There are two kinds of links which we should support:
1. External HTML links (<a href="http://..."> or <a href="https://...">). Such links are supposed to be opened in the default web browser:

Note: we don't have such links in our content assist. This screenshot is just an example how it will look like if we add any <a> to a description message.

2. Internal links to JavaElement (used in JSF EL). It works in the same way as Eclipse JDT content assist does. Such links are supposed to be opened in SWT web browser (in the same description window):

Steps to test:

1. Make sure JDK sources are available in Eclipse
2. Create a JSF 2 KickStart project.
3. Open greeting.xhtml
4. Type #{user.name.l and press Ctrl+Space
5. Select length
6. There should be a description dialog with javalement links to length() and CharSequence: