Missing for me are:
- XHTML support, for example properly closing tag like <br />
I use psgml in combination with MMM -- see the instructions here:
http://www.emacswiki.org/cgi-bin/wiki/HtmlModeDeluxe
Getting psgml up and running -- especially getting the W3C DTDs (why
oh why don't they make them all available in a single package) is a pain
but very much worth it. Read up about psgml (use google) -- and if you're
still interested and want some help using it for (X)HTML editing then drop
me an email (if you just post to the NG I may miss it) and I can help you
out (e.g. send you all the relevant DTDs, send you the relevant bits of my
.emacs, etc.).