I have not used it yet so I can’t comment on that.
Facelets support should include tag completion and context assist, of course (list of attributes when you start a tag, list attribute values if they are an enumeration). It’s also very important to support EL (offer bean names/methods, etc). It’s imperitive that the various template mechanisms be supported intelligently in the editor (offer file names in the src/template attributes, and EL should list not only managed beans but also attributes used when invoking the tag file).
For instance, if a page calls a custom tag file with:
<b:customTag passedValue=”cheese”/>
then EL assist in the custom tag file should offer the passedValue attribute in addition to managed bean names.
On that note, context assist that supports custom tags and custom tag files would be nice.
If you have a chance, read Rick Hightower’s JSF blog entries as he articulates a lot of interesting uses for facelets that should be properly supported in any facelets oriented XHTML editor ( http://jroller.com/page/RickHigh ).