@cll142 ,
Please note that UDL is not an infinitely-configurable solution; there are times that your desired styling for a language goes beyond what UDL can offer.
At that point, your choices are to write a full lexer plugin which can be distributed as a DLL or through the Plugins Admin; if that’s beyond your scope, you might get the extra highlighting you want by using the Python Script plugin and the script EnhanceAnyLexer.py that @Ekopalypse shares in his github repo, which allows you to add extra highlighting to a builtin lexer (like the HTML lexer) or to a User Defined Language (UDL) using regexes.
So if you cannot get the UDL “good enough”, do as much as you can, then try Eko’s script. If that still doesn’t cover your needs, writing a lexer plugin is the next option.