https://drafts.csswg.org/css-contain-3/#container-name
Created attachment 449906 [details] Patch
Created attachment 449907 [details] Patch
Committed r288556 (246387@main): <https://commits.webkit.org/246387@main> All reviewed patches have been landed. Closing bug and clearing flags on attachment 449907 [details].
<rdar://problem/88026745>