Looks good -- the highlighting is definitely imperfect, but it's clearly better than nothing.

The biggest problem seems to be around CF tags that don't require a close tag -- you get a lot of close tags highlighted in red because CodeMirror thinks you skipped one. The HTML highlighter has a hardcoded list of the tags it expects to have no closing tag, and unfortunately it doesn't look like the list is configurable (see the top of xml.js). It would be an awesome contribution back to CodeMirror to add config options for that, and then you could leverage it to improve the CF highlighting. Interested? :-)

This is certainly a reasonable start though. I'll merge it now.