     <td> <code title="">real</code>

     <td> U+211C

    <tr>
     <td> <code title="">reg</code>

     <td> U+00AE

    <tr>
     <td> <code title="">REG</code>

     <td> U+00AE

    <tr>
     <td> <code title="">rfloor</code>

     <td> U+230B

    <tr>
     <td> <code title="">rho</code>

     <td> U+03C1

    <tr>
     <td> <code title="">rlm</code>

     <td> U+200F

    <tr>
     <td> <code title="">rsaquo</code>

     <td> U+203A

    <tr>
     <td> <code title="">rsquo</code>

     <td> U+2019

    <tr>
     <td> <code title="">sbquo</code>

     <td> U+201A

    <tr>
     <td> <code title="">scaron</code>

     <td> U+0161

    <tr>
     <td> <code title="">sdot</code>

     <td> U+22C5

    <tr>
     <td> <code title="">sect</code>

     <td> U+00A7

    <tr>
     <td> <code title="">shy</code>

     <td> U+00AD

    <tr>
     <td> <code title="">sigma</code>

     <td> U+03C3

    <tr>
     <td> <code title="">sigmaf</code>

     <td> U+03C2

    <tr>
     <td> <code title="">sim</code>

     <td> U+223C

    <tr>
     <td> <code title="">spades</code>

     <td> U+2660

    <tr>
     <td> <code title="">sub</code>

     <td> U+2282

    <tr>
     <td> <code title="">sube</code>

     <td> U+2286

    <tr>
     <td> <code title="">sum</code>

     <td> U+2211

    <tr>
     <td> <code title="">sup</code>

     <td> U+2283

    <tr>
     <td> <code title="">sup1</code>

     <td> U+00B9

    <tr>
     <td> <code title="">sup2</code>

     <td> U+00B2

    <tr>
     <td> <code title="">sup3</code>

     <td> U+00B3

    <tr>
     <td> <code title="">supe</code>

     <td> U+2287

    <tr>
     <td> <code title="">szlig</code>

     <td> U+00DF

    <tr>
     <td> <code title="">tau</code>

     <td> U+03C4

    <tr>
     <td> <code title="">there4</code>

     <td> U+2234

    <tr>
     <td> <code title="">theta</code>

     <td> U+03B8

    <tr>
     <td> <code title="">thetasym</code>

     <td> U+03D1

    <tr>
     <td> <code title="">thinsp</code>

     <td> U+2009

    <tr>
     <td> <code title="">thorn</code>

     <td> U+00FE

    <tr>
     <td> <code title="">tilde</code>

     <td> U+02DC

    <tr>
     <td> <code title="">times</code>

     <td> U+00D7

    <tr>
     <td> <code title="">trade</code>

     <td> U+2122

    <tr>
     <td> <code title="">TRADE</code>

     <td> U+2122

    <tr>
     <td> <code title="">uArr</code>

     <td> U+21D1

    <tr>
     <td> <code title="">uacute</code>

     <td> U+00FA

    <tr>
     <td> <code title="">uarr</code>

     <td> U+2191

    <tr>
     <td> <code title="">ucirc</code>

     <td> U+00FB

    <tr>
     <td> <code title="">ugrave</code>

     <td> U+00F9

    <tr>
     <td> <code title="">uml</code>

     <td> U+00A8

    <tr>
     <td> <code title="">upsih</code>

     <td> U+03D2

    <tr>
     <td> <code title="">upsilon</code>

     <td> U+03C5

    <tr>
     <td> <code title="">uuml</code>

     <td> U+00FC

    <tr>
     <td> <code title="">weierp</code>

     <td> U+2118

    <tr>
     <td> <code title="">xi</code>

     <td> U+03BE

    <tr>
     <td> <code title="">yacute</code>

     <td> U+00FD

    <tr>
     <td> <code title="">yen</code>

     <td> U+00A5

    <tr>
     <td> <code title="">yuml</code>

     <td> U+00FF

    <tr>
     <td> <code title="">zeta</code>

     <td> U+03B6

    <tr>
     <td> <code title="">zwj</code>

     <td> U+200D

    <tr>
     <td> <code title="">zwnj</code>

     <td> U+200C
  </table>

  <h2 id=wysiwyg><span class=secno>9. </span>WYSIWYG editors</h2>

  <p><dfn id=wysiwyg1>WYSIWYG editors</dfn> are authoring tools with a
   predominantly presentation-driven user interface.

  <h3 id=presentational><span class=secno>9.1. </span>Presentational markup</h3>

  <h4 id=wysiwyg0><span class=secno>9.1.1. </span><dfn id=wysiwyg2>WYSIWYG
   signature</dfn></h4>

  <p>WYSIWYG editors must include a <code><a href="#meta0">meta</a></code>
   element in the <code><a href="#head">head</a></code> element whose <code
   title=attr-meta-name><a href="#name">name</a></code> attribute has the
   value <code title=meta-generator><a href="#generator">generator</a></code>
   and whose <code title=attr-meta-content><a
   href="#content0">content</a></code> attribute's value ends with the string
   "<code title="">(WYSIWYG editor)</code>". Non-WYSIWYG authoring tools must
   not include this string in their generator string.

  <h4 id=the-font><span class=secno>9.1.2. </span>The <dfn
   id=font><code>font</code></dfn> element</h4>

  <p><a href="#transparent0">Transparent</a> <a href="#block-level0"
   title="block-level elements">block-level element</a>, and <a
   href="#transparent0">transparent</a> <a href="#strictly">strictly
   inline-level content</a>.

  <dl class=element>
   <dt>Contexts in which this element may be used:

   <dd>Where <span>block-level content</span> is allowed.

   <dd>Where <a href="#strictly">strictly inline-level content</a> is
    allowed.

   <dt>Content model:

   <dd><a href="#transparent0">Transparent</a>.

   <dt>Element-specific attributes:</dt>
   <!--
   <dd><code title="attr-font-color">color</code></dd>
   <dd><code title="attr-font-face">face</code></dd>
   <dd><code title="attr-font-size">size</code></dd>-->

   <dd><code title=attr-font-style><a href="#style0">style</a></code>

   <dt>DOM interface:

   <dd>
    <pre
     class=idl>interface <dfn id=htmlfontelement>HTMLFontElement</dfn> : <a href="#htmlelement">HTMLElement</a> {<!--
           attribute DOMString <span title="dom-font-color">color</span>;
           attribute DOMString <span title="dom-font-face">face</span>;
           attribute DOMString <span title="dom-font-size">size</span>;-->
  readonly attribute CSSStyleDeclaration <a href="#style1" title=dom-font-style>style</a>;
};</pre>
  </dl>

  <p>The <code><a href="#font">font</a></code> element doesn't represent
   anything. It must not be used except by <a href="#wysiwyg1">WYSIWYG
   editors</a>, which may use it to achieve presentational affects. Even
   WYSIWYG editors, however, should make every effort to use appropriate
   semantic markup and avoid the use of media-specific presentational markup.

  <p>Conformance checkers must consider this element to be non-conforming if
   it is used on a page lacking the <a href="#wysiwyg2">WYSIWYG
   signature</a>.

  <p>A <code><a href="#font">font</a></code> element can only contain content
   that would still be conformant if all elements with <a
   href="#transparent0">transparent</a> content models were replaced by their
   contents.

  <div class=example>
   <p>The following would be syntactically legal (as the output from a
    WYSIWYG editor, though not anywhere else):</p>

   <pre>&lt;!DOCTYPE HTML>
&lt;html>
 &lt;head>
  &lt;title>&lt;/title>
  &lt;meta name="generator" content="Sample Editor 1.0 <em>(WYSIWYG editor)</em>">
 &lt;/head>
 &lt;body>
  &lt;font style="display: block; border: solid">
   &lt;h1>Hello.&lt;/h1>
  &lt;/font>
  &lt;p>
   &lt;font style="color: orange; background: white">How&lt;/font>
   &lt;font style="color: yellow; background: white">do&lt;/font>
   &lt;font style="color: green; background: white"><em>&lt;em></em>you<em>&lt;/em></em>&lt;/font>
   &lt;font style="color: blue; background: white">do?&lt;/font>
  &lt;/p>
 &lt;/body>
&lt;/html></pre>

   <p>The first <code><a href="#font">font</a></code> element is conformant
    because <code><a href="#h1">h1</a></code> and <code><a
    href="#p">p</a></code> elements are both allowed in <code><a
    href="#body0">body</a></code> elements. the next four are allowed because
    text and <code><a href="#em">em</a></code> elements are allowed in
    <code><a href="#p">p</a></code> elements.</p>
  </div>

  <p>The <dfn id=style0 title=attr-font-style><code>style</code></dfn>
   attribute, if specified, must contain only a list of zero or more
   semicolon-separated (;) CSS declarations. <a href="#refsCSS21">[CSS21]</a></p>
  <!-- XXX deal with each of the use cases in this:
  http://lists.w3.org/Archives/Public/www-html/2003Jan/0277.html -->

  <p>The declarations specified must be parsed and treated as the body of a
   declaration block whose selector matches just that <code><a
   href="#font">font</a></code> element. For the purposes of the CSS cascade,
   the attribute must be considered to be a 'style' attribute at the author
   level.

