I honestly don't see much gain in it. Html that is regular enough to be worth doing this to would be better served in XML. Html that isn't so regular still wouldn't match well even with your theoretical grammar.

Html is too irregular to treat in a regular manner and the benefit is too low. Thus the people that most wanted this sort of thing, (like /.'s slashboxes and such) tended to encourage more regular standards in order to get what they wanted without ad-hoc parsing that needs to be tweaked every week or month.

Still, if you take a stab at it, I'll tinker with it. It's an interesting example of what Larry Wall has been calling "little languages". Yah never know, you might open up some flood gates and set a buncha people off in a direction you never expected.

--
$you = new YOU;
honk() if $you->love(perl)