Re: [csswg-drafts] [css-overflow-3] Does block-level box's margins contribute to scrollable overflow? (#8660)

> The spec is fine wrt. to this IMO. The margins aren't directly added to the scrollable overflow - rather the margins are affecting the inflow-bounds:
> 
> "Additional padding added to the end-side of the scrollable overflow rectangle as necessary to enable a scroll position that satisfies the requirements of place-content: end alignment."
I don't think it's well-defined what it means to `satisf[y] the requirements of place-content: end alignment`, though.  To the extent that it *is* well-defined, it seems the spec says to do nothing in this case.

The axis we're discussing here is the inline axis, which would correspond to the `justify-content` subproperty in this `align-content:end` expression.  And css-align-3 explicitly says:
And [the definition of justify-content](https://drafts.csswg.org/css-align-3/#distribution-block) says:
 justify-content Axis | **Does not apply to and has no effect on block containers**

(There's some nuance for scroll-container-specific behavior in [css-align-3 section 5.3](https://drafts.csswg.org/css-align-3/#overflow-scroll-position), but that still ties back to "the expected alignment of the alignment subject and alignment container", which in this case is "no effect".)

So  AFAICT `justify-content:end` is defined as **having no effect** on block containers, regardless of whether they're scrollable.

So we might need to rewrite what this `place-content` reliance is supposed to mean, or adjust css-align-3 section 5.3 to make it clearer what's supposed to happen w.r.t. the initial scroll position for containers-that-are-unaffected-by-justify-content.

> @dshin-moz - https://www.software.hixie.ch/utilities/js/live-dom-viewer/?saved=11469 Gecko is only doing the weird treatment in one axis as well.

Haven't looked closely at this yet, but if it's relevant, we haven't landed our changes for https://github.com/w3c/csswg-drafts/issues/129 yet (https://bugzilla.mozilla.org/show_bug.cgi?id=1768921 ).

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Received on Friday, 31 March 2023 17:08:58 UTC