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Re: [csswg-drafts] [css-contain] Is it ok that contain:layout is a CB for fixpos/abspos descendants but doesn't establish a stacking context?

From: Daniel Holbert via GitHub <sysbot+gh@w3.org>
Date: Fri, 20 Jul 2018 21:49:01 +0000
To: public-css-archive@w3.org
Message-ID: <issue_comment.created-406735520-1532123340-sysbot+gh@w3.org>
RE how tied together they are:

Right now, the [CSS painting order algorithm](https://drafts.csswg.org/css2/zindex.html#painting-order) has three different mentions of a special category: `positioned descendants and descendants which actually create a new stacking context`.

Fun fact: up until now, this category has basically been 100% equivalent to "the set of all elements that establish a containing block for abs-pos descendants".  (Please correct me if I'm wrong, but I'm pretty sure these are 100% equivalent!)  However -- with the current contain:layout spec-text, these two categories will be slightly disjoint.  Specifically, `contain:layout` elements will be in the latter category (they establish a containing block) but they might not be in the former category (they're not necessarily positioned themselves, nor do they create a stacking context).

So I think the questions here are:
 - In the CSS Painting Order algorithm, would we want `contain:layout` elements to be included or excluded from the pieces about "positioned descendants and descendants which actually create a new stacking context"?  (And to what extent does this matter?)
 - Does this matter enough to create this new special-case (things which **are** abpsos containing blocks but **are not** themselves positioned nor do they form stacking contexts)?

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Received on Friday, 20 July 2018 21:49:08 UTC

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