TabAtkins: I raised https://github.com/w3c/csswg-drafts/pull/7631 — though in general I don’t know what the criteria are for graduating a feature from a higher-level CSS spec version to a lower-level version

Also I reckon that at https://github.com/w3c/csswg-drafts/pull/7631/files#diff-085d78c8df023b773f3d83752e37b42504653aa890a136287411337bd835a97cL98 I didn’t get the syntax update done right — but I basically didn’t know enough to figure out how to resolve the discrepancy between the (more-complete) syntax that the Level 2 spec says is allowed, and the syntax that the Level 3 spec provides (which seems like it must be an unintentionally incomplete monkey patching…)