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[css-scroll-anchoring-1] Add more details to anchor node selection #3476

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[css-scroll-anchoring-1] Add more details to anchor node selection #3476

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82cba89
[css-scroll-anchoring-1] Fix link-defaults for content-area and css2 …
eqrion Jan 2, 2019
7adba8c
[css-scroll-anchoring-1] Make `position: sticky` an excluded subtree
eqrion Dec 18, 2018
3f7adf1
[css-scroll-anchoring-1] Add condition to not select scroll anchor wh…
eqrion Dec 18, 2018
c87b95b
[css-scroll-anchoring-1] Move and expand section on anchor node inval…
eqrion Jan 2, 2019
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26 changes: 19 additions & 7 deletions css-scroll-anchoring-1/Overview.bs
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Expand Up @@ -18,7 +18,9 @@ Abstract: This spec also proposes an API for web developers to opt-out of this b
</pre>

<pre class=link-defaults>
spec:css22;
spec:css-box-3; type:dfn; text:content area
spec:cssom-view-1; type:dfn; text:scrolling area
spec:css2;
type:property;
text:max-height
text:min-height
Expand Down Expand Up @@ -78,7 +80,9 @@ In some cases, a scrolling box may not select any anchor node.
1. If |S| is associated with an element
whose computed value of the 'overflow-anchor' property is ''overflow-anchor/none'',
then do not select an anchor node for |S|.
2. Otherwise, for each DOM child |N| of the element or document associated with |S|,
2. If |S| is not scrolled away from the origin of its <a>scrolling area</a> in its
<a>block flow direction</a>, then do not select an anchor node for |S|.
3. Otherwise, for each DOM child |N| of the element or document associated with |S|,
perform the <a>candidate examination algorithm</a> for |N| in |S|,
and terminate if it selects an anchor node.
</div>
Expand Down Expand Up @@ -110,17 +114,13 @@ In some cases, a scrolling box may not select any anchor node.
content to shift without triggering any scroll anchoring adjustment.
</div>

Conceptually, a new anchor node is computed for every scrolling box
whenever the scroll position of any scrolling box changes.
(As a performance optimization,
the implementation may wait until the anchor node is needed before computing it.)

<div algorithm>
A DOM node |N| is an <dfn>excluded subtree</dfn>
if it is an element and any of the following conditions holds:

* |N|’s computed value of the 'display' property is ''display/none''.
* |N|’s computed value of the 'position' property is ''position/fixed''.
* |N|’s computed value of the 'position' property is ''position/sticky''.
* |N|’s computed value of the 'position' property is ''position/absolute''
and |N|’s <a>containing block</a> is an ancestor of the scrolling box.
* |N|’s computed value of the 'overflow-anchor' property is ''overflow-anchor/none''.
Expand All @@ -147,6 +147,18 @@ the implementation may wait until the anchor node is needed before computing it.
or the bounding rect of its <a>line boxes</a> if |N| is a text node.
</div>

<h4 id='anchor-node-invalidation'>
Invalidation</h3>

An anchor node is considered valid for a <a>scrolling box</a> until any of the following occur:
* The scroll position of the <a>scrolling box</a> changes (excluding adjustments originating from scroll anchoring).
* A <a>suppression trigger</a> suppresses a scroll adjustment.
* The <a>anchor node</a> is removed from the DOM.

Once an anchor node has become invalid, the <a>anchor node selection algorithm</a> must be run again to compute the anchor node

As a performance optimization, implementations may wait until the <a>anchor node</a> is needed before computing it.

<h3 id="scroll-adjustment">
Scroll Adjustment</h3>

Expand Down