[motion-1] Issues with offset-path examples in the spec usage of 'margin-box'

[weinig]

The current Motion Path spec defines offset-path as:

none | <ray()> | <path()> | <url> | [ <basic-shape> && <coord-box>? ] | <coord-box>

https://drafts.fxtf.org/motion-1/#offset-path-property

The current definition of <coord-box> in css-box-4 is:

<coord-box> = content-box | padding-box | border-box | fill-box | stroke-box | view-box

https://drafts.csswg.org/css-box-4/#typedef-coord-box

However, a few examples (see https://drafts.fxtf.org/motion-1/#example-shape and https://drafts.fxtf.org/motion-1/#example-coord) in the Motion Path spec use margin-box, which is not one of the valid <coord-box> values.

Is it possible that in the past <coord-box> did include margin-box?

The CSS Masking spec defines a <geometry-box> production that is likely what is wanted here - https://www.w3.org/TR/css-masking-1/#typedef-geometry-box (especially interesting since it used for the clip-path property).

Perhaps moving the definition of <geometry-box> to CSS Box would be a good idea?

[nt1m]

@tabatkins Can you please take a look?