The HTML 5 DTD project Posted by cosmohh on Tuesday May 31, 2011 @06:04AM from the html5dtd.org dept. http://www.html5dtd.org/faq/ ( 4 comments | 10 points | on HN )
This seems like a failing of Emacs+PSGML rather than HTML5 lack of DTD.
Or rather why are you using an SGML tool to write a language not based on SGML? (from wikipedia "The HTML5 syntax is no longer based on SGML")