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Re: [csswg-drafts] [css-multicol] Definition of adjacent spanners, when to create column boxes (#6265)

From: CSS Meeting Bot via GitHub <sysbot+gh@w3.org>
Date: Wed, 12 May 2021 16:14:19 +0000
To: public-css-archive@w3.org
Message-ID: <issue_comment.created-839909999-1620836057-sysbot+gh@w3.org>
The CSS Working Group just discussed `[css-multicol] Definition of adjacent spanners, when to create column boxes`, and agreed to the following:

* `RESOLVED: Confirm that abspos elemetns do not create column boxes and this adjacent spanners sep by abspos will collapse margins`

<details><summary>The full IRC log of that discussion</summary>
&lt;dael> Topic: [css-multicol] Definition of adjacent spanners, when to create column boxes<br>
&lt;dael> github: https://github.com/w3c/csswg-drafts/issues/6265<br>
&lt;dael> rachelandrew: Couple of linked issue with out of flow items<br>
&lt;dael> rachelandrew: I think example is straightforward. Got adjacent spanners that come directly after. margins collapse is in spec<br>
&lt;dael> rachelandrew: If you have abspos item inbetween which is taken out of flow we don't have interop. Gecko is not margin collapsing. Keeping abspos item separating. Blink and Safari do collapse<br>
&lt;dael> rachelandrew: Morton brought up b/c new fragementation engine doesn't<br>
&lt;dael> rachelandrew: What happens if we have out of flow item between 2 column spanners. Happy with margins not collapsing or want them to collapse<br>
&lt;iank_> yes<br>
&lt;dael> astearns: if you have non-spanning elements sep by out of flow do margins collapse?<br>
&lt;dael> rachelandrew: um...I'd have to test. Not sure<br>
&lt;dael> fantasai: They do collapse<br>
&lt;dael> rachelandrew: Cool<br>
&lt;dael> dholbert: I posted test case on GH showing they do in the simplified scenario<br>
&lt;dael> fantasai: I think this is a little...worth pointing out if you have abspos content contained by a block-level box and you remove the boxes it gets trapped and creates columns.<br>
&lt;dael> fantasai: If abspos is directly contained by multicol I don't see that is should cause creation of margin<br>
&lt;dael> rachelandrew: That's what I thought. It would mean Gecko changing what they're doing<br>
&lt;fantasai> s/and you remove the boxes/<br>
&lt;fantasai> s/and you remove the boxes//<br>
&lt;dael> astearns: fantasai you suggest in case where abspos is contianed by siblining it's different?<br>
&lt;TYLin> q+<br>
&lt;astearns> ack TYLin<br>
&lt;dael> fantasai: If there's an abspos position:releative element it creats column boxes and abspos can cause a height. But it's the block box causing the columns. When it's directly contained no reason to create columns and therefore not effect margins<br>
&lt;fantasai> s/abspos/abspos inside it/<br>
&lt;dael> TYLin: Reason why FF is not collapsing margin is b/c when it's out of flow it still leaves placeholder which triggers column box to be created so there is a gap between the adjacent<br>
&lt;dael> fantasai: But margin collapsing rules generally ignore abspos leements. So no reason why that should be happening<br>
&lt;dael> TYLin: Agree<br>
&lt;dael> dholbert: Create the column box to create placeholder. If say abspos placeholder don't get a box that would fix it<br>
&lt;dael> fantasai: placeholders only exist in tables.<br>
&lt;dael> dholbert: Yeah. Abspos elements don't cause creation of column box. I think that's what you're proposing.<br>
&lt;fantasai> s/tables/table box generation, as far as the specs are concerned. They're otherwise an implementation artifact/<br>
&lt;dael> astearns: Sounds like FF is willing to change<br>
&lt;dael> astearns: It was said Morton brought this up b/c new generation matched FF<br>
&lt;dael> rachelandrew: I don't think it was a concious choice but was impl details. I'm assuming they're happy to go back. We can ask<br>
&lt;dael> iank: I didn't get to talk with Morton before meeting. I think we'd be fine with that<br>
&lt;florian> s/Morton/Morten/<br>
&lt;dael> astearns: prop: Confirm that abspos eleemtns do not create column boxes and this adjacent spanners sep by abspos will collapse margins<br>
&lt;dael> fantasai: It hink it's no change<br>
&lt;dael> astearns: Clarifications and some tests, I suspect<br>
&lt;dael> fantasai: [missed] amrgin collapsing eslewehre might. Need tests<br>
&lt;dael> iank_: Don't know if that's correct about don't create column boxes. Might conflict with next issue<br>
&lt;dael> iank_: And that issue is basically does column balancing apply when you've only got abspos in multicol<br>
&lt;dael> fantasai: Not in conflict b/c columns not being created by abspos in the next issue. Box with position:relative creates it. It might be 0 height and can't see, but it's causing creation of column row<br>
&lt;dael> iank_: I guess this sort of gets at...need to think about it<br>
&lt;fantasai> s/[missed]/if we call this out in the spec, that implies that/<br>
&lt;dael> astearns: Why don't we resolve adjacent spanners sep by abspos elements will collapse margins<br>
&lt;fantasai> s/Need tests/Need tests, but no change to spec/<br>
&lt;dael> astearns: Abspos elements not creating column boxes is probably implied. But we can go with just margin collapsing for now<br>
&lt;dael> iank_: Re-read next, I was wrong<br>
&lt;dael> astearns: Back to orginal proposal. "Confirm that abspos elemetns do not create column boxes and this adjacent spanners sep by abspos will collapse margins"<br>
&lt;dael> RESOLVED: Confirm that abspos elemetns do not create column boxes and this adjacent spanners sep by abspos will collapse margins<br>
</details>


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