Contact emailsmsten...@chromium.org

ExplainerNone

Specificationhttps://drafts.csswg.org/css-anchor-position-1/#scroll

Summary

Add support for the concept of "remembered scroll offset" - see
https://drafts.csswg.org/css-anchor-position-1/#scroll When a positioned
element has a default anchor, and is tethered to this anchor at one edge,
and against the original containing block at the other edge, the scroll
offset will be taken into account when it comes to sizing the element. This
way a developer can use all visible space (using `position-area`) for the
anchored element when the document is scrolled at a given scroll offset. In
order to avoid layout (resizing the element) every time the document is
scrolled (which is undesired behavior, and also bad for performance), what
will be used is a so-called "remembered scroll offset", rather than always
using the current scroll offset. The remembered scroll offset is updated at
a so-called "anchor recalculation point", which is either: - When the
positioned element is initially displayed - When a different position
option (`position-try-fallbacks`) is chosen


Blink componentBlink>Layout
<https://issues.chromium.org/issues?q=customfield1222907:%22Blink%3ELayout%22>

TAG reviewNone

TAG review statusPending

Risks


Interoperability and Compatibility

Anchor positioning isn't shipping in any other engine yet.


*Gecko*: Positive (https://github.com/mozilla/standards-positions/issues/794)
Anchor positioning not implemented in Firefox.

*WebKit*: Support (https://github.com/WebKit/standards-positions/issues/167)
Anchor positioning not implemented in Safari.

*Web developers*: No signals

*Other signals*:

WebView application risks

Does this intent deprecate or change behavior of existing APIs, such that
it has potentially high risk for Android WebView-based applications?

None


Debuggability

None


Will this feature be supported on all six Blink platforms (Windows, Mac,
Linux, ChromeOS, Android, and Android WebView)?No

Is this feature fully tested by web-platform-tests
<https://chromium.googlesource.com/chromium/src/+/main/docs/testing/web_platform_tests.md>
?Yes

https://wpt.fyi/results/css/css-anchor-position?label=master&label=experimental&aligned
https://wpt.fyi/results/css/css-anchor-position/position-area-scrolling-005.html?label=master&label=experimental&aligned


Flag name on about://flags

Finch feature nameCSSAnchorRememberedScrollOffset

Requires code in //chrome?False

Tracking bughttps://issues.chromium.org/issues/373874012

Estimated milestones
Shipping on desktop 135
Shipping on Android 135
Shipping on WebView 135

Anticipated spec changes

Open questions about a feature may be a source of future web compat or
interop issues. Please list open issues (e.g. links to known github issues
in the project for the feature specification) whose resolution may
introduce web compat/interop risk (e.g., changing to naming or structure of
the API in a non-backward-compatible way).
None

Link to entry on the Chrome Platform Status
https://chromestatus.com/feature/4710507824807936?gate=5315183922380800

Links to previous Intent discussionsIntent to Prototype:
https://groups.google.com/a/chromium.org/d/msgid/blink-dev/CAKWZFm5%3D2_bAxBDiD%3DzDaxbZOx7SZiZvEc5tmwCkUfTxevkphw%40mail.gmail.com


This intent message was generated by Chrome Platform Status
<https://chromestatus.com/>.

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