You may be interested to know that Michael Sheets has been working on an XHTML strict syntax which not only mark up every single tag/ attribute, but also marks up invalid stuff (like badly nested tags, text where no text is allowed etc.)
It's in the Experimental HTML bundle at the repository, but it'll be included when he gives the green light.
WOW! That is a humongous task, and one that will be great once it's done I'm sure :) Is it possible to get it from somewhere over at http://anon:anon@macromates.com/svn/Bundles/trunk/ ?
Andreas