[css-backgrounds][css-display][css-box] anchoring terminology for the border box taking corner shape into account.

[frivoal]

As a baby step towards defining hit testing that would be useful in other places as well, a css spec should define some anchoring terminology for the area encompassed by the border of an element, taking corner shaping (by border-radius and possible future properties) into account.

Quite possibly the term border edge is the one I'm after, but it is defined in CSS2.1 without mentioning border-radius, then effectively monkey-patched in CSS Backgrounds 3 §5.1 to say that it is affected by border radius. That spec should probably provide an updating definition of border edge that states explicitly states it takes corner shaping into account(corner shaping should probably be an anchor term as well), and then let border-radius state how does the corner shaping.

While we're at it, we should also clarify whether the border box takes corner shaping into account.

This would have been useful at least in in https://drafts.csswg.org/css-ui-3/#cursor, and in https://wicg.github.io/spatial-navigation/#heuristics

[frivoal]

Another spec where having a word for the explicitly shaped border / padding box is css-contain (see #2223).

I suggest that we:

• define corner shaping as an anchor term
• either:
  • have an updated definition of [border | padding] [box | edge] in a Level 3 spec that explicitly says that these terms always takes corner shaping into account
  • define new anchor terms for shaped [border | padding] [box | edge]

[css-meeting-bot]

The Working Group just discussed Missing box termonology, and agreed to the following resolutions:

• RESOLVED: Add the definition of the border shape edge to Borders and Backgrounds L3

The full IRC log of that discussion

<dael> Topic: Missing box termonology
<jihye> https://github.com//issues/2324
<dael> github: https://github.com//issues/2324
<dael> florian: background 3 says border radius changes border edge. If you link to border edge it doesn't say if it effects it. The spec that does talks about border edge but not the other varius boxes. It makes it really awk to refer to in other specs. If we can define the border edge in level 3
<dael> TabAtkins: I like shaped border edge to refer to it.
<dael> florian: And we can add all the thigns that can be shaped.
<dael> TabAtkins: WE wanted to refer to the things outside.
<dael> florian: If it effects hit testing it should be there.
<dael> iank_: clip-path yes, but I don't believe share-outside
<dael> florian: Editors will do it? I think it's border and backgrounds L3
<dael> TabAtkins: Sure. Seems fine.
<dael> astearns: Since it's just missing testing to go to rec....it's just a term. As long as you don't open hit testing in backgrounds and border I'll be happy.
<dael> Rossen: prop: Add the definition of the border shape edge to Borders and Backgrounds L3
<dael> RESOLVED: Add the definition of the border shape edge to Borders and Backgrounds L3