Re: [csswg-drafts] [css-overflow] spec text for scrollable end-edge padding needs clarification (#6315)

I think my intuition for the expected behavior here is:
 - If there is overflow, then the scrolled box (the inner piece) is intrinsically sized to the content; it sizes as if it were a an `auto`-sized element with the contents that it's been given (except that percentages resolve against the size of the outer scrolled box, for example).
 - This intrinsically-sized-box gives us a content box (or an analog of a content-box) for the inner scrolled frame's contents, basically.
 - ...but, the thing that we want to be scrollable is the padding box, in general -- not the content-box (with the exception ofinline-end padding on scrollable blocks, for historical reasons; let's forget about that for the moment).
 - So: we should inflate this scrolled-frame-"content box" by the scrollframe's padding, and we contribute that to the scrollable area.

Importantly, this box (the one that we inflate by the padding) does *not* include the final relative positions of relatively-positioned children, nor does it include the boxes of distant overflowing grandchildren, or out-of-flow content.  Those things all do individually contribute to the scrollable area, but they **don't contribute to the box that we add the padding onto, when we determine how the padding influences the scrollable area**.

Does this make sense?  And does this actually match what the spec says right now? (It doesn't seem to clearly match the spec by my reading, at least.)   I think it does at least match (or roughly match) what Chromium and WebKit actually do, and it does match what Gecko will soon do as of https://bugzilla.mozilla.org/show_bug.cgi?id=1712875.

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Received on Wednesday, 26 May 2021 23:43:51 UTC