  <p>The <dfn id=style1 title=dom-font-style><code>style</code></dfn> DOM
   attribute must return a <code>CSSStyleDeclaration</code> whose value
   represents the declarations specified in the attribute, if present.
   Mutating the <code>CSSStyleDeclaration</code> object must create a <code
   title=attr-font-style><a href="#style0">style</a></code> attribute on the
   element (if there isn't one already) and then change its value to be a
   value representing the serialised form of the
   <code>CSSStyleDeclaration</code> object. <a href="#refsCSSOM">[CSSOM]</a>

  <h2 id=rendering><span class=secno>10. </span>Rendering</h2>

  <p class=big-issue>This section will probably include details on how to
   render DATAGRID (including <span id=datagridPseudos>its
   pseudo-elements</span>), drag-and-drop, etc, in a visual medium, in
   concert with CSS. Terms that need to be defined include: <dfn
   id=sizing>sizing of embedded content</dfn>

  <p>CSS UAs in visual media must, when scrolling a page to a fragment
   identifier, align the top of the viewport with the target element's top
   border edge.</p>
  <!-- XXX horiz pos given bidi, and not
  scrolling when not required to? -->
  <!-- Elements that have been dropped: ACRONYM APPLET B BASEFONT BLINK
BIG CENTER DIR DIV FONT FRAME FRAMESET I ISINDEX MARQUEE NOEMBED
NOFRAMES S SPACER STRIKE TT U -->
  <!-- XXX bits and pieces that were removed from the semantic parts:

  <p>In CSS-aware user agents, the default presentation of this
  element should be achieved by including the following rules, or
  their equivalent, in the UA's user agent style sheet:</p>

  <pre>@namespace xh url(http://www.w3.org/1999/xhtml);
xh|section { display: block; margin: 1em 0; }</pre>

  <h4>Section headers</h4>

  <p>For <code>h1</code> elements, CSS-aware visual user agents should
  derive the size of the header from the level of <code>section</code>
  nesting. This effect should be achieved by including the following
  rules, or their equivalent, in the UA's user agent style sheet:</p>

  <pre>@namespace xh url(http://www.w3.org/1999/xhtml);
xh|section xh|h1 { /* same styles as h2 */ }
xh|section xh|section xh|h1 { /* same styles as h4 */ }
xh|section xh|section xh|section xh|h1 { /* same styles as h4 */ }
xh|section xh|section xh|section xh|section xh|h1 { /* same styles as h5 */ }
xh|section xh|section xh|section xh|section xh|section xh|h1 { /* same styles as h6 */ }</pre>

  <p>Authors should use <code>h1</code> elements to denote headers in
  sections. Authors may instead use <code>h2</code> ...
  <code>h6</code> elements, for backwards compatibility with user
  agents that do not support <code>section</code> elements.</p>

-->

  <p class=big-issue> must define letting the user <dfn id=obtain>obtain a
   physical form</dfn> of a document (printing) and what this means for the
   UA

  <h3 id=rendering0><span class=secno>10.1. </span>Rendering and the DOM</h3>

  <p class=big-issue>This section is wrong. mediaMode will end up on Window,
   I think. All views implement Window.

  <p>Any object implement the <code>AbstractView</code> interface must also
   implement the <code><a
   href="#mediamodeabstractview">MediaModeAbstractView</a></code> interface.

  <pre
   class=idl>interface <dfn id=mediamodeabstractview>MediaModeAbstractView</dfn> {
  readonly attribute DOMString <a href="#mediamode">mediaMode</a>;
};</pre>

  <p>The <dfn id=mediamode><code>mediaMode</code></dfn> attribute on objects
   implementing the <code><a
   href="#mediamodeabstractview">MediaModeAbstractView</a></code> interface
   must return the string that represents the canvas' current rendering mode
   (<code>screen</code>, <code>print</code>, etc). This is a lowercase
   string, as <a
   href="http://www.w3.org/TR/CSS21/media.html#media-types">defined by the
   CSS specification</a>. <a href="#refsCSS21">[CSS21]</a>

  <p>Some user agents may support multiple media, in which case there will
   exist multiple objects implementing the <code>AbstractView</code>
   interface. Only the default view implements the <code><a
   href="#window">Window</a></code> interface. The other views can be reached
   using the <code><a href="#view">view</a></code> attribute of the
   <code>UIEvent</code> inteface, during event propagation. There is no way
   currently to enumerate all the views.</p>
  <!-- XXX examples! -->

  <h2 id=no><span class=secno>11. </span>Things that you can't do with this
   specification because they are better handled using other technologies
   that are further described herein</h2>

  <p><em>This section is non-normative.</em>

  <p>There are certain features that are not handled by this specification
   because a client side markup language is not the right level for them, or
   because the features exist in other languages that can be integrated into
   this one. This section covers some of the more common requests.

  <h3 id=localisation><span class=secno>11.1. </span>Localisation</h3>

  <p>If you wish to create localised versions of an HTML application, the
   best solution is to preprocess the files on the server, and then use HTTP
   content negotation to serve the appropriate language.</p>
  <!-- <p>XXX example here</p> -->

  <h3 id=declarative><span class=secno>11.2. </span>Declarative 2D vector
   graphics and animation</h3>

  <p>Embedding vector graphics into XHTML documents is the domain of SVG.</p>
  <!-- <p>XXX example here</p> -->

  <h3 id=declarative0><span class=secno>11.3. </span>Declarative 3D scenes</h3>

  <p>Embedding 3D imagery into XHTML documents is the domain of X3D, or
   technologies based on X3D that are namespace-aware.</p>
  <!-- <p>XXX example here</p> -->

  <h3 id=timers><span class=secno>11.4. </span>Timers</h3>

  <p>This section is expected to be moved to the Window Object specification
   in due course.

  <pre class=idl>
interface <dfn id=windowtimers>WindowTimers</dfn> {
  // timers
  long <a href="#settimeout">setTimeout</a>(in <a href="#timeouthandler">TimeoutHandler</a> handler, in long timeout);
  long <a href="#settimeout">setTimeout</a>(in <a href="#timeouthandler">TimeoutHandler</a> handler, in long timeout, <var title="">arguments...</var>);
  long <a href="#settimeout">setTimeout</a>(in DOMString code, in long timeout);
  long <a href="#settimeout">setTimeout</a>(in DOMString code, in long timeout, in DOMString language);
  void <a href="#cleartimeout">clearTimeout</a>(in long handle);
  long <a href="#setinterval...">setInterval</a>(in <a href="#timeouthandler">TimeoutHandler</a> handler, in long timeout);
  long <a href="#setinterval...">setInterval</a>(in <a href="#timeouthandler">TimeoutHandler</a> handler, in long timeout, <var title="">arguments...</var>);
  long <a href="#setinterval...">setInterval</a>(in DOMString code, in long timeout);
  long <a href="#setinterval...">setInterval</a>(in DOMString code, in long timeout, in DOMString language);
  void <a href="#clearinterval">clearInterval</a>(in long handle);
};

interface <dfn id=timeouthandler>TimeoutHandler</dfn> {
  void handleEvent(<var title="">arguments...</var>);
};
</pre>

  <p>The <code><a href="#windowtimers">WindowTimers</a></code> interface must
   be obtainable from any <code><a href="#window">Window</a></code> object
   using binding-specific casting methods.

  <p>The <code><a href="#settimeout">setTimeout</a></code> and <code><a
   href="#setinterval...">setInterval</a></code> methods allow authors to
   schedule timer-based events.

  <p>The <dfn id=settimeout title=setTimeout><code>setTimeout(<var
   title="">handler</var>, <var title="">timeout</var>[, <var
   title="">arguments...</var>])</code></dfn> method takes a reference to a
   <code><a href="#timeouthandler">TimeoutHandler</a></code> object and a
   length of time in milliseconds. It must return a handle to the timeout
   created, and then asynchronously wait <var title="">timeout</var>
   milliseconds and then invoke <code>handleEvent()</code> on the <var
   title="">handler</var> object. If any <var title="">arguments...</var>
   were provided, they must be passed to the <var title="">handler</var> as
   arguments to the <code>handleEvent()</code> function.

  <p>In the ECMAScript DOM binding, the ECMAScript native
   <code>Function</code> type must implement the <code><a
   href="#timeouthandler">TimeoutHandler</a></code> interface such that
   invoking the <code>handleEvent()</code> method of that interface on the
   object from another language binding invokes the function itself, with the
   arguments passed to <code>handleEvent()</code> as the arguments passed to
   the function. In the ECMAScript DOM binding itself, however, the
   <code>handleEvent()</code> method of the interface is not directly
   accessible on <code>Function</code> objects. Such functions must be called
   in the scope of the <a href="#browsing0">browsing context</a> in which
   they were created.

  <p>Alternatively, <dfn id=settimeout0 title=""><code>setTimeout(<var
   title="">code</var>, <var title="">timeout</var>[, <var
   title="">language</var>])</code></dfn> may be used. This variant takes a
   string instead of a <code><a
   href="#timeouthandler">TimeoutHandler</a></code> object. That string must
   be parsed using the specified <var title="">language</var> (defaulting to
   ECMAScript if the third argument is omitted) and executed in the scope of
   the <a href="#browsing0">browsing context</a> associated with the <code><a
   href="#window">Window</a></code> object on which the <code
   title=setTimeout><a href="#settimeout">setTimeout()</a></code> method was
   invoked.

  <p class=big-issue>Need to define <var title="">language</var> values.

  <p>The <dfn id=setinterval...><code>setInterval(...)</code></dfn> variants
   must work in the same way as the <code><a
   href="#settimeout">setTimeout</a></code> variants except that the <var
   title="">handler</var> or <code><a href="#code">code</a></code> must be
   invoked again every <var title="">timeout</var> milliseconds, not just the
   once.

  <p>The <dfn id=cleartimeout><code>clearTimeout()</code></dfn> and <dfn
   id=clearinterval><code>clearInterval()</code></dfn> methods take one
   integer (the value returned by <code><a
   href="#settimeout">setTimeout</a></code> and <code><a
   href="#setinterval...">setInterval</a></code> respectively) and must
   cancel the specified timeout. When called with a value that does not
   correspond to an active timeout or interval, the methods must return
   without doing anything.

  <p>Timeouts must never fire while another script is executing. (Thus the
   HTML scripting model is strictly single-threaded and not reentrant.)

  <h3 id=events2><span class=secno>11.5. </span>Events</h3>

  <p id=js-function-listener>In the ECMAScript DOM binding, the ECMAScript
   native <code>Function</code> type must implement the
   <code>EventListener</code> interface such that invoking the
   <code>handleEvent()</code> method of that interface on the object from
   another language binding invokes the function itself, with the
   <code>event</code> argument as its only argument. In the ECMAScript
   binding itself, however, the <code>handleEvent()</code> method of the
   interface is not directly accessible on <code>Function</code> objects.
   Such functions, when invoked, must be called in the scope of the <a
   href="#browsing0">browsing context</a> that they were created in.

