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Re: [csswg-drafts] [css-sizing-4] Should we mention aspect-ratio in margin collapsing? (#5328)

From: Tab Atkins Jr. via GitHub <sysbot+gh@w3.org>
Date: Tue, 06 Oct 2020 00:13:27 +0000
To: public-css-archive@w3.org
Message-ID: <issue_comment.created-703955011-1601943205-sysbot+gh@w3.org>
So for now we've committed the following:
> For the purpose of margin collapsing ([[css2#collapsing-margins]]),
> if the [=block axis=] is the [=ratio-dependent axis=],
> it is not considered to have a [=computed value|computed=] 'block-size' of ''height/auto''.

This communicates that a non-zero height caused by aspect-ratio definitely inhibits margin-collapse (as per the resolution above), but it also implies that aspect-ratio inhibits margin-collapse in all cases, even if the resulting height ends up being zero. This matches Firefox, but doesn't match Chrome currently. (Don't know about WebKit.)  It seems like adjusting Chrome to pay attention to aspect-ratio is a smaller task than adjusting Firefox to care about used values when doing margin-collapsing, so hopefully this is ok? Overall this is a corner-case anyway; the only time an ar-having box would get a zero height is if either the a-r is 0/X (weird) or is zero-width (rare).

There's a follow-up CSS2 issue about non-interop on collapsing margins at https://github.com/w3c/csswg-drafts/issues/5571

Let us know if this seems adequate to close the issue, or if further edits are wanted.

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