As I said in PR12, the API docs is missing, and it turns out it should be in a doc comment to this function (see `@builtin` above). I'll write that.

I have also put together https://en.opensuse.org/openSUSE:YaST:_UI,_User_Interface_Library linked from https://en.opensuse.org/openSUSE:YaST_development#Components so that we better communicate what docs we have and where to change it.