Re: [csswg-drafts] Anchor positioning proposal comparison `[css-anchor-position]` (#9117)

> “Animations and transitions” — the current specs only allow transitions when changing the anchor inside the anchor()/anchor-size(), but not when swapping the values of the anchor-name (which could be more convenient for a lot of cases). A related issue: 

To phrase this a little more clearly for others, changing from `top: anchor(--foo)` to `top: anchor(--bar)` works (it's a computed-value change, and will trigger a transition) but using `top: anchor(--foo)` and then changing which element that refers to (by changing the `anchor-name` property on other elements) doesn't (it's a used-value change right now, only visible when the `anchor()` function finally resolves into a length, so it's too late for transitions. That is, the computed value of `anchor()` is the specified value, but the used value is the actual length it's specified to resolve to.

Fixing that is easy on the spec side (as outlined in #8181, it just requires resolving the anchor name into an element reference at computed-value time), but as Xiaocheng said it's harder in our impl right now (but possible).

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Received on Thursday, 27 July 2023 22:24:47 UTC