[css-flexbox] align-content behavior does not match the spec for absolutely positioned children

• Component: CSS
• Status: RESOLVED CONFIGURATION CHANGED

[Ryan Reno]

The static position of absolutely positioned children of multi-line flex containers will use the container's align-content to position the child when webkit.org/b/221472 is resolved. However, we will maintain our current behavior for the case of align-content: stretch. This is contrary to the spec which calls for a fallback to align-content: flex-start when the available space in the container is negative. (e.g. when the child is larger than the container).

This fallback behavior is ignored by all major engines and has been shipping with agreement for quite a while. Additionally, stretch is the normal, or default, behavior of align-content. A change in behavior here may have webcompat consequences. I raised an issue with the CSSWG to change the spec to match current browser behavior. Until that is resolved, this bug tracks the unspecified behavior we implement in WebKit for this one case.

CSSWG issue: https://github.com/w3c/csswg-drafts/issues/7596

[Radar WebKit Bug Importer]

<rdar://problem/98573100>

[Ryan Reno]

The CSSWG resolved this issue in today's call. https://github.com/w3c/csswg-drafts/issues/7596#issuecomment-1225952646

tl;dr the spec will tell engines to ignore align-content for abspos children.

[Ryan Reno]

Spec has changed.