[csswg-drafts] [css-anchor-position] Details on "anchors-valid" (#10201)

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

== [css-anchor-position] Details on "anchors-valid" ==
The "no-overflow" and "anchors-visible" values of [`position-visibility`](https://drafts.csswg.org/css-anchor-position/#position-visibility) were straightforward to define. The "anchors-valid" value, tho, ended up with several important questions to answer that I'm not sure about.

1. What exactly is a "required anchor reference"? 
    * `top: anchor(--foo bottom);` is clearly one. 
    * Is `top: anchor(--foo bottom, anchor(--bar bottom));` one (on --foo) or two (on --foo and --bar)? Or is it an "or" relationship - if *either* --foo or --bar is a valid reference, it works?
    * When exactly is the default anchor element a required reference? We can't just rely on `anchor(bottom)` references, as several other features reference the default anchor. Note that the initial value isn't "none", it's "implicit", so technically we're *always* **attempting** to reference a default anchor. Even if there isn't a single `anchor(bottom)` function on the element, the author could conceiveably be depending on the implicit anchor existing for its other effects.
    * How does fallback affect this? In general, `position-visibility` runs "after" fallback selection, so I presume we'd rely on the set of properties being used by the active fallback, and references in other fallbacks won't matter.

2. Do we want it to make the element invisible if *any* required references are invalid, or if *all* of them are? Is this something that needs to be controllable? (I'm inclined to say "any", since if you don't care about a given reference not resolving, you can always just give it a fallback value. Except for the default anchor...)

Please view or discuss this issue at https://github.com/w3c/csswg-drafts/issues/10201 using your GitHub account


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Received on Thursday, 11 April 2024 22:01:34 UTC