[bowlich]

I've thought before that it would be neat to have the ability to specify an alternative markup inside any element. A kind of:

<div markup="markdown">Browser now _interprets_ content as markdown until end of div.</div>

It would make user-submitted content so much better since you could just directly embed bbcode, markdown, etc. without needing to parse it to html or validate that their submission is valid html/only using approved tags, etc.