>>697
その辺使ってないけど無理みたいよ
http://stackoverflow.com/questions/1082474/authoring-html5-in-emacs

But HTML5 is not XML. You have two alternatives, use HTML5 with its proper
syntax or using XML with the grammar of HTML5 (as XHTML).
In the first solution the code <input type=text name=foo required> is correct,
but the XML way is <input type="text" name="foo" required="required" />.