  <h2 class=no-num id=references>References</h2>

  <p class=big-issue>This section will be written in a future
   draft.<!--XXX-->

  <h2 class=no-num id=acknowledgements>Acknowledgements</h2>

  <p>Thanks to Aankhen, Aaron Leventhal, Adrian Sutton, Alexey Feldgendler,
   Andrew Gove, Anne van Kesteren, Anthony Hickson, Asbj&oslash;rn Ulsberg,
   Ben Godfrey, Ben Meadowcroft, Benjamin Hawkes-Lewis, Bert Bos, Bjoern
   Hoehrmann, Boris Zbarsky, Brad Fults, Brad Neuberg, Brendan Eich, Brett
   Wilson, Carlos Perell&oacute; Mar&iacute;n, Chao Cai, Channy Yun, Charl
   van Niekerk<!--status.whatwg.org maintainer-->, Charles Iliya Krempeaux,
   Charles McCathieNevile, Christian Biesinger, Christian Johansen, Chriswa,
   Daniel Peng, Daniel Sp&aring;ng, Darin Alder, Darin Fisher, Dave
   Townsend<!-- Mossop on moz irc -->, David Baron, David Flanagan, David
   H&aring;s&auml;ther, David Hyatt, Derek Featherstone, Dimitri Glazkov,
   dolphinling, Doron Rosenberg, Eira Monstad, Elliotte Harold, Erik
   Arvidsson, fantasai, Franck 'Shift' Qu&eacute;lain, Geoffrey Sneddon,
   H&aring;kon Wium Lie, Henri Sivonen, Henrik Lied, Ignacio Javier, J. King,
   James Graham, James M Snell, James Perrett, Jan-Klaas Kollhof, Jasper
   Bryant-Greene, Jeff Cutsinger, Jens Bannmann, Joel Spolsky, John Harding,
   Johnny Stenback, Jon Perlow, Jonathan Worent, Jorgen Horstink, Josh
   Levenberg, Joshua Randall, Jukka K. Korpela, Kai Hendry, <!-- Keryx
  Web, = Lars Gunther -->
   Kornel Lesinski, &#x9ed2;&#x6fa4;&#x525b;&#x5fd7; (KUROSAWA Takeshi),
   Kristof Zelechovski, Lachlan Hunt, Larry Page, Lars Gunther, Laurens
   Holst, Lenny Domnitser, L&eacute;onard Bouchet, Leons Petrazickis,
   Logan<!-- on moz irc -->, Maciej Stachowiak, Malcolm Rowe, Mark
   Nottingham, Mark Schenk, Martijn Wargers, Martin Atkins, Martin Honnen,
   Mathieu Henri, Matthew Mastracci, Matthew Raymond, Matthew Thomas, Mattias
   Waldau, Max Romantschuk, Michael 'Ratt' Iannarelli, Michael A. Nachbaur,
   Michael A. Puls II<!--Shadow2531-->, Michael Gratton, Michael Powers,
   Michel Fortin, Mihai &#x015E;ucan<!-- from
  ROBO Design -->, Mike
   Dierken<!-- S. Mike Dierken -->, Mike Dixon, Mike Schinkel, Mike Shaver,
   Mikko Rantalainen, Neil Deakin, Olav Junker Kj&aelig;r, Philip Taylor,
   Rajas Moonka, Rimantas Liubertas, Robert O'Callahan, Robert Sayre, Roman
   Ivanov, S. Mike Dierken, Sam Ruby, Sean Knapp, Shaun Inman, Simon Pieters,
   Stefan Haustein, Stephen Ma, Steve Runyon, Steven Garrity, Stewart Brodie,
   Stuart Parmenter, Tantek &Ccedil;elik, Thomas Broyer, Thomas O'Connor, Tim
   Altman, Vladimir Vuki&#x0107;evi&#x0107;, Wakaba, William Swanson, and
   everyone on the WHATWG mailing list for their useful and substantial
   comments.

  <p>Special thanks to Richard Williamson for creating the first
   implementation of <code><a href="#canvas">canvas</a></code> in Safari,
   from which the canvas feature was designed.

  <p>Special thanks also to the Microsoft employees who first implemented the
   event-based drag-and-drop mechanism, <code title=attr-contenteditable><a
   href="#contenteditable0">contenteditable</a></code>, and other features
   first widely deployed by the Windows Internet Explorer browser.

  <p>Special thanks and $10,000 to David Hyatt who came up with a broken
   implementation of the <a href="#adoptionAgency">adoption agency
   algorithm</a> that the editor had to reverse engineer and fix before using
   it in the parsing section.

  <p>Thanks also the Microsoft blogging community for some ideas, to the
   attendees of the W3C Workshop on Web Applications and Compound Documents
   for inspiration, and to the #mrt crew, the #mrt.no crew, and the cabal for
   their ideas and support.</p>
  <!-- Hopefully Kam won't notice he's covered by these
  acknowledgements three times! -->
  <!--
 !  menus

<hyatt> the ability to get the current focused window in a window hierarchy

wizards
tabbed interface

Application object? http://longhorn.msdn.microsoft.com/lhsdk/ref/ns/msavalon.windows/c/application/application.aspx

<input type="text" menu="foo" icon="g.png"/> <menu id="foo"> <menuitem icon="g.png" onclick="engine('yahoo')">Yahoo</menuitem> ... </menu>

> One more aspect I want you think about - for "user interface systems" in
> general: The windowing system.
>   Different kinds of windows ("document", "browser (file-system/network or
> otherwise)", "palette", "application modal dialog", "system modal dialog"),
> the rules for layering them (appropriately flexible to allow different
> implementations, e.g. MacOS vs. X-Windows), and simplifications for handheld
> devices (which are sometimes single window devices anyway, but sometimes
> they are one "normal" window plus sometimes one "dialog" window on top.

window.open for dialogs


Thus, they lack things like proper windows, tree 
widgets, menu bars, rich text areas and so forth. This is what I would 
like XUL to solve. - Paul Prescod




Olav:
> <product> to indicate something you can buy, like a cd on amazon
> or a biker jacket at harleydavidson.com


Drop downs often have a title for when there is no selection.

http://www.w3.org/mid/BAY1-F150PNOkJvX41K000418e1@hotmail.com

http://crew.tweakers.net/crisp/newlayout/index.html
http://crew.tweakers.net/crisp/newlayout/list_topics.html
http://crew.tweakers.net/crisp/newlayout/list_messages.html
http://crew.tweakers.net/crisp/newlayout/list_messages_mod.html

http://mail.mozilla.org/private/gui-toolkit/2004-April/000041.html

> > > A standard for rich edit widgets would also be of interest to me.
> >
> > As in WYSIWIG editing? Of the bold/italic/underline/larger/smaller kind?
> > 
> > Or do you mean as in the bare bones to be able to build an editor on top
> > of? As in something that basically just gives you a cursor and the ability
> > to tell where the selection is and some way to hook into the Undo
> > functionality?
> 
> I have use cases for both...I have a more desperate business need for
> the latter (and have build apps using the gross APIs out there today)
> but there are a lot of circumstances where an editor that already has
> all standard HTML editing behaviour would be fine.
>
- Paul Prescod

 * a way of selecting rows, so that you can declaratively have buttons
   outside the template that move a "selected row" around. => web apps


Calendar with list of days that have events (think: blog calendars)

Find object at (x,y)
Find mouse position

Styling scrollbars:

   ::scrollbars { ... }


table of contents?


http://www.gadgetopia.com/2004/05/04/FileIconTag.html


on going back
on going forward
on came from back
on came from forward
better state serialisation for going back/forward


some sort of markup to tell google _not_ to index a particular part of the site

drop down menu with URIs to replace the silly <select> hacks.

http://www.cs.tut.fi/~jkorpela/html/em.html

<htmlarea>, <xmlarea>...

> 3) Extensible syntax highlighting (coloring). I am aware that a ton of
> code editors don't even do this well. The ability to load a syntax
> definition file and have it color a block of code would do wonders for
> making the web a more friendly place to script.
 - Ryan Johnson

toolbars, status bars. - Didier PH Martin

   * methods/properties for scrolling managing, especially in
   TextArea, such as .scrollTop and .scrollHeight in Mozilla and -


Robert Bateman:

   I've looked thru as many of the examples from around the web as I can find and
   don't see an obvious way to do date calculations.

   What I'm trying to do is populate an xsd:date field with now() plus 5 days as
   it's default value.  The field in question is a proposed "due date" for a
   work order.

   I've seen that I can get a "difference" between two dates, but no
   calculations.


Wladimir Palant pointed out problems with chunking with server-sent-events



> 2.  Some method of integration to allow Web apps to respond
>      to the browser's Cut, Copy, Paste, and Select All menu
>      items and keyboard equivalents. These work automatically
>      for text fields in any Web application; it would be
>      great if apps could make them work for stocks, address
>      book cards, message attachments, transactions, photos,
>      and so on too.
>
>      I'd add Undo and Redo to that list, but unfortunately
>      IE6 doesn't have Undo and Redo menu items.
 - mpt



>> maybe except for the server sent events and the clipboard
>> api (but even in those cases it might be possible).
>
> Clipboard API I don't really want to see, given the problems IE's
> implementation of such brought up. A better standardised drag-and-drop
> interface would be great though, as doing it with mouse events and IE's
> proprietary events is annoying-to-impossible to get right all the time.
>
> I really like the idea of server-side events, though I would prefer to
> have them set up by a scripting call rather than an HTML element.
 - Andrew Clover


    <html application="application">

...would, instead of showing the Web page itself, the first time, show
(inline in the browser):

  :::: Security Warning :::::::::::::::::::::::::::::::::::::
  ::                                                       ::
  ::  The Web page at this domain:                         ::
  ::                                                       ':
  ::     paypcl.com                                        
  ::                                                       
  ::  ...wishes to launch an application in a separate     
  ::  window. Do you trust this domain?                    
  ::                                                       
  ::  [x] Remember this decision.                          
  ::                                                       
  ::      (( Trust paypcl.com ))  ( Display as Web page )  
  ::                                                      
  :::::.
- (spurred on by Jose Dinuncio)


  :::: Security Warning :::::::::::::::::::::::::::::::::::::
  ::                                                       ::
  ::  This Web page wishes to launch an application in a   ::
  ::  separate window. Do you trust this domain?           ::
  ::                                                       ::
  ::     paypcl.com                                         '
  ::                                                       
  ::             ( Trust this site for now )
  ::
  ::              ( Always trust this site )
  ::
  ::              (( Display as Web page ))
  ::                                                      
  :::::.


