[css-images-4][css-shapes-1] Elliptical shape defined with a single <length-percentage>

[cdoublev]

In CSS Images 3, a non-normative note restricts the syntax of radial-gradient(): ellipse can be used only with a single <radial-extent> keyword or two <length-percentage>s. In prose, this restriction is not very clear: one may think it could use a single <length>, but browsers actually do not allow this, and implements the syntax defined in the non-normative note.

CSS Images 4 now seems to allow using two <radial-extent> keywords or a single <length-percentage> for an elliptical radial-gradient() or for ellipse() (CSS Shapes).

Is this an oversight? If so, I suggest to hardcode these restrictions in the syntax:

<circle()> = circle( <radial-size>? [ at <position> ]?)
<ellipse()> = ellipse( [ <radial-size>{2} ]? [ at <position> ]?)>
<radial-gradient-syntax> = <radial-shape>? [ at <position> ]? , <color-stop-list>
<radial-shape> = [ circle || <radial-size> ] | [ ellipse || <radial-size>{2} ]
<radial-size> = <radial-extent> | <length-percentage [0,∞]>

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If this is deliberate, can you please clarify how to serialize ellipse 1px, assuming the second component value should default to farthest-corner? Should it be ellipse 1px or 1px farthest-corner?

Specified	Serialized
farthest-corner	omitted
farthest-corner farthest-corner	omitted
closest-corner	closest-corner
closest-corner closest-corner	closest-corner closest-corner
closest-corner farthest-corner	closest-corner
circle	circle
circle 1px	1px
circle closest-corner	circle closest-corner
circle farthest-corner	circle
ellipse	omitted
ellipse 1px	?
ellipse 1px 1px	1px 1px

^{Edit: updated the default value of the second component value, which I think should be farthest-corner instead of the first component.}

[cdoublev]

Closing in favor of #10812.