The lexers are part of the separate [Scintilla project](https://www.scintilla.org/index.html) which has all the docs on how to write them. Note that Geany uses Scintilla 3 not Scintilla 4 so you can't rely on anything thats not backported.
You should get your lexer accepted there first. -- You are receiving this because you are subscribed to this thread. Reply to this email directly or view it on GitHub: https://github.com/geany/geany/issues/2350#issuecomment-540903149