breadcrumb navigation markup
other markup:
   http://www.stuffandnonsense.co.uk/archives/whats_in_a_name_pt2.html


common icons: http://www.intersmash.com/300images/


http://www.gadgetopia.com/2004/06/18/DoYouWantToSaveYourChanges.html#Comments

http://www.mojavelinux.com/cooker/demos/domTT/index.html

http://www.mozilla.org/projects/ui/accessibility/dynamic-accessibility.html

http://blog.colorstudy.com/ianb/weblog/2004/06/23.html
http://daringfireball.net/2004/06/location_field

listview/gridview API
http://www.activewidgets.com/grid/


> I would rather have it that changing the dom attribute 'value' or typing
> in the textarea, would also change the contents of the textnode in the
> textarea.
>
> In that way the dom level 2 traversal and range specification would not
> be useless for textarea's.
> 
> The same goes for input text controls and probably also for other form
> controls.
 - martijnw



1. point to an xml instance and cause the page to be filled in
2. serialise the site to a version of that xml instance

<menu>
 <li state="bar"/>
</menu>
<button state="bar"/>
<state id="bar" label="" disabled="" value=""/>

<input state="foo"/>
<input state="foo"/>
<input state="foo 2"/>
<input state="foo 2"/>
<state id="foo" model="x" ref="cat:orderLine[$v1]/cat:foo"/>

<instance src=""/>

<instance id="x">

<Order xmlns="urn:oasis:names:tc:ubl:Order:1.0:0.70" xmlns:cat="urn:oasis:names:tc:ubl:CommonAggregateTypes:1.0:0.70">
  <cat:ID/>
  <cat:IssueDate/>
  <cat:LineExtensionTotalAmount currencyID="USD"/>
  <cat:BuyerParty>
    <cat:ID/>
    <cat:PartyName>
      <cat:Name/>
    </cat:PartyName>
    <cat:Address>
      <cat:ID/>
      <cat:Street/>
      <cat:CityName/>
      <cat:PostalZone/>
      <cat:CountrySub-Entity/>
    </cat:Address>
    <cat:BuyerContact>
      <cat:ID/>
      <cat:Name/>
    </cat:BuyerContact>
  </cat:BuyerParty>
  <cat:SellerParty>
    <cat:ID/>
    <cat:PartyName>
      <cat:Name/>
    </cat:PartyName>
    <cat:Address>
      <cat:ID/>
      <cat:Street/>
      <cat:CityName/>
      <cat:CountrySub-Entity/>
    </cat:Address>
  </cat:SellerParty>
  <cat:DeliveryTerms>
    <cat:ID/>
    <cat:SpecialTerms/>
  </cat:DeliveryTerms>
  <cat:OrderLine>
    <cat:BuyersID/>
    <cat:SellersID/>
    <cat:LineExtensionAmount currencyID=""/>
    <cat:Quantity unitCode="">1</cat:Quantity>
    <cat:Item>
      <cat:ID/>
      <cat:Description>Enter description here</cat:Description>
      <cat:SellersItemIdentification>
        <cat:ID>Enter part number here</cat:ID>
      </cat:SellersItemIdentification>
      <cat:BasePrice>
        <cat:PriceAmount currencyID="">0.00</cat:PriceAmount>
      </cat:BasePrice>
    </cat:Item>
  </cat:OrderLine>
</Order> 

</instance>




  <h2>Tree and List Widgets</h2>
   click item to go uri
   doube click to submit form with value
   sort list by any column
   specify column headers, column sort types
   specify data inline, or out of band
   data can be linear or a one way tree
   rows can have an icon associated with them
   rows can have overlays associated with them

 progress meter

    http://www.gazingus.org/html/menuDropdown.html



Disclosure triangles


I think UAs should automatically highlight the accesskey (or add it in    
brackets if it isn't already in the string). I am thinking of writing some
text - optional, of course, since this wouldn't apply to all UAs or all  
platforms - that specifies this.

I also think that there should be an accesskey value which is basically   
"auto", and which picks a non-clashing access key based on the element    
content.



| adding HTTP authentication capabilities to HTML allow sites to:
|   - remove a site's authentication state from the browser when
|     activated (i.e., a "log out" interface)
|   - add user data to a site's authentication state in the browser
|     (i.e., "log on" interfaces)
|   - display the user's current authentication state
| 
| There are a few good reasons to do this. Many sites use cookies to
| authenticate users, because HTTP authentication doesn't have any
| mechanism to allow logging out (a key requirement of financial
| institutions and other sensitive applications), and because the UI for
| HTTP authentication can't be controlled, and doesn't offer an
| "anyonymous" / "not logged in" view.
| 
| By accommodating HTTP authentication in Web forms, it will be possible
| to have styled, custom "log on" interfaces as part of pages, as well
| as "log out" facilities, while still retaining the benefits of HTTP
| authentication.
| 
| Specifically, HTTP authentication is more secure than cookies (when
| Digest auth is used), and is more amenable to automated processes
| (agents, spiders, etc.) as well as alternate browsing devices (screen
| readers, etc.).


http://jogin.com/weblog/archives/2004/07/19/hierarchy


Yeah, <header> and <footer> or similar elements are almost certainly going
to be defined at some point, along with <content> (for the main body of
the page), <entry> or <post> or <article> to refer to a unit of text
bigger than a section but smaller than a page, <aside> to mean a
side bar, <note> to mean a note... and so forth. Suggestions welcome.     
We'll probably keep it to a minimum though. The idea is just to relieve   
the most common pseudo-semantic uses of <div>.


http://lxr.mozilla.org/seamonkey/source/dom/public/idl/base/nsIDOMWindow.idl
scrollBy, etc
http://lxr.mozilla.org/seamonkey/source/dom/public/idl/base/nsIDOMWindowInternal.idl
DOM level 0


DH: I was arguing that you should be able to get the CSS info for
document fragments if you had an owner document with CSS in it.



So maybe:

   var library = new ZipFile("data.zip");
   library.onload = function() {
      var sound1 = library.getAudio("sound1.wav"); // returns an Audio object
      var image1 = library.getImage("image1.png"); // returns an HTMLImageElement
      var doc1 = library.getXMLDocument("doc1.xml"); // returns a Document
      var doc2 = library.getHTMLDocument("doc1.html"); // returns an HTMLDocument
   }

Also maybe supporting more than one file at a time:

   var library = new ResourceLoader("data.zip");
   library.add("moredata.zip");
   library.onload = function() { ... }
   library.onloading = function() {
      reportLoadProgress(library.progress); // 0.0 .. 1.0
   }

...although I'm not sure how we would then deal with filename clashes.

   var library = new AudioZip("sounds.zip");
   library.onload = function() {
      var sound1 = library["sound1.wav"];
      sound.play();
   }


If we define onbeforeunload, then we have to say that the JS
implementation of EventListener::handleEvent checks for that event,
treating the return value as the string to use for the unload warning
message if there is a return value, and calling preventDefault if
there isn't.


> > > Schematic editors, layout editors, interactive maps, data 
> > > visualization for network flows, etc.
> Searching the web for the above keywords should find you a lot more.
 - Denis Bohm



Jens Meiert:
- For non-native English speakers, it's sometimes difficult to understand
the difference between <cite /> and <quote />, since citations often seem to
be quoted, too (this is a presentational aspect, I know).
- Is it right that the <dfn /> element [1] /must/ be used only in the
context of the definition of the enclosed term (as the example suggests)?
(If so, wouldn't it be useful to add this note, too?)


http://secunia.com/advisories/9711/
In particular number 7. - Chris Hofmann


> [1] http://www.stopdesign.com/log/2004/08/25/microsoft-advances.html
> [2] http://www.stopdesign.com/articles/throwing_tables/


In other areas, however, the replacement is not a match in terms of functionality. Like it or not, but showModalDialog is a better way to provide feature-rich user feedback windows than window.confirm (which Firefox supports, even though there is NO PUBLIC STANDARD for it). With showModalDialog, I can pop a window offering "Yes," "No," or "Cancel" buttons that requires a response before proceeding. With window.confirm, I have to craft all my questions as something to which "OK" or "Cancel" makes sense, never mind asking for three, four, or five state responses.
- http://news.zdnet.com/2100-9588-5438955.html ( John Carroll )



> http://channel9.msdn.com/wiki/default.aspx/Channel9.InternetExplorerFeatureRequests
>    Alternate way of caching content
>    Avalon Integration
>    getData/setData improvement (clipboardData)
>    Input type=file improvements
>    HTML editing: Editing Tables
>    Input type=file improvements
>    .NET framework
>    
> http://channel9.msdn.com/wiki/default.aspx/Channel9.InternetExplorerOutrageous
>     Some decent controls
 - lachlan.hunt@lachy.id.au


http://lists.w3.org/Archives/Member/w3c-html-wg/2004JulSep/att-0135/role072704a.html


> I've encountered two situations where setting or retrieving the caret
> position would be useful.  The first is a situation where I'd like to
> apply an input mask to a text box.  For example, I'd like the ability to
> create a text box where the date delimiters (dashes or slashes) appear  
> automatically in a text box upon entering the field, and when the user  
> types in the field, it fills into the appropriate spaces in the input    
> box and sets the text selection to the next appropriate position, all    
> while allowing the user to reposition the cursor within the text box     
> with a keyboard or mouse without being able to edit or delete the
> delimiters (dashes or slashes).  This would be very similar to input
> mask features in certain native apps that I've used.
 - Greg Kilwein

> The second situation is an application that would like to highlight text  
> in a text box or textarea for the purposes of a spell check, thesaurus, 
> or search-and-replace operation.
 - Greg Kilwein




HTMLImageElement.click(x, y); (for Csaba Gabor)
or clickPoint, if click() can't be done in IE
can this be emulated in IE by posting a synthetic moue click event
with those X and Y coords?


<menulabel>, or rather menus in general, need an icon attribute and a
hide attribute, like the <command> element.


