[css-sizing] Clarify contain-intrinsic-size:none vs 0

[Loirooriol]

From https://drafts.csswg.org/css-contain-2/#containment-size

The intrinsic sizes of the size containment box are determined as if the element had no content, following the same logic as when sizing as if empty.

From https://drafts.csswg.org/css-sizing-4/#explicit-intrinsic-inner-size

If an element has an explicit intrinsic inner size in an axis, then after laying out the element as normal for size containment, the size of the contents in that axis are instead treated as being the explicit intrinsic inner size instead of what was calculated in layout, and layout is performed again if necessary.

I don't really get the difference between sizing as there was no content, vs sizing as if the contents had a size of 0.

This case shows a difference in Blink:

<img src="image" style="border: solid; contain: inline-size; contain-intrinsic-width: none">
<img src="image" style="border: solid; contain: inline-size; contain-intrinsic-width: 0">

The 1st image has its natural width, the 2nd one is 0px wide. Not sure if this is correct.

[Loirooriol]

I guess contain-intrinsic-size: none may produce contents with a size greater than 0 due to gap, grid-template, ... but contain-intrinsic-size: 0 disregards all of that and 0 is the final content size? See #7520

[Loirooriol]

In #7520 (comment) Tab confirmed that the difference is that none may result in an intrinsic size greater than 0 due to other properties, while 0 disregards that. I think the spec should have a note or example.