Not sure why tbh, but Chrome & Edge also fail here. Only Firefox passes.
https://github.com/web-platform-tests/wpt/blob/master/css/css-will-change/will-change-fixpos-cb-position-1.html
<rdar://problem/77958400>
I got some clarification from Emilio: No value of `position` triggers a containing block for a position: fixed; child element, so `will-change: position` also shouldn't trigger a containing block.
Created attachment 428779 [details] Patch
Comment on attachment 428779 [details] Patch View in context: https://bugs.webkit.org/attachment.cgi?id=428779&action=review > Source/WebCore/ChangeLog:8 > + Marked relevant WPT as pass. Please write more words here about how you are undoing a previous change. Reference that other commit, and reference the test that is exercising the change.
Created attachment 428791 [details] Patch
Created attachment 428792 [details] Patch
Created attachment 428793 [details] Patch
Committed r277579 (237806@main): <https://commits.webkit.org/237806@main> All reviewed patches have been landed. Closing bug and clearing flags on attachment 428793 [details].