[csswg-drafts] [css-borders-4] Clarify the non-elliptical nature of `corner-shape: scoop` (#12620)

satgo1546 has just created a new issue for https://github.com/w3c/csswg-drafts:

== [css-borders-4] Clarify the non-elliptical nature of `corner-shape: scoop` ==
The `scoop` value for `corner-shape` is not an exact opposite of `round` — in fact, far from it.

<img width="1220" height="720" alt src="https://github.com/user-attachments/assets/8a465a0c-aefd-476c-b70b-cb8ef88585d3">

red: true circular arc\
blue: `superellipse(-1)` or `scoop` as defined per spec

The spec addresses this in a collapsed section "How does a superellipse work?":

> […] a *K* of -1 gives a nearly elliptical "scoop" that’s roughly the opposite of a *K* of 1, […]

Note the words 'roughly' and 'nearly'.

However, the definition of `scoop` seems to imply that it is elliptical.

> The corner shape is a concave quarter-ellipse. Equivalent to `superellipse(-1)`.

Figure 1 is also misleading in that the curve for K = -1 is drawn as a circluar arc symmetric to the case of K = 1.

> <img width="256" height="256" alt src="https://github.com/user-attachments/assets/35daa02e-01b5-4b9f-8cab-34d57a0d59c4">

I believe it should be clarified that the `scoop` shape is not a quarter-ellipse, and the effects of positive and negative values of K are asymmetric.

Incidentally, Chromium has implemented `superellipse(K)` with negative K values as the perfect opposite of those with positive K values, which is not compliant. I've created [an issue there](https://crbug.com/439718695), too.

Please view or discuss this issue at https://github.com/w3c/csswg-drafts/issues/12620 using your GitHub account


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Received on Tuesday, 19 August 2025 11:30:18 UTC