Efficient invalidation for these is difficult so disallow them for now. See https://github.com/w3c/csswg-drafts/issues/6952 for more details
Created attachment 449167 [details] Patch
Created attachment 449320 [details] Patch
Committed r288111 (246125@main): <https://commits.webkit.org/246125@main> All reviewed patches have been landed. Closing bug and clearing flags on attachment 449320 [details].
<rdar://problem/87699260>