From the HTML 5 specification:
Authors must not use elements, attributes, or attribute values for purposes other than their appropriate intended semantic purpose. Authors must not use elements, attributes, or attribute values that are not permitted by this specification or other applicable specifications.
How about complementing that with:
HTML5 specifiers must think of absolutely everything an author might need to implement and provide them the most convenient and perfect and entirely appropriate elements, attributes and attribute values to implement it with.
Mind you, given how long they’ve been mashing away on HTML 5… I think they think they’re doing that.