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+LibNSLayout Architecture
+`LibNSLayout` is a library for performing layout on a Document Object Model
+for HTML. Its purpose is to allow client applications to provide DOM
+information and convert that into a render list, which can be displayed
+by the client.
+Clients of `LibNSLayout` must use the following additional libraries, because
+their types are used in the `LibNSLayout` interface:
+* `LibDOM` is used to provide the DOM interface.
+* `LibCSS` is used to provide the CSS handling.
+* `LibWapcaplet` is used for interned strings.
+The devision of responsibilities between `LibNSLayout` and its clients are
+as follows:
+### Client
+* Fetching the document to be displayed.
+* Creating a CSS selection context (with default user-agent, and user CSS).
+* Generating DOM.
+* Creating a `LibNSLayout` layout for the document, passing the DOM document,
+ CSS selection context, and appropriate CSS media descriptor.
+* Listening to DOM changes.
+ * Fetching resources needed by DOM.
+ * CSS (STYLE elements, and LINK elements):
+ * Parsing the CSS.
+ * Updating CSS selection context as stylesheets are fetched,
+ and notifying `LibNSLayout`.
+ * JavaScript (SCRIPT elements, and LINK elements)
+ * Executing JavaScript.
+ * Favicons (LINK elements.)
+ * Images, Frames, Iframes.
+ * Notifying `LibNSLayout` of DOM changes.
+* Performing resource fetches on behalf of LibNSLayout.
+ * (Such as when LibNSLayout requires a background image or web font for
+ an element due to CSS.)
+* Asking `LibNSLayout` to perform layout.
+ * Displaying the returned render list.
+* Asking `LibNSLayout` for layout info (e.g. due to JavaScript.)
+* Passing mouse actions to `LibNSLayout`.
+* Passing keyboard input to `LibNSLayout`.
+* Measuring text???
+### `LibNSlayout`
+* Creates a layout object that's opaque to the client, and returns its
+ handle.
+* Performs CSS selection as appropriate when DOM changes.
+* Asking client to fetch a resource that's needed for a computed style.
+* Performs layout (if required) when asked by client and returns render list.
+* Performs layout (if required) when asked by client for layout info.