Should will-change: contain trigger CSS stacking context?

[smfr]

If contain:paint triggers creation of CSS stacking context, should will-change: contain trigger stacking context?

[dbaron]

I think the spec is pretty clear already:

If any non-initial value of a property would create a stacking context on the element, specifying that property in will-change must create a stacking context on the element.

[dbaron]

My big test says that Firefox and Chrome both create a stacking context for will-change: contain and it says that Safari doesn't support contain. Firefox also makes it a containing block for absolutely- and fixed-positioned elements, and I recently fixed Chrome to do the same (but it hasn't reached stable yet).

Note that the two paragraphs in the spec immediately after the one quoted above are:

If any non-initial value of a property would cause the element to generate a containing block for absolutely positioned elements, specifying that property in will-change must cause the element to generate a containing block for absolutely positioned elements.

If any non-initial value of a property would cause the element to generate a containing block for fixed positioned elements, specifying that property in will-change must cause the element to generate a containing block for fixed positioned elements.

[Loirooriol]

Previous discussion in #4612