[css-display-4] Relax list-item display type limitations

[EllyLoel]

Using list-style-position: outside; with ordered lists commonly leads to issues where the ::marker overflows the edge of the viewport because the size of the ::marker is not always the same.

To fix this you can use list-style-position: inside; but then the alignment of all of the list's ::markers is ruined. So to fix the alignment the first thing that came to my mind (and others) is to use subgrid like this:

:is(ul, ol) {
	padding: 0;
	list-style-position: inside;
	display: grid;
	grid-template-columns: min-content 1fr;

	> li {
		align-items: baseline;
		grid-column: 1 / -1;
		display: block grid list-item;
		grid-template-columns: subgrid;

		> * {
			grid-column: 2 / -1;
		}
	}
}

But unfortunately according to the spec this isn't currently allowed:

Note: In this level, as restricted in the grammar, list-items are limited to the Flow Layout display types (block/inline/run-in with flow/flow-root inner types). This restriction may be relaxed in a future level of this module.
— The note from 2.3. Generating Marker Boxes: the list-item keyword in CSS Display Module Level 3

This restriction means using display: block grid list-item; to fix the alignment issue is not allowed. So I would love to see the list-item display type limitations relaxed so this is possible!

[Loirooriol]

list-style-position: outside isn't really defined for block containers (other than some handwavey nonsense from CSS2).
It's even less clear how it would behave in flex or grid layout.