Formally supporting undocumented namespaces

[scottbedard]

My team and I are working to modernize a very large codebase, and would like the guard rails for our design system to be as strict as possible.

There are undocumented namespaces we would like to use, but feel uncomfortable relying on behavior that is outside the official API. See original conversation here →

The specific namespaces that would be useful to us are --background-color, --border-color, and --text-color.

What would be involved in making these APIs officially supported? I'd be happy to add any tests and documentation necessary to cover these features.