1256438 - [flexbox] Implement Flex Item Baseline Content-Alignment

Status: NEW

(Core :: Layout, defect, P3)

Description

[Mats Palmgren (inactive)]

https://drafts.csswg.org/css-align-3/#baseline-align-content
"Baseline Content-Alignment
Flex Items:
    A flex item participates in first (last) baseline content-alignment in its flex line if its computed align-content is baseline (last-baseline), its inline axis is parallel to the main axis, and its computed align-self is stretch or self-start (self-end). For this purpose, the start, end, flex-start, and flex-end values of align-self are treated as either self-start or self-end, whichever they end up equivalent to."

I see that we have some kind of baseline alignment in the Flexbox code
but it appears to be for align/justify-self on Flex items, not align-/
justify-content on Flex items.

(the corresponding bug for Grid items is bug 1256429)