A synopsis (css microsyntax + default) should be enough to define an extension property

[dwarring]

Which probably involves compiling and EVALing to a Raku token (pre RakuAST at least).

[dwarring]

We now have CSS::Specification::Compiler, which is an unreleased Raku module.

It currently just has a back-office function of regenerating rules for CSS::Module (See make-modules.raku).

The plan is to integrate it into CSS:Properties for dynamic use, but warting for RakuAST to become more official, and the module to stabilize.