Since I sent the intent to prototype (below), there's been a bunch of
spec work and discussion, lots of tests written, and I think we have a
fairly complete implementation.
Tests for this are in https://wpt.fyi/results/css/css-cascade
, and there
are only two categories of tests we fail (once the tests get updated for
the patches that landed today):
* Tests that test stuff that we don't implement or enable by default
(like constructable stylesheets / @property).
* Tests for one animation edge case that we fail for the regular
`revert` keyword as well and which we've shipped for a long while.
So if all goes well, I want to enable this feature by default for
Firefox 97. Let me know if there's any concern with that.