SVG clip-path, mask and filter for non-SVG content

As I mentioned a while ago, I'd like to see the 'clip-path', 'mask' and
'filter' CSS properties extended to apply to non-SVG content. I think the
SVG WG is the best place to do that, because the SVG spec defines those
properties.

I've updated my proposal to remove everything other than the changes to
those three properties:
http://people.mozilla.com/~roc/SVG-CSS-Effects-Draft.html

The code to implement this change has actually landed on Firefox trunk.
There is still a while before a new Firefox release, so there's time to
update the behaviour based on feedback or even remove it or change syntax if
necessary. This is simple stuff with not many degrees of freedom so I'm
hopeful we can get some consensus.

Please consider this proposal and let me know what you think.

Rob
-- 
"He was pierced for our transgressions, he was crushed for our iniquities;
the punishment that brought us peace was upon him, and by his wounds we are
healed. We all, like sheep, have gone astray, each of us has turned to his
own way; and the LORD has laid on him the iniquity of us all." [Isaiah
53:5-6]