We already don't validate. There's no point to
trying to conform to a
validator when the spec/validator is wrong. And we already have cases like
that.
I think we should try to validate though mostly for future proofing...
Anyways, technically you could already use scoped
anyways. Just add the
scoped attribute. Don't use css that applies outside the content area. And
then it'll validate, it'll work in browsers, and when browsers actually
implement scoped they'll start restricting the scope.
<snip>
But after you've dealt with all the XSS issues;
you've opened up the ability
to completely destroy the UI from within WikiText. In ways even worse than
the tricks attempting to simply cover the whole UI with a div. Those tricks
being ones you could technically eliminate by using overflow+relative on the
content area and disallowing position: fixed; (The only thing in the way of
that right now is WP's stupid page icon hack).
I think if we restricted css to templates that only trusted admins can
edit then these problems goes away somewhat no?