Multiargument :is() can't be supported (it would require multiple hashes) but a trivial one can. This may be important for nesting.
<rdar://problem/104425645>
Pull request: https://github.com/WebKit/WebKit/pull/8833
Committed 259089@main (711c7abb5e9b): <https://commits.webkit.org/259089@main> Reviewed commits have been landed. Closing PR #8833 and removing active labels.