What about safe clipboard access.
As discussed before by others as well:
The user initiates a paste action as recognized by the UISystem the user is working in.
E.g pressing Ctrl-V or selecting paste from a context menu.
An event is fired and a Listener can now access the pasted data as part of the event object.
The same for cut and copy. The Listner can set data as part of the event object.
This is safe and will not allow any script to mess with the clipboard without the user specifically asking for it
by initiating a cut/copy/paste action.
 -  Jan-Klaas Kollhof


Need to say that NodeList's items are enumerable, so that for (var x in myNodeList) { } works.
 thank Dethe Elza

rel="" on submit buttons?

what does <label> _mean_? how about an empty one, one which contains
more than one control, no controls?


data: URIs and same-origin policy when navigated to from http:?
 - Hallvord Reiar Michaelsen Steen


need conformance section for editors, which says stuff like "can't be
conforming if editor has an "italics" button"

people want multiline tooltips with explicit line breaks



attributes of type ID that have no value beyond the empty string do
not give the element an ID of "".


ability for a web app to save a file to the local disk:
   var file = window.openFile(); // throws up UI
   file.read();
   var file = window.saveAsFile(); // throws up UI
   file.write();
...or something? Or use data: URIs and right-click-to-save?

http://lxr.mozilla.org/mozilla/source/dom/public/idl/html/nsIDOMNSHTMLDocument.idl


  <p><em>This section is non-normative.</em></p>


how to handle 404s and 500s and other non-OK responses when it comes
to <script>, <link>, <style>, etc.


normative classes:
  -example
  -note
  -warning
  -issue
  hCard, hCalendar
  wiki based registration, first come first served
   * class:
   * applies to elements:
   * processing model:
   * status:


<Hixie> vlad: you should define what the UA should do with out-of-order aDATs
<pav> its an error
<pav> pretty sure we say that somewhere
<Hixie> yes i know it's an error
<Hixie> but that doesn't say what the UA should do
<pav> error == image is invalid
<vlad> yep
<vlad> either broken image icon
<vlad> or display first frame (fall back to normal PNG)
<vlad> up to the UA
<Hixie> right
<Hixie> you should say which one
<pav> its up to the UA
<Hixie> why?
<vlad> "SHOULD display the first frame, but MAY display broken image icon if that's not convenient", in rfc parlance
<vlad> because it's not useful to specify that, IMO
<Hixie> up to the UA means one UA will implement something, it'll become a popular UA, then all the others will have to copy it.
<vlad> how a UA wants to handle image errors is up to the UA
<pav> we're designing an image format, not the html image tag
<pav> the html spec should say what to do with it


should we say that elements in HTML must be lowercase? (but with error
handling for uppercase tags, obviously)? If so, update examples.

<title> is for out of context headers
<h1> is for in-context headers

The parsing rules of HTML

media="" is case-insensitive
case-sensitivity of other attributes, and what it means

empty title attribute is equivalent to missing attribute for purposes
of alternate style sheet processing


<p>s that contain <ul><ol><table><dl><blockquote>? (did we get all those?)



> I'd like search engines to be able to show me the title of a page in the
> same consistent position in a search result, and the name of the site
> (if available) in the same consistent position in a search result, and
> the name of the author (if available) in the same consistent position in
> a search result.
>  
> For that to happen, it would help slightly if the HTML specification
> stopped SHOULD-ing the current <title> behavior. It would help more if
> the HTML specification contained clear, straightforward markup for
> author and site name (and encouraged UAs to present this information   
> when the document is taken out of context).

   <title site="" publisher="" author="">Page Title</title>
   <title>Page Title - <site></site> - <author></author> (<publisher></publisher>)</title>

   <title>Page Title</title>
   <link rel="top" title="" href="">
   <link rel="publisher" title="" href="">
   <link rel="author" title="" href="">


 h1 is styled appropriately, h2 to h6 are styled according to legacy.


[onclick] should make element focusable; enter should send onclick

define implied <html>, <head>, <body>, <p>, </p>, etc.

http://www.aujsproduction.com/samples/wishlist/revampedselector.asp


interactive elements can't be nested (as in <a><button><input></button></a>)


need a summary of all the content models and how they interact:
   a | interactive strictly inline-level element   | where inline-level content is expected | strictly inline-level content  | interactive elements must not be nested
   i | strictly inline-level element               | where inline-level content is expected | strictly inline-level content  |
  em | strictly inline-level element               | where inline-level content is expected | inline-level content           |
   p | block-level element, structured inline-     | where block-level content is expected, | inline-level content           | must not be nested
     | level element                               | where inline-level content is expected |                                |
...etc


need a summary of the differences between the HTML and XML serialisations.
e.g. how <p><ul> is allowed in one but not the other



Google suggest: oninput -> submit a form whose only contents is the
drop down list which you refresh (<datalist>).

Inline editing of <select multiple=""> boxes

image buttons shouldn't be used unless you want the coordinate

need for the spec to say something about sending proprietary data over
the network, e.j. in XMLHttpRequest and other data streams. Is it ok,
if the page is doing the translation?

built-in spell-checking in <input type="text">, <textarea>

author-driven highlighting of individual words in text fields


support access Array element via () instead of [] (IEism)
- https://bugzilla.mozilla.org/show_bug.cgi?id=289876


atom can do this:
       <author>
         <name>Mark Pilgrim</name>
         <uri>http://example.org/</uri>
         <email>f8dy@example.com</email>
       </author>
       <contributor>
         <name>Sam Ruby</name>
         <uri>http://intertwingly.net/blog/</uri>
       </contributor>
how do we do this in HTML5? (what's the use case?)

how to interpret an HTML5 document for syndication
http://hixie.ch/specs/hsf/hsf



section "rendering HTML" has to cope with:
 <q> element's quotes
 <section> <h1>
 default margins and paddings for <ul>, <form>, etc.

  <h4>The <code>q</code> element</h4>
  <p class="big-issue">Need to deal with the quotemark problem without
  adding verbose markup, breaking existing documents, or adding
  redundant elements.</p>



<Hixie> here's how <object> works (assuming you don't support ActiveX)
<Hixie> 1. look at the data="" attribute. If it's not there, go to the step i'll label "bail" below.
<Hixie> 2. fetch the file indicated by the data="" attribute.
<Hixie> 3. while waiting for the MIME type, treat <object> as a replaced element of transparent nothingness, intrinsic size zero.
<hyatt> (so we would honor width/height)
<hyatt> (because it's replaced)
<Hixie> (yes)
<Hixie> 4. if the MIME type is a long time coming (e.g. DNS is being slow) then jump to the "bail" step below until you have the MIME type, then jump back to step 5.
<Hixie> 5. Once you have the MIME type, examine it. If it's a plugin type, jump to the plugin step below. If it's an image, jump to the image step below. If it's a document type (HTML, XML, etc) jump to the iframe step below. Otherwise, you don't recognise it, and jump to the "bail" step.
<Hixie> plugin step: collect all the <param> element children in the <object>. instantiate the plugin and pass the params to it.
<Hixie> image step: render the <object> as if it was an <img>
<Hixie> document step: render the <object> as if it was an <iframe>
<Hixie> bail step: render the <object> as if it was a <span>
 - if there is no authoratative MIME type, then use the type="" attribute.
 - if type="" is something you know you don't support, you MAY not download it
 - if type="" is dynamically changed, do nothing
 - if data="" is dynamically changed, redo loop

<hyatt> apparently your url can come from <param>
<hyatt> not just the data attribute
<hyatt> our code looks for params with "src", "movie", "code" and "url"
<hyatt> and also tries to find the type on a param
<Hixie> oh that's you trying to have hacky activex support
<Hixie> opera does that too
<hyatt> yeah we support activex versions of plugins that are common
<hyatt> like flash and quicktime and realaudio
<Hixie> that would be a step 1b. if no data attribute, then look for a <param> to get you a URL instead.
<Hixie> and if you find one, carry on as if that was your data="".


should have some text talking about the fact that it's ok if your page
passes through a period of non-conformance while script is running,
but that in between scripts it should be compliant.


how to handle 205 reset content responses and other HTTP codes in
response to link clicks, link clicks with target="" attributes,
window.open(), the user typing a URI in the URL bar, etc.

XXX Native code for fast sorting of many data?

http://www.microsoft.com/mind/1097/directanim.asp


events: onmousewheel
<hyatt> with a wheelDelta field on the WheelEvent (whcih comes off UIEvent)
<hyatt> but in OS X you can wheel horizontally 
<hyatt> so we actually added wheelX, wheelY, and wheelZ
<hyatt> with wheelDelta just mapping to wheelY for WinIE compat
<Hixie_> oh i don't mind wheelZ, maybe we can even say ctrl+wheel should map to it on some platforms (windows)
<hyatt> but if you hold down Shift+mouse wheel in mac apps on os x you'll wheel horizontally
wheelDelta is multiples of 120
http://msdn.microsoft.com/workshop/author/dhtml/reference/properties/wheeldelta.asp

events:
http://damowmow.com/temp/safari/WebCore-315/khtml/ecma/kjs_events.cpp

Need to resolve whether <a rel=""> should affect an out-of-band UI (or
whether it should just be a may), see
https://bugs.opera.com/show_bug.cgi?id=169791


should have appendix listing what was already implemented
- http://www.xml.com/pub/a/2005/04/27/deviant.html

| Hixie and Steven shared an item: in both XHTML2 and HTML5, it will
| be possible to have a list child of a paragraph. That's good, from a
| structural point of view. But that's bad, from a user's point of
| view. Imagine you have a paragraph, with red background color. And
| you have an unordered list in your clipboard. You place the caret at
| the end of the paragraph and paste your list. Where does it end up?
| In the paragraph or after it? Red background or not? I really fear
| that, once again, document model authors are completely neglecting
| the authoring side.
 - http://www.glazman.org/weblog/dotclear/index.php?2005/05/27/1055-adam-2

need to define how to process MIME types in <style> and <script> and so forth.

http://www.paulgraham.com/popular.html



  <p>In the ECMAScript DOM binding, objects implementing this interface
  can also be dereferenced using square bracket notation (e.g.
  <code>foo[1]</code> or <code>foo["bar"]</code>). Dereferencing with
  an integer index is equivalent to invoking the <code>item()</code>
  method with that index, and dereferencing with a string index is
  equivalent to invoking the <code>namedItem()</code> method with that
  index.</p>


"you have mail": bubble notification; flash taskbar button, 
=> how do you stop advertisers?



events should bubble from documents to Window

say something about events fired on <body> -> document -> window, like
onload? onpopstate is defined as body->html->doc->window; as is the
local storage event. What about the old ones, how do they work? load,
error, scroll, resize, etc?

