I wonder if it's possible do reification generically for a subset of properties so that we don't have to write so much spec text.

For example, could we say that if a property only takes identifiers, then its specified value reifies as a CSSKeywordValue. Another thing we could do is if a property's computed value is "as specified", then the computed reification is the same as specified reification etc.

On the other hand, we'll probably need to specify a list of all the supported properties anyway, and copy & pasting for those simple cases doesn't add that much time.