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[css-anchor-position-1] Depluralize anchors-* in 'position-visibility' and only check default anchor #10201 #13768

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[css-anchor-position-1] Depluralize anchors-* in 'position-visibility' and only check default anchor #10201 #13768

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31 changes: 15 additions & 16 deletions css-anchor-position-1/Overview.bs
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Original file line number Diff line number Diff line change
Expand Up @@ -2219,8 +2219,8 @@ Conditional Hiding: the 'position-visibility' property {#position-visibility}

<pre class=propdef>
Name: position-visibility
Value: always | [ anchors-valid || anchors-visible || no-overflow ]
Initial: anchors-visible
Value: always | [ anchor-valid || anchor-visible || no-overflow ]
Initial: anchor-visible
Applies to: [=absolutely positioned boxes=]
Percentages: n/a
Inherited: no
Expand All @@ -2239,23 +2239,14 @@ depending on some commonly needed layout conditions.
(The box is displayed without regard for its anchors
or its overflowing status.)

: <dfn>anchors-valid</dfn>
: <dfn>anchor-valid</dfn>
::
If any of the box's [=required anchor references=]
do not resolve to a [=target anchor element=],
If the box references the [=default anchor box=]
(e.g. using 'position-area', 'anchor()' or 'anchor-size()' functions, or ''anchor-center''),
but the [=default anchor box=] cannot be resolved,
the box's 'visibility' property computes to ''force-hidden''.

Issue: What is a <dfn dfn for>required anchor reference</dfn>?
''anchor()'' functions that don't have a fallback value;
the default anchor *sometimes*?
Need more detail here.

Issue: <em>Any</em> anchors are missing,
or <em>all</em> anchors are missing?
I can see use-cases for either, potentially.
Do we want to make a decision here, or make it controllable somehow?

: <dfn>anchors-visible</dfn>
: <dfn>anchor-visible</dfn>
::
If the box has a [=default anchor box=]
but that [=anchor box=] is [=invisible=] or [=clipped by intervening boxes=],
Expand Down Expand Up @@ -2704,6 +2695,14 @@ No Privacy issues have been raised against this document.
Changes {#changes}
=======

Significant changes since the <a href="https://www.w3.org/TR/2026/WD-css-anchor-position-1-20260327/">27 March 2026 Working Draft</a>:
* Defined ''position-visibility/anchor-valid'' to (like ''position-visibility/anchor-valid'') only check the [=default anchor box=].
(<a href="https://github.com/w3c/csswg-drafts/issues/10201">Issue 10201</a>)
* Renamed <css>anchors-valid</css> and <css>anchors-visible</css>
to ''position-visibility/anchor-valid'' and ''position-visibility/anchor-visible''
since they only reference the [=default anchor box=].
(<a href="https://github.com/w3c/csswg-drafts/issues/10201">Issue 10201</a>)

Significant changes since the <a href="https://www.w3.org/TR/2026/WD-css-anchor-position-1-20260130/">30 January 2026 Working Draft</a>:
* Added ''position-area/match-parent'' value to 'position-area'.
(<a href="https://github.com/w3c/csswg-drafts/issues/8913">Issue 8913</a>)
Expand Down