If we assuming that bubbling events bubble from document to window,
then it seems reasonable for scroll events that bubble to be fired at
the document if the window is resized, and scroll events that don't
bubble to be fired at elements if they are scrolled. window.onscroll
and document.onscroll should both work.


[HIT TESTING TRANSPARENCY]
Definition: IE considers a point of an element "transparent" if any
one of the following are true:

 1. All of the following are true:
    a: The computed value of 'background-image' is 'none', and
    b: The computed value of 'background-color' is 'transparent', and
    c: The point is over a pixel of an AlphaImageLoader filter image
       that has an alpha value of 0 (fully transparent), or the
       element does not have an AlphaImageLoader filter applied;

 2. The point is outside the element's CSS clip rectangle;

 3. The computed value of 'visibility' is 'hidden';

 4. The element is a transparent IFRAME (in IE, an IFRAME with the
    custom attribute "allowtransparency");

 5. The element is an OBJECT with the custom attribute "wmode" set to 
    "transparent" and the point in question is fully transparent.

Given those definitions, when a mouse event occurs, IE finds the
target element as follows:

   A. Take the topmost node that is under the point where the pointer
      was for the event. For CSS boxes, borders, padding areas and
      content areas are considered part of the node, margins and
      leading generated by the 'line-height' property are not.

   B. If there is no node at that point, no event is fired. STOP.

   C. If the node is a text node, then the event is fired at the text
      node's nearest ancestor element node. STOP.

   D. If the node is not an element, assign the node's nearest
      ancestor element node to a variable X. Otherwise, assign the
      element node itself to X.

   E. If the element X is the BODY element or the HTML element and its
      document is not the document of a transparent IFRAME, goto step
      H. Similarly, if the element X is a TABLE element, or is an IMG
      element, goto step H.

   F. If the point where the pointer was is, per the above definition,
      a point that on the element X is transparent, then ignore that
      element and assign the element that is below that element in the
      stacking order to X. If there is no element below X, or if the
      point on X is not transparent and so the previous condition
      doesn't apply, then leave X as is and go straight to step H.

   G. Goto step E.

   H. If the element X is now a BODY or TABLE element, but the element
      assigned to X in step D was some other element, assign the
      element originally assigned in step D back to X.

   I. The event goes to X. STOP




mousedown's default action is focus, so canceling mousedown stops focus transference.
e.g. on http://www.mozilla.org/editor/midasdemo/

xref all the _ERR exceptions to DOM3CORE


<select><option><hr> support


raising an exception when the wrong number of arguments is passed -
is that a language-specific thing, or what?

why |new XMLHttpRequest()| returns an object that .toStrings to
[object XMLHttpRequest], same with new TCPConnection(); what if a
constructor is called without using "new" in JS?


reload: fire an event when "reload" is pressed so that the page can
reload its data instead of the whole page. cancel the event cancels
the HTTP reload. Abuse prevention required, though.


load event: fire on body, document, window? or just let it bubble?


http://msdn.microsoft.com/workshop/author/dhtml/reference/methods/elementfrompoint.asp
http://msdn.microsoft.com/workshop/author/dhtml/reference/methods/showmodaldialog.asp


refs for TCP/IP (rfc793) and IPv6

http://www.joelonsoftware.com/items/2004/06/17.html
http://www.joelonsoftware.com/items/2004/06/18.html


<neutralise> block that kills scripting or anything dangerous?


XXXX need explanation of when to use undo/redo, and when to use back/forward

XXX "alternate style sheet" should be "alternative style sheet"




  <h5>Using the <code>a</code> element with the <code>command</code> attribute</h5>

  <p>If an <code>a</code> element has a <code
  title="command-attribute">command</code> attribute, then:</p>

  <p>If the element's <code>title</code> attribute is absent, then
  when the UA attempts to display the element's hint, it must instead
  use the specified command's Hint.</p>

  <p>Even if the element's <code>href</code> attribute is absent, the
  element must still match the CSS <code>:link</code> or
  <code>:visited</code> pseudo-classes. It must match the
  <code>:visited</code> pseudo-class if the command's action is to
  follow a link that has already been visited by the user, and must
  match the <code>:link</code> pseudo-class otherwise.</p>

  <p>If a <code>DOMActivate</code> event is dispatched on the element
  and is not canceled, and the event has no other default action, and
  the command's Disabled State is false (enabled), then the command's
  Action must be triggered as the default action.</p>

  <p class="note">The <code>DOMActivate</code> event is fired as the
  default action of the <code>click</code> event.</p>

  <p>If the command's Disabled State is true (disabled) then the
  element must be disabled and must therefore match the
  <code>:disabled</code> pseudo-class. UAs should style disabled links
  in such a way as to clearly convey their disabled state.</p>

  <p>The Label, Icon, Checked State and Type facets of the command are
  ignored by the <code>a</code> element (except for <a
  href="#pseudosAndCommands">matching CSS pseudo-classes</a>).</p>

  <h5>Using the <code>button</code> element with the <code>command</code> attribute</h5>

  <p>If a <code>button</code> element has a <code
  title="command-attribute">command</code> attribute, then:</p>

  <p>If the element's <code>title</code> attribute is absent, then
  when the UA attempts to display the element's hint, it must instead
  use the specified command's Hint.</p>

  <p>If a <code>DOMActivate</code> event is dispatched on the element
  and is not canceled, and the event has no other default action, and
  the command's Disabled State is false (enabled), and the button's
  <code>disabled</code> attribute is absent, then the command's Action
  must be triggered as the default action.</p>

  <p class="note">The <code>DOMActivate</code> event is fired as the
  default action of the <code>click</code> event.</p>

  <p>If the command's Disabled State is true (disabled) then the
  element must be disabled. The <code>button</code> element must also
  be disabled if the element's <code>disabled</code> attribute is
  set.</p>
 
  <p>The Label, Icon, Checked State and Type facets of the command are
  ignored by the <code>button</code> element (except for <a
  href="#pseudosAndCommands">matching CSS pseudo-classes</a>).</p>

  <h5>Using the <code>input</code> element with the <code>command</code> attribute</h5>

  <p>If an <code>input</code> element has no <code>type</code>
  attribute and no <code>name</code> attribute, and it has a <code
  title="command-attribute">command</code> attribute, then:</p>

  <p>If the command is of Type "command" then the element must
  generally be styled and behave as if it was of type
  <code>button</code>; if the Type of the command is "radio" then the
  element must generally be styled and behave as if it was of type
  <code>radio</code>; and if the Type of the command is "checkbox"
  then the element must generally be styled and behave as if it was of
  type <code>checkbox</code>.</p>

  <p>If the command is of Type "command" and the element's
  <code>value</code> attribute is absent, then when the UA attempts to
  display the element's caption, it must instead use the specified
  command's Label. The Label facet is ignored if the command is not of
  Type "command".</p>

  <p>The UA may use the Icon facet of the command to render an
  icon in the control, if appropriate for the UI used.</p>

  <p>If the element's <code>title</code> attribute is absent, then
  when the UA attempts to display the element's hint, it must instead
  use the specified command's Hint.</p>

  <p>If a <code>DOMActivate</code> event is dispatched on the element
  and is not canceled, and the event has no other default action, and
  the command's Disabled State is false (enabled), and the element's
  <code>disabled</code> attribute is absent, then the command's Action
  must be triggered as the default action.</p>

  <p class="note">The <code>DOMActivate</code> event is fired as the
  default action of the <code>click</code> event.</p>

  <p>If the command's Disabled State is true (disabled) then the
  element must be disabled. The <code>input</code> element must also
  be disabled if the element's <code>disabled</code> attribute is
  set.</p>

  <p>If the command's Checked State is true (checked) then the element
  must be checked. The <code>input</code> element must also be checked
  if the element's <code>checked</code> attribute is set.</p>




  <p>This element should not be directly displayed. In CSS-aware user
  agents, this should be achieved by including the following rules, or
  their equivalent, in the UA's user agent style sheet:</p>

  <pre>@namespace xh url(http://www.w3.org/1999/xhtml);
xh|command { display: none; }</pre>



  <h5 id="command-with-command">Using the <code>command</code> element with the <code>command</code> attribute</h5>

  <p>If a <code>command</code> element has a <code
  title="command-attribute">command</code> attribute, then:</p>

  <p>If the element's <code>label</code> attribute is absent, then
  when the UA attempts to display the element's caption, it must instead
  use the specified command's Label.</p>

  <p>If the element's <code>icon</code> attribute is absent, then
  when the UA attempts to display the element's icon, it must instead
  use the specified command's Icon.</p>

  <p>If the element's <code>title</code> attribute is absent, then
  when the UA attempts to display the element's hint, it must instead
  use the specified command's Hint.</p>

  <p>If a <code>click</code> event is dispatched on the element and is
  not canceled, and the command's Disabled State is false (enabled),
  and the element's own <code>disabled</code> attribute is absent,
  then the command's Action must be triggered as the default
  action.</p>

  <p>If the command's Disabled State is true (disabled) then the
  element must be disabled. The <code>command</code> element must also
  be disabled if the element's <code>disabled</code> attribute is
  set.</p>

  <p>If the command's Checked State is true (checked) then the
  element must be checked. The <code>command</code> element must also
  be checked if the element's <code>checked</code> attribute is
  set.</p>

  <p>When a <code title="command-element">command</code> element has a
  <code title="command-attribute">command</code> attribute, any <code
  title="attr-command-type">type</code> and <code
  title="attr-command-radiogroup">radiogroup</code> attribute is
  ignored.</p>



  <h4>The 'icon' property</h4>

  <p>UAs should use the command's Icon as the default generic icon
  provided by the user agent when the 'icon' property computes to
  'auto' on an element that either defines a command or refers to one
  using the <code title="command-attribute">command</code>
  attribute.</p>

  <h4 id="pseudosAndCommands">CSS pseudo-classes and commands</h4>

  <p>When an element uses the <code
  title="command-attribute">command</code> attribute, any UI
  pseudo-classes from the following list that apply to the element
  defining the command also apply to the elements that refer to that
  command.</p>

  <dl>

   <dt>:enabled, :disabled</dt>

   <dd>Matches commands whose Disabled State facet is False and True
   respectively.</dd>

