[css-cascade] [css-properties-and-values] [cssom] Define new constants for the new at rules?

[emilio]

Much like e.g., https://drafts.csswg.org/css-fonts/#om-fontfeaturevalues @property and @layer should probably define which constants do they return for CssRule.type?

I know it's deprecated etc, but we need to return something.

[tabatkins]

Already defined in your own spec, Emilio ^_^ https://drafts.csswg.org/cssom-1/#dom-cssrule-type All at-rules defined after @Viewport just return 0 for that attribute (and nothing after @namespace should have a constant, or else we should be inlining those constants for 11-14 into CSSOM as well).

Also documented on https://wiki.csswg.org/spec/cssom-constants

[emilio]

Whoopsies, I did recall some discussion about this lol.