[fxtf-drafts] [motion-1] anchor-position - which box? (#503)

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

== [motion-1] anchor-position - which box? ==
The [`anchor-position` property](https://drafts.fxtf.org/motion-1/#offset-anchor-property) says that percentages are relative to the width and height of "a box". The prose definition of the `<position>` value manually defines how to interpret a percentage, specifying that they're relative to "the content area". None of the examples have padding, border, or margin on the offset element, so it's impossible to tell what exactly is intended here, as all of the elements' boxes coincide.

Since 'offset-anchor' is clearly intending to match up with 'transform-origin' by default, I suspect we want to use the same box it does. I'm not sure whether we want to always use the *initial* value of [`transform-box`](https://drafts.csswg.org/css-transforms-1/#reference-box) or the *computed* value.

I suspect the best answer is the initial value (the "view box", aka border box for CSS). When you want to match the transform origin *exactly*, you can do that already with `auto`. I'm not sure what the use-cases would be to specify a *different* point than the transform origin that nevertheless requires using the *same box* as the transform origin. If we do realize we want to match this, we can always add a corresponding property with `none | auto | <'transform-box'>` as the value.

Please view or discuss this issue at https://github.com/w3c/fxtf-drafts/issues/503 using your GitHub account


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Received on Friday, 3 March 2023 20:33:03 UTC