[css-anchor-position] Does fallback affect the computed style?

[emilio]

https://drafts.csswg.org/css-anchor-position-1/#fallback-rule is pretty vague on how fallback applies.

Should the fallback be observable from getComputedStyle()? What about computedStyleMap?

Presumably insets/margins should since those return the used values from getComputedStyle, but others properties won't?

[xiaochengh]

I think these are already clear in the current specs.

https://drafts.csswg.org/css-anchor-position-1/#fallback-apply:

When an element uses a position fallback list, it selects one entry from the list as defined below, and applies those properties to itself as used values."

So they are applied at used value time (during layout), and do not affect the computed values.

Should the fallback be observable from getComputedStyle()?

Yes, because getComputedStyle() returns used values for some properties.

What about computedStyleMap?

No, because computedStyleMap holds computed values only.

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Note: this is just how it currently works, but ideally, we would still like fallback declarations to be applied at computed value time, so that smooth transitioning between fallback positions can be possible. See #8372

[emilio]

Ok, that matches my intuition on how it should be spec'd, great :)

I think I just didn't realize that was properly defined further down. Maybe https://drafts.csswg.org/css-anchor-position-1/#fallback-rule should somehow link to that section?

[xiaochengh]

I assume this issue is purely editorial then?

[emilio]

Yes

[tabatkins]

This should be well specified now.