   <dt>:checked</dt>

   <dd>Matches commands whose Type facet is either "radio" or
   "checkbox", and whose Checked State facet is true.</dd>

  </dl>



  <p><code>menu</code> elements with explicit <code>label</code>
  attributes, and <code>menu</code> elements following
  <code>menulabel</code> elements, should be hidden. In CSS-aware UAs,
  this effect should be achieved by including the following rules, or
  their equivalent, in the UA's user agent style sheet:</p>

  <pre>@namespace xh url(http://www.w3.org/1999/xhtml);
xh|menu[label], xh|menulabel + xh|menu { display: none; }</pre>

  <p>All other <code>menu</code> elements should be rendered
  identically to <code>ul</code> elements. In CSS-aware UAs, this
  effect may be achieved by including rules similar to the following
  in the UA's user agent style sheet:</p>

  <pre>@namespace xh url(http://www.w3.org/1999/xhtml);
xh|menu { display: block; margin: 0 0 0 40px; list-style: disc; }</pre>




  <h5>Displaying menus</h5>

  <p>When a <code>menu</code> element is activated, the associated
  menu should be constructed and shown. (For details on how a
  <code>menu</code> element can be activated, see the sections on
  <span>menu links</span> and <span>menu bars</span>.)</p>

  <p>The styles applied to each element in the <code>menu</code>
  element, as well as the element itself, may be applied when
  constructing a menu. UAs are recommended to not apply styling to
  context menus and menus for application menu bars, and to only use
  styles for in-page menus.</p>

  <p>If user agents support styling of menus, they should only support
  the '<code>background</code>', '<code>color</code>',
  '<code>border</code>', '<code>padding</code>' and
  '<code>font</code>' properties on menus and menu items. (This list
  might be incomplete; in general, properties that merely affect the
  appearance of the element should work, but properties that affect
  the layout should not.)</p>

  <p>As the user interacts with a menu, the elements from which the
  menu was created should have appropriate pseudo-classes (:hover,
  :focus, :active) applied.</p>

  <p>The menu items must only consider the computed styles of the
  elements from which they were derived, not other elements.</p>

  <div class="example">

   <p>For example, take this menu:</p>

   <pre>&lt;menu&gt;
&lt;li&gt;&lt;command label="a"/&gt;&lt;/li&gt;
&lt;menu&gt;</pre>

   <p>The menu has one menu item, labelled "a".</p>

   <p>Styles applied to the <code>li</code> element in this menu would
   have no effect on the rendered menu, except in so far as styles
   inherit from that element to the <code>command</code> element.</p>

   <p>Styles applied to the <code>command</code> element could affect
   the menu. While the user is hovering over the menu item, the
   <code>:hover</code> pseudo-class matches the <code>command</code>
   element and any appropriate newly matching rules could be
   applied.</p>

  </div>

  <p>When activated from a <span title="menu links">menu link</span>,
  a menu must be placed in an Appropriate Place. Specifically, if the
  <code>a</code> element is displayed as a vertically-stacked box (as
  is typically seen for elements with '<code>display: block</code>',
  '<code>list-item</code>', or '<code>table</code>'), then the menu
  should appear vertically below the element, anchored so that one of
  its top corners coincides with a bottom corner of the box so that
  the menu and the box each have a horizontal sides in common (or a
  bottom corner of the menu coincides with a top corner of the box, if
  there isn't enough room for the menu to drop down); otherwise, if
  the element is displayed as a horizontally stacked box
  ('<code>display: inline</code>', '<code>table-cell</code>', etc),
  the menu should appear to the <em>side</em> of the box in an
  analogous way. If the element is on the right of the page, the menu
  should drop to the left, and vice versa.</p>

  <p>UAs should implement the drop-down behaviour in more
  platform-appropriate ways if the platform conventions differ from
  the behaviour described above.</p>




  <h4>The <dfn title="command-attribute"><code>command</code></dfn>
  attribute</h4>

  <p>Any element that can define a command can also, instead, have a
  <code>command</code> attribute that specifies the ID of a command
  that the element should defer to. In this case the element does not
  define a command, but, in the absence of attributes to the contrary,
  reflects the state of the element specified.</p>

  <p>If the <code>command</code> attribute specifies an ID that is not
  the ID of an element that defines a command, then the
  <code>command</code> DOM attribute is set to the null value, and the
  element acts as if it was linked to an element that defined a
  command with no Label, no Hint, no Icon, no Action, that was not
  Hidden, not Disabled, not Checked, and that was of Type
  "command".</p>


replaceable DOM properties: http://lxr.mozilla.org/mozilla/source/dom/src/base/nsDOMClassInfo.cpp#5928
<       brendan>|Hixie: so yeah, lxr for JSRESOLVE_QUALIFIED

screen object:
screen contains top left width height pixelDepth colorDepth availWidth availHeight availLeft availTop



  <p>The most direct way to represent a command is by using the <code
  title="command-element">command</code> element. A <code
  title="command-element">command</code> element defines a command if
  it does not have a <code title="command-attribute">command</code>
  attribute.</p>

  <div class="example">
   <pre>...
 &lt;command id="c_stop" label="Emergency Stop" onclick="dostop()"/&gt;
 &lt;command id="c_go" label="Go" onclick="dogo()"/&gt;
 &lt;command id="c_lamp" label="Headlamps" onclick="dof2()" disabled="disabled"/&gt;
...</pre>
</div>

  <p>The <code>command</code> element, in addition to the core and
  internationalisation attributes, may have the following
  attributes specified:</p>

  <dl>

   <!-+- yes i know that some of these are core attributes. If you can
   give me a better introductory paragraph, I'm all for it. -+->

   <dt><dfn title="attr-command-type"><code>type</code></dfn></dt>

   <dd>The command's Type. If present, this attribute must either have
   the value <code>radio</code>, in which case the command is of Type
   "radio", or the value <code>checkbox</code>, in which case the
   command is (amazingly) of Type "checkbox". Any other value, or the
   absence of the attribute altogether, means that the command is of
   Type "command".</dd>

   <dt><dfn title="attr-command-id"><code>id</code></dfn></dt>

   <dd>The command's ID. If this attribute is not specified, then the
   command is anonymous.</dd>

   <dt><dfn title="attr-command-label"><code>label</code></dfn></dt>

   <dd>The command's Label. If the attribute is not specified, the
   command's Label is given by the element's <code>textContent</code>
   DOM attribute.</dd>

   <dt><dfn title="attr-command-title"><code>title</code></dfn></dt>

   <dd>The command's Hint. If the attribute is not specified, the
   command's Hint is the empty string.</dd>

   <dt><dfn title="attr-command-icon"><code>icon</code></dfn></dt>

   <dd>A URI to the command's Icon. If the attribute is not specified,
   then the command has no Icon.</dd>

   <dt><dfn title="attr-command-onclick"><code>onclick</code></dfn></dt>

   <dd>An event handler attribute that listens for <code>click</code>
   events.</dd>

   <dt><dfn title="attr-command-hide"><code>hide</code></dfn></dt>

   <dd>The command's Hidden State. If the attribute is present, the
   command is hidden (and also disabled, regardless of the value of
   the <code>disabled</code> attribute), otherwise, the command is
   shown. If the attribute is present, it should have the value
   "<code>hide</code>". <!-+-The name of the attribute reflects the
   fact that Hidden commands in menus are hidden.-+-></dd>

   <dt><dfn title="attr-command-disabled"><code>disabled</code></dfn></dt>

   <dd>The command's Disabled State. If the attribute is present, the
   command is disabled, otherwise, the command is enabled. If the
   attribute is present, it should have the value
   "<code>disabled</code>".</dd>

   <dt><dfn title="attr-command-checked"><code>checked</code></dfn></dt>

   <dd>The command's Checked State. If the attribute is present, the
   command is checked, otherwise, the command is not. If the attribute
   is present, it should have the value "<code>checked</code>".</dd>

   <dt><dfn title="attr-command-radiogroup"><code>radiogroup</code></dfn></dt>

   <dd>An attribute indicating the name of the group of commands that
   will be toggled when the command itself is toggled. (Described <a
   href="#radiocommand">below</a>.)</dd>

   <dt><dfn title="attr-command-default"><code>default</code></dfn></dt>

   <dd>An attribute indicating whether the command is the default
   command. If the attribute is present, the command is the default
   command, otherwise it is not. If it is set, it should have the
   value <code>default</code>. Used by context menus to indicate what
   the default option would be. The :default pseudo-class matches
   <code>command</code> elements with this attribute.</dd>

  </dl>

  <p>In addition, <code title="command-element">command</code>
  elements may also have a <code
  title="command-attribute">command</code> attribute, as <a
  href="#command-with-command">described below</a>.</p>

  <p>The Type, ID, Label, Hint, Icon, Hidden State, Disabled State,
  and Checked State of the command defined by a <code
  title="command-element">command</code> element are as described
  above. The Action of a <code title="command-element">command</code>
  element is that a <code>{null, "click"}</code> event is fired on the
  element.</p>

  <p>If the Type of the command is "checkbox", when a
  <code>click</code> event is dispatched on the element, user agents
  must toggle the value of the <code>checked</code> attribute before
  the event is dispatched in the document. (If the attribute is
  absent, then it is set to the value <code>checked</code>, and if the
  attribute is present, it is removed.) If the default action of the
  event is canceled, the value of the attribute must be changed back
  to the value it had before the event was dispatched.</p>

  <p id="radiocommand">If the Type of the command is "radio", when a
  <code>click</code> event is dispatched on the element, user agents
  must set the value of the <code>checked</code> attribute on the
  element to <code>checked</code>, and remove the attribute from any
  <code>command</code> elements with <code>type</code> set to
  <code>radio</code> and the same parent element and same
  <code>radiogroup</code> attribute, before the event is dispatched in
  the document. (If the element has no <code>radiogroup</code>
  attribute, then the elements "with the same <code>radiogroup</code>
  attribute" are those elements with <em>no</em>
  <code>radiogroup</code> attribute.) If the default action of the
  event is canceled, the value of the attributes that were changed
  must be changed back to the values they had before the event was
  dispatched.</p>

  <p>In HTML the <code>command</code> element is an empty element with
  no end tag.</p>

  <p>Authors should put <code>command</code> elements inside the
  <code>head</code> element, inside any element that may contain
  <span>block-level elements</span> or <span>inline-level
  content</span>, or inside <code>commandset</code> elements.</p> <!-+-
  should, because hey, if they want to put them elsewhere, why not.
  XXX -+->

  <p>Authors should not put elements or text inside
  <code>command</code> elements.</p>




  <p>The <code title="dom-command-ro-command">command</code> DOM attribute
  is defined with the <code title="attr-command">command</code>
  content attribute.</p>


Need to become consistent about whether or not to quote keyword
("<code title="">foo</code>" vs <code>foo</code>)



  XXX command icons in rendering section:

  If the element defining the command has no explicit icon, then the
  attribute must instead return the computed value of the CSS '<code
  title="">icon</code>' property on that element. <a
  href="#refsCSS3UI">[CSS3UI]</a>

  If the computed value of '<code title="">icon</code>' is
  '<code>auto</code>',


search for event-click and make them all point to:
<a href="http://www.w3.org/TR/DOM-Level-3-Events/events.html#event-click"><code>click</code></a>
...or something.

