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Merged
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Jul 2, 2015
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Florian/contain and clip #33

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4a71f42
[css-overflow] Add computed value logic for overflow and contain: paint
frivoal Jul 1, 2015
a83fcc9
[css-containment] Express paint containment in terms of overflow:clip
frivoal Jul 1, 2015
43a8b06
[css-containment] Improve phrasing
frivoal Jul 1, 2015
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11 changes: 8 additions & 3 deletions css-containment/Overview.bs
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Expand Up @@ -197,8 +197,12 @@ Paint Containment</h3>

Giving an element <dfn export>paint containment</dfn> has the following effects:

1. The contents of the element must be clipped to the element's content box.
This includes both the paint of the descendants and their geometry (similar to overflow).
1. As specified in [[!CSS-OVERFLOW-3]],
the computed value the 'overflow-x' and 'overflow-y' is changed to ''overflow/clip''
if it would otherwise have been ''overflow/visible''.
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@tabatkins tabatkins Jul 1, 2015

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I prefer "If the computed value of overflow-x or overflow-y would otherwise have been 'visible', it must instead compute to 'clip'. [[!CSS-OVERFLOW-3]]"

<span class=note>This means that regardless of the specified value of 'overflow',
the contents of the element is clipped to the element's content box,
including both the paint of the descendants and their geometry</span>
2. The element must act as a containing block for absolutely positioned and fixed positioned descendants.
3. The element must be a <a>formatting context</a>.

Expand All @@ -208,7 +212,8 @@ Paint Containment</h3>
the UA can directly skip trying to paint its contents,
as they're guaranteed to be off-screen/obscured as well.

2. If the containing element is ''overflow:visible'',
2. If the containing element would have been ''overflow:visible'',
it becomes ''overflow:clip'' and
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@tabatkins tabatkins Jul 1, 2015

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This line sounds like normative instructions; I'd prefer a parenthetical like (but is now overflow:clip due to paint containment), or something more direct, like "If the containing element's overflow has been changed to 'clip' (because it was originally visible), ..."

the UA can reserve "canvas" space for the element exactly the element's size.
(In similar, scrollable, situations, like ''overflow: hidden'',
it's possible to scroll to the currently-clipped content,
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11 changes: 11 additions & 0 deletions css-overflow/Overview.bs
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Expand Up @@ -28,6 +28,8 @@ type: dfn; spec:css-multicol-1; text:overflow column
<pre class="anchors">
url: http://www.w3.org/TR/2008/CR-css3-marquee-20081205/#the-overflow-style; type: property; text: overflow-style;
url: http://dev.w3.org/csswg/selectors-3/#subject; type: dfn; text: subject;
url: http://dev.w3.org/csswg/css-containment/#propdef-contain; type: property; text: contain
url: http://dev.w3.org/csswg/css-containment/#paint-containment; type: dfn; text: paint containment
</pre>
<style>
table.source-demo-pair {
Expand Down Expand Up @@ -420,6 +422,15 @@ Introduction</h2>
then computed values are the cascaded values
with ''overflow/visible'' changed to ''overflow/auto''.
</li>
<li>
Otherwise, if both cascaded values are ''overflow/visible''
and the computed value of 'contain' is
one that activates <a>paint containment</a>
(e.g. ''contain:strict''
or ''contain: paint''
or ''contain: layout paint''…),
then the computed values of both 'overflow-x' and 'overflow-y'
are changed to ''overflow/clip''.</li>
<li>
Otherwise, the computed values are as specified.
</li>
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