https://drafts.csswg.org/css-will-change/#valdef-will-change-custom-ident has phrasing like (the parts between brackets change in the various related clauses):

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].

I think this use of any is ambiguous: if some but not all of the non-initial values of that property would do the thing mentioned, are we in the must case or not?

I suggest rephrasing to either:

• if all values other than the initial value of a property would…
• if at least one of the values other than the initial value of a property would…