Willful Violation of the Spec
At the present time, the front page of my weblog does not validate. From what I can tell, I am using an extension point in a manner totally consistent with the intent of that grammar, and in a way that produces useful results, at least with Firefox. My only sin is that I’m using that attribute in a way that was unanticipated by the authors of the SVG.
From what I can tell, the HTML5 specification doesn’t have much to say on the matter.