Conformance of revisions of levels of CSS #2587
Description
From CSS2§3, Conformance:
The validity of a style sheet depends on the level of CSS used for the style sheet. All valid CSS1 style sheets are valid CSS 2.1 style sheets, but some changes from CSS1 mean that a few CSS1 style sheets will have slightly different semantics in CSS 2.1. Some features in CSS2 are not part of CSS 2.1, so not all CSS2 style sheets are valid CSS 2.1 style sheets.
Do we really want to consider conformance of CSS2 as opposed to CSS 2.1 (and CSS 2.2)? Surely the only thing that really makes sense is conformance to "level 1" or "level 2" (because even "level 3" doesn't really make sense given it doesn't exist as a whole)?