307171 2026-02-06 08:51:41 -0800 Anchor positioning: abspos elements can anchor to viewport-fixedpos elements 2026-06-06 12:54:27 -0700 1 1 1 Unclassified WebKit Layout and Rendering Safari Technology Preview Unspecified Unspecified RESOLVED FIXED InRadar P2 Normal --- 291856 1 dshin fantasai.bugs bfulgham fantasai.bugs kiet.ho simon.fraser webkit-bug-importer zalan oldest_to_newest 2178797 0 478269 dshin 2026-02-06 08:51:41 -0800 Created attachment 478269 Minimum Reproducible Case (Discovered from Firefox bug: https://bugzilla.mozilla.org/show_bug.cgi?id=2014997) Given that: 1. The initial fixed containing block is the parent of the initial containing block in the containing block chain [1], 2. Absolute containing block can have at most the initial containing block as its absolute containing block, 3. And an acceptable anchor should be strictly laid out before the positioned element [2], Strictly spec-wise, fixed elements (Using the initial fixed containing block) should not be a valid anchor for an absolute positioned element in the testcase. Perhaps relatedly - the positioned element doesn't seem to be properly scroll (un?)compensated. [1] https://drafts.csswg.org/css-position-3/#def-cb [2] https://drafts.csswg.org/css-anchor-position-1/#acceptable-anchor-element 2181315 1 webkit-bug-importer 2026-02-13 08:52:10 -0800 <rdar://problem/170323196> 2189646 2 pascoe 2026-03-12 11:08:50 -0700 Pull request: https://github.com/WebKit/WebKit/pull/60480 2189649 3 dshin 2026-03-12 11:12:01 -0700 There's a proposed spec change to in fact get rid of the special fixed ICB, which would allow this behaviour: https://github.com/w3c/csswg-drafts/issues/13468 2216547 4 fantasai.bugs 2026-06-01 16:31:50 -0700 Pull request: https://github.com/WebKit/WebKit/pull/66208 2218308 5 ews-feeder 2026-06-06 12:54:25 -0700 Committed 314706@main (fe7bcd9ee8c2): <https://commits.webkit.org/314706@main> Reviewed commits have been landed. Closing PR #66208 and removing active labels. 478269 2026-02-06 08:51:41 -0800 2026-02-06 08:51:41 -0800 Minimum Reproducible Case fixed.html text/html 406 dshin PCFET0NUWVBFIGh0bWw+CjxzdHlsZT4KLmNiIHsKICB3aWR0aDogMTAwcHg7CiAgaGVpZ2h0OiAx MDBweDsKICBvdmVyZmxvdzogc2Nyb2xsOwp9CgouZml4ZWQgewogIHBvc2l0aW9uOiBmaXhlZDsK ICBsZWZ0OiAwcHg7CiAgdG9wOiAwcHg7CiAgYm9yZGVyOiAxcHggc29saWQ7CiAgYW5jaG9yLW5h bWU6IC0tYTsKfQoKLmFicyB7CiAgcG9zaXRpb24tYW5jaG9yOiAtLWE7CiAgcG9zaXRpb24tYXJl YTogYm90dG9tIHJpZ2h0OwogIHBvc2l0aW9uOiBhYnNvbHV0ZTsKICBib3JkZXI6IDFweCBzb2xp ZDsKfQo8L3N0eWxlPgo8ZGl2IGlkPWYgY2xhc3M9Zml4ZWQ+QW5jaG9yPC9kaXY+CjxkaXYgaWQ9 YSBjbGFzcz1hYnM+UG9zaXRpb25lZDwvZGl2Pgo8ZGl2IHN0eWxlPSJoZWlnaHQ6IDIwMHZoOyI+ PC9kaXY+Cg==