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[css-scroll-snap-2] Resolve multiple scroll-start-targets by reverse DOM order #10929

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[css-scroll-snap-2] Resolve multiple scroll-start-targets by reverse DOM order #10929

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54 changes: 27 additions & 27 deletions css-scroll-snap-2/Overview.bs
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Original file line number Diff line number Diff line change
Expand Up @@ -137,31 +137,32 @@ The 'scroll-start-target' property {#scroll-start-target}
<h4 dfn export id="initial-scroll-target">
Initial scroll target</h4>

The [=initial scroll target=] of a <a>scroll container</a> |scrollcontainer|
An [=initial scroll target=] of a <a>scroll container</a> |scrollcontainer|
is an element or pseudo-element
whose 'scroll-start-target'property is non-''scroll-start-target/none''
and whose nearest <a>scroll container</a> is |scrollcontainer|.
When multiple such elements or pseudo-elements exist,
user-agents should select the one
which comes first in [=tree order=].
When no such element or pseudo-element exists,
|scrollcontainer|’s <a>initial scroll target</a> is null.

<div algorithm="determine the initial scroll position from an initial scroll target">
If the <a>initial scroll target</a> of a <a>scroll container</a> is not null,
it should be used to determine the <a>initial scroll position</a> of |scrollcontainer|
by running the following steps:

1. Let |target| be the <a>initial scroll target</a> for |scrollcontainer|.
1. Let |position| be the result of running the steps to
<a spec="cssom-view-1">determine the scroll-into-view position</a> of |target|
with <var ignore>behavior</var> set to "auto",
<var ignore>block</var> set to "start",
<var ignore>inline</var> set to "nearest",
and <var ignore>scrolling box</var> set to |scrollcontainer|.
1. Set |scrollcontainer|'s <a>initial scroll position</a> to |position|.
</div>

and whose nearest <a>scroll container</a> is |scrollcontainer|. |scrollcontainer|
may have more than one <a>initial scroll target</a>.

<h5 dfn id="determine-scroll-start-target-position">Determining initial scroll position from
scroll-start-target</h5>
To determine the <a>initial scroll position</a> of a <a>scroll container</a> |scrollcontainer| using its
<a>initial scroll target</a>s, user-agents should run the following steps:

1. Let <dfn>initial-scroll-target-list</dfn> be a list of the <a>initial scroll target</a>s of |scrollcontainer|,
sorted in reverse <a data-link-type="dfn" href="https://dom.spec.whatwg.org/#concept-tree-order" id="ref-for-concept-tree-order">tree order</a>.
1. For |target| in <a>initial-scroll-target-list</a>:
1. Let |position| be the result of running the steps to
<a spec="cssom-view-1">determine the scroll-into-view position</a> of |target|
with <var ignore>behavior</var> set to "auto",
<var ignore>block</var> set to "start",
<var ignore>inline</var> set to "nearest",
and <var ignore>scrolling box</var> set to |scrollcontainer|.
1. Set |scrollcontainer|'s <a>initial scroll position</a> to |position|.

NOTE: Sorting <a>initial-scroll-target-list</a> in reverse
<a data-link-type="dfn" href="https://dom.spec.whatwg.org/#concept-tree-order" id="ref-for-concept-tree-order">tree order</a>
is intended to prioritize having the first <a>initial scroll target</a> in tree order
scrolled into view.

<h4 id="scroll-start-target-propdef">scroll-start-target Property Definition</h4>

Expand Down Expand Up @@ -199,10 +200,9 @@ Post-first layout arrivals</h4>
a <a>scroll container's</a> [=initial scroll target=] might arrive
after that <a>scroll container</a> has been laid out.
If this happens,
user agents should still scroll to the [=initial scroll target=]
unless the user agent has reason to believe
the user is no longer interested
in scrolling to the <a>initial scroll position</a>.
user agents should still scroll to the <a>initial scroll position</a>
<a href="determine-scroll-start-target-position">determined</a> by 'scroll-start-target' unless the user agent has reason to believe
the user is no longer interested in scrolling to the <a>initial scroll position</a>.


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