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Re: [csswg-drafts] [css-display] Unclear definition of "formatting context" (#5105)

From: Oriol Brufau via GitHub <sysbot+gh@w3.org>
Date: Fri, 29 May 2020 17:43:22 +0000
To: public-css-archive@w3.org
Message-ID: <issue_comment.created-636099610-1590774201-sysbot+gh@w3.org>
1. Are additional boxes always nested in the principal box?

I think this is currently the case, yes.

> the principal box could be defined as the "outermost" box generated by the element in the box tree

Seems reasonable to me.

2. What does "continue" a formatting context mean?

It means that the box doesn't establish an independent formatting context, so its children will participate in the parent formatting context.

> Assuming there are no out-of-flow boxes, i.e. no floating boxes and no positioned boxes, what is the difference between creating a new independent FC and "continuing" the parent FC?

Well, for example margin collapse only happens in the same BFC. See the difderences in

<div><p>The &lt;div&gt; continues the BFC</p></div>
<div><p>The &lt;div&gt; continues the BFC</p></div>
<div style="display: flow-root"><p>The &lt;div&gt; establishes an independent BFC</p></div>
<div style="display: flow-root"><p>The &lt;div&gt; establishes an independent BFC</p></div>

3. How can two formatting contexts "co-exist"?

Well, that's because block and inline layout are two sides of the same coin (flow layout). So yes, you can consider flow layout to be a superset of block layout and inline layout.
Though I'm actually not pleased by this FC coexistence, I think that element-generated block containers should either continue their parent BFC or establish an independent BFC, but never an IFC. IFC should only be established by anonymous block containers IMO.

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Received on Friday, 29 May 2020 17:43:24 UTC

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