<code>DOMActivate -> <code title="event-DOMActivate">DOMActivate


onclick="" only fires if it is a MouseEvent


<form> .submit definition - see http://lxr.mozilla.org/mozilla/source/content/html/content/src/nsHTMLFormElement.cpp#600
for how to handle multiple calls in series


http://lxr.mozilla.org/mozilla/source/content/html/content/src/nsHTMLFormElement.cpp#699

How events are handled:
http://lxr.mozilla.org/mozilla/ident?i=HandleDOMEvent

http://www.quirksmode.org/js/events_compinfo.html
e.g. mousedown mouseup click mousedown mouseup click dblclick

http://msdn.microsoft.com/library/default.asp?url=/workshop/author/dhtml/reference/events.asp



05:46 <            bz>|Hixie: let's put it this way
05:46 <            bz>|Hixie: 1)  A script is executed when its data is available
05:47 <            bz>|Hixie: 2) The data for an inline script is available when its </script> is seen
05:47 <            bz>|Hixie: 3) The data for a script with src is available when it finishes loading
05:47 <            bz>|Hixie: all good so far?
05:47 <         Hixie>|i'm waiting for the bit where src= causes blocking in the normal, non-d.w case
05:47 <            bz>|Hixie: 4) The data for a script with src starts loading when the <script> node is inserted into the DOM
05:48 <        shaver>|it causes parser blocking in the normal case
05:48 <            bz>|Hixie: 5)  When such a load starts, all further parsing is suspended until the load has completed and the script has executed.
05:48 <            bz>|Hixie: so if we forget document.write
05:48 <            bz>|Hixie: and look at the HTML:  <script src="foo"></script><div>
05:48 <            bz>|Hixie: the text "<div>" will nto be parsed until after the script runs
05:49 <            bz>|Hixie: this is needed so that if the script does document.write that text can be inserted _before_ the "<div>" text into the parser
05:49 <         Hixie>|sure
05:49 <         Hixie>|all this is fine
05:49 <            bz>|Hixie: ok.  So now let's look at our case
05:49 <         Hixie>|but how does document.write() know when to return?
05:49 -!- davel [davel@moz-4F4E281A.dsl.static.sonic.net] has quit [Quit: davel]
05:49 <            bz>|It gives the data to the parser, and tells the parser to parse it
05:49 <            bz>|Once the parser returns, document.write returns
05:50 <            bz>|The parser returns when it runs out of data to parse (it's parsed it all)
05:50 <            bz>|Or if it's explicitly suspended (eg by a <script src="">)
05:50 <         Hixie>|AH
05:50 <            bz>|All this in Gecko
05:50 <         Hixie>|ok that was the key piece of information i was missing
05:50 <         Hixie>|the "explicit suspension"
05:50 <         Hixie>|ok
but test IE on this...


XXX publish a "Valid HTML5!" button with a kitten on it. Made by an artist. (Doodle?)


XXX rename "Block-level" and "inline-level" to something else to
prevent terminology clash with CSS.

   Interaction with document.open/write/close is undefined
   How to determine the character encoding
   Integration with quirks mode problems
   <style> parsing needs tweaking if we want to exactly match IE
   <base> parsing needs tweaking to handle multiple <base>s
   <isindex> needs some prose in the form submission section
   No-frames and no-script modes aren't yet defined
   Execution of <script> is not yet defined
   New HTML5 elements aren't yet defined
   There are various cases (marked) where EOF handling is undefined
   Interaction with the "load" event is undefined


hsivonen:
> To make document conformance a more useful concept for the purpose of catching
> author errors, I suggest that the following attributes be made required:
> href and rel on link
> href on base
> name and content on meta (other than the encoding decl)
> src on img
> code, height and width on applet
> name and value on param
...
> To allow user agents see whether the author provided the empty string as the
> alternative text of whether the author just didn't care, I suggest that the
> alt attribute on img be made optional.
(i agree -ian)
...
> On the other hand, I have doubts about the requirement of significant
> inline content. When the W3C said that paragraphs mustn't be empty,
> various applications started emitting <p>&nbsp;</p>. If the WHAT WG says
> that paragraphs must contend significant inline content, are the
> developers of those applications suddenly going to decide not to allow
> them to paragraphs to be saved or are they going to come up with an even
> more crufty work-around to comply with the machine-checkable
> requirements of the spec?
(i agree, i think we should drop "significant inline content". -ian)


bjoern:
> If the concern here is what the specification should say, then that's
> what a valid state is, not what a valid document is, since the class of
> "predictably valid" documents does not cover many dynamic documents.



arv asks for: a way to track download progress of, e.g., images when
you are preloading 10 images; cf onprogress on XHR in mozilla


window.getAttention() or some similar API to let the user know the
page wants attention? How do you reduce the chance of irritation?
see also https://bugzilla.mozilla.org/show_bug.cgi?id=293412




ITEM

Items have:
 - parents, children
 - properties
 - commands that can apply to them



   <li>Inline markup for pop-up windows, for example for dialog boxes
   or tool palettes, so that dialogs need not be defined in separate
   files.</li>

   <li>Command updating: applications that have several access
   points for the same feature, for instance a menu item and a
   tool-bar button, would benefit from having to disable such
   commands only once, instead of having to keep each access point
   synchronized with the feature's availability at all times.
   Similarly menu items or tool-bar buttons that represent a toggle
   state could automatically stay synchronized whenever
   toggled.</li>

   <li>More device-independent DOM events: The DOM event set needs
   device-independent events, such as events that fire when a button
   or link is activated, whether via the mouse or the keyboard.
   <code>DOMActivate</code> is a start, but it lacks equivalent HTML
   attributes, and additional events may be needed.</li>

   <li>Richer widget set: the existing HTML controls are quite
   limited, some controls for commonly used types such as date
   controls and range controls would be useful.</li>

   <li>Sortable and multicolumn tree views and list views with rich
   formatting.</li>

   <li>Ability to define custom widgets cleanly, for example using
   XBL and APIs to query and control focus state, widget state, the
   position and state of input devices, etc.</li>

   <li>Rich text editing: an underlying architecture upon which
   domain-specific editors can be created, including things like
   control over the caret position.</li>

   <li>A predefined HTML editor based on the rich text editing
   architecture.</li>

   <li>Drag and drop APIs.</li>

   <li>Text selection manipulation APIs.</li>

   <li>Clipboard APIs (if the security and privacy concerns can be
   addressed).</li>

   <li>Flexible box model: The existing box model in CSS is designed
   largely for documents rather than user interface. We need a new
   box model designed for user interface which would relieve author
   complaints about other aspects of CSS and also reduce the need
   for tables for layout.</li>

   <li>Window-based state management (so that new windows don't
   interfere with existing sessions), for example implemented as a
   per-domain, per-window "file system". This would allow multiple
   instances of the same application (from the same site) to run
   without the instances overwriting each other's cookies.</li>

   <li>Markup to denote <span>mutually exclusive sections</span> (as
   in the commonly seen wizard interfaces).</li>

   <li>An improved CSS object model, for example with better APIs
   for animation, simpler ways to navigate the rendered content, a
   way to find the position of an element, methods to list the
   elements under a coordinate, etc.</li>

   <li>Better defined user authentication state handling. (Being able
   to "log out" of sites reliably, for instance, or being able to
   integrate the HTTP authentication model into the Web page.)</li>


offline storage / caching pining:
http://groups.google.com/group/mozilla.dev.platform/browse_frm/thread/bf866101aa238773/a298294c27b9380a?lnk=gst&q=offline&rnum=1#a298294c27b9380a


DOM0 quirks that Mozilla knows about:
http://lxr.mozilla.org/seamonkey/source/dom/src/base/nsDOMClassInfo.cpp



mutually exclusive sections:
  <p class="example">For example, in an application for an online
  mutiplayer game, there could be four mutually exclusive sections:
  one for the login page, one for the network status page displayed
  while the user is logging in, one for a "lobby" where players get
  together to organise a game, and one for the actual game. The
  different sections are the various states that the application can
  reach.</p>


XXX make a consistent decision of which of the following formats to use:

    U+1234 FOO BAR character ("foo")
    U+1234 FOO BAR character ('foo')
    U+1234 FOO BAR character (foo)
    U+1234 FOO BAR ("foo") character
    U+1234 FOO BAR ('foo') character
    U+1234 FOO BAR (foo) character
    U+1234 FOO BAR character ("<code title="">foo</code>")
    U+1234 FOO BAR character ('<code title="">foo</code>')
    U+1234 FOO BAR character (<code title="">foo</code>)
    U+1234 FOO BAR ("<code title="">foo</code>") character
    U+1234 FOO BAR ('<code title="">foo</code>') character
    U+1234 FOO BAR (<code title="">foo</code>) character

And make these match:

    0x12 (ASCII FOO)
    0x12 (ASCII "foo")
    0x12 (ASCII 'foo')
    0x12 ("foo")
    0x12 ('foo')

-->
  <script src="http://status.whatwg.org/annotate-web-apps.js"
  type="text/javascript"></script>
generated by cgit v1.2.3 (git 2.39.1) at 2024-04-24 10:18:44 +0000