[csswg-drafts] [css-anchor-position-1] Clarification on resize observer timing steps (#12653)

vmpstr has just created a new issue for https://github.com/w3c/csswg-drafts:

== [css-anchor-position-1] Clarification on resize observer timing steps ==
In [spec](https://drafts.csswg.org/css-anchor-position-1/#fallback-apply) under Resize Observer steps, it says:

> At the time that [ResizeObserver](https://drafts.csswg.org/resize-observer-1/#resizeobserver) events are determined and delivered:

> If a box el is [absolutely positioned](https://drafts.csswg.org/css-position-3/#absolute-position), set its last successful position option to the set of [accepted @position-try properties](https://drafts.csswg.org/css-anchor-position-1/#accepted-position-try-properties) (and values) that it’s currently using.
> Otherwise, if el has a [last successful position option](https://drafts.csswg.org/css-anchor-position-1/#last-successful-position-option) and if any of the following are true of it, remove its last successful position option:
> - el is not [absolutely positioned](https://drafts.csswg.org/css-position-3/#absolute-position)
> - el’s computed value for [position-try-fallbacks](https://drafts.csswg.org/css-anchor-position-1/#propdef-position-try-fallbacks) has changed
> - Any of the [@position-try](https://drafts.csswg.org/css-anchor-position-1/#at-ruledef-position-try) rules referenced by el’s [position-try-fallbacks](https://drafts.csswg.org/css-anchor-position-1/#propdef-position-try-fallbacks) have been added, removed, or mutated.

I might be parsing this wrong, but this sounds like the following:
> if box el is abspos, do X
> otherwise do Y if any of the following hold:
> - box el is not abspos
> - [...]

which is equivalent to
> if box el is abspos do X, otherwise do Y

@tabatkins 

Please view or discuss this issue at https://github.com/w3c/csswg-drafts/issues/12653 using your GitHub account


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Received on Tuesday, 26 August 2025 00:56:49 UTC