[cssom][css-transforms] Serializing of functions

[annevk]

https://drafts.csswg.org/cssom/#serializing-css-values does not appear to describe how functions, such as scalex() are serialized.

I guess it should explicitly defer to https://drafts.csswg.org/css-transforms/#serialization-of-transform-functions (and other places?) but that is also very vague.

[annevk]

I think WebKit's preference would be to lowercase the function names just as we do with identifiers, but there are some tests currently that test otherwise.

[cdoublev]

Perhaps serialization of case-insensitive identifier-like values in lowercase could be included in the general serialization principles (step 2), which are not yet included in CSSOM (#5642).

Function names are defined as case-insensitive. However, dashed function (mixin) names were defined as case-sensitive <dashed-ident> before (fe94b66). So I am not sure that all function names should serialize in lowercase.

The inconsistency between scaleX() and other CSS functions like linear-gradient(), ie. between camel and kebab case, is unfortunate. 😕