A content extension is either a contribution of content into a known anchor (similar to an extension into an extension point), or the replacement of an existing element in a document.
Anchor elements (e.g. <anchor id="my_anchor"/>) can be
specified in any user assistance XML document, and represent places at
which other components are allowed to extend this document. Specifying an
anchor is as simple as adding the element in your markup.
To contribute content into an anchor, you must write the content to be
added in a separate XML file and hook it into the platform using one of
two extension points. For help or cheat sheet content, you must use the
org.eclipse.help.contentExtension extension point. For
welcome (intro) extensions, use
org.eclipse.ui.intro.configExtension. The table of
contents markup also allows the special constructs link and link_to which perform a
similar function to includes and contributions, but perform the
additional operation of merging extra documents to index for searching.
For example, let's say component A's documentation provides a listing of file formats it supports. If component B extends A's support to several more formats, you can place an anchor in A's list, and extend the list from B. For example:
<p>The following list shows the supported formats:</p>
<ul>
<li>Portable Network Graphics (.png)</li>
<li>Joint Photographic Experts Group (.jpeg)</li>
<li>Graphical Interchange Format (.gif)</li>
<!-- Extra formats go here -->
<anchor id="image_format_list"/>
</ul>
Then component B can make a contribution to the anchor to add more formats to the list by specifying the following extension:
<extension point="org.eclipse.help.contentExtension">
<contentExtension
file="path/to/extension.xml"/>
</extension>
Where the file path/to/extension.xml might contain:
<contentExtension>
<contribution
content="docs/mydoc.xhtml#mycontent"
path="/component_a_plugin/docs/doc_with_anchor.xhtml#anchorId">
</contribution>
</contentExtension>
The element with the id attribute mycontent in
document docs/mydoc.xhtml would contain the content you wish
to contribute into the anchor. The result will be that when the user
views the document, the extra content will appear at the anchor as though
it was explicitly added into the original document.
Any XML element in a user assistance document that has an id
attribute that is unique to that document can be replaced with any other
element.
As with contributions into anchors, to replace an element, you must write
the new element to replace with in a separate XML file and hook it into
the platform using one of two extension points. For help or cheat sheet
content, you must use the
org.eclipse.help.contentExtension extension point. For
welcome (intro) extensions, use
org.eclipse.ui.intro.configExtension.
The only difference with replacements as opposed to contributions into
anchors is the name of the XML element used in the markup; use the
replacement element instead of contribution (or
replacementContent in the case of welcome). For example:
<contentExtension>
<replacement
content="docs/mydoc.xml#myelement"
path="/plugin.id/path/doc.xml#elementId">
</replacement>
</contentExtension>
(Note the markup is different for welcome, as specified in the
org.eclipse.ui.intro.configExtension extension point)
The format of the path attribute is
/pluginId/path/file.xml#elementId, except welcome where it
is pageId/path/to/elementId where the pageId is the welcome
page id, and all other path segments are ids of container elements like
groups, leading to the target element.