Standards vs Best Practices

I can do some very inaccessible things in HTML5 that won’t trigger validity warnings, because the standards writers just didn’t think those issues mattered very much.

Marc Drummond is concerned about the progress of HTML5 away from enforcing good accessibility practices. 

So far HTML5 has been aggresively pragmatic to ensure it was a standard that would actually be adopted. See the justification for when Ian Hickson chose not to define a video codec in HTML5 because regardless of what he chose, not all vendors would implement it. 

Wherever it’s possible, HTML5 should not prevent people from writing accessible websites and applications. That said, validators and technical specifications cannot enforce best practices for writing accessible or usable websites. People need to do this.