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Re: [css-containment][css-regions] how does containement and regions interact

From: Tab Atkins Jr. <jackalmage@gmail.com>
Date: Wed, 1 Jul 2015 11:22:34 -0700
Message-ID: <CAAWBYDAXtLQH9XtzYMEQOtNfg58OaFujzw8ihwotv=iuxA3e-w@mail.gmail.com>
To: Florian Rivoal <florian@rivoal.net>
Cc: www-style list <www-style@w3.org>
On Wed, Jul 1, 2015 at 8:08 AM, Florian Rivoal <florian@rivoal.net> wrote:
> The current definition of the 'contain' property doesn't work well
> with regions. flow-from and flow-into are scoped to the contain:style
> container, but that's not enough, and regions make contain:layout
> ineffective when used without contain:style.
>
> <article>
>   <div id=container>
>     <p>Lorem ipsum dolor sit amet...
>   </div>
>   <div id=container>
>     <div>...<table>...<tr>...<td>.../* arbitary nesting */
>        <p>Aenean vestibulum, dui eu bibendum sagittis...
>     </td>...</tr>...</table>...</div>
>   </div>
>   <p>Sed semper vehicula nisl ac dignissim...
> </article>
>
> <style>
> container {
>   contain:layout;
>   height: 100px;
>   width: 100px;
> }
> p { flow-into: my-flow; }
> p { flow-from: my-flow; }
> </style>
>
> You can't know what the content of the second or third <p>
> is going to be (and therefore you cannot lay them out)
> without first laying out the content of the preceding
> container. Which also means you cannot figure out the
> height of <article>, without doing a full layout of all
> its children, despite the presence of contain:layout on
> some of them.
>
> In the best case, that means that UAs cannot do the type of
> optimizations you'd expect from contain:layout if regions
> are involved, and in the worst case, that means UAs can
> never to the type of optimization you'd expect from
> contain:layout because regions *might* be involved, and
> it's too hard to figure out if they actually are.
>
> I see 2 ways out of that:
>
> 1) merge layout and style containment
>
> 2) add a region-specific rule to layout containment in addition
> to those in style containment. Here's one that should work:
>
>   The first (if any) region in a region chain that is either
>   a contain:layout element itself or the descendant of one is
>   treated as if it was the last region in the chain, and gets
>   all the remaining content in the associated named flow.
>   Subsequent regions in the chain do not receive any content
>   from the named flow.
>
> You'll still need to walk the through the preceding regions
> in a region chain before you can layout the next one, but
> if any of them is in a contain:layout element, you don't need
> to lay it out before you can continue.
>
> Actually, we need to reword that so that if several regions
> of the same chain are descendants of the same contain:layout
> element, it's the last of one rather than the first, that should
> behave as the last one in the chain. But that's hard to phase well,
> so it's probably easier to understand my point with the definition
> above, even if we need to tweak it before putting it in the spec.

I'm fine with layout containment also breaking region chains.

~TJ
Received on Wednesday, 1 July 2015 18:23:20 UTC

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