(this codebase is based on: https://github.com/brianmaher84/PlantUML_Notepad-_UDL)
This project contains a User Definied Language (UDL) for Notepad++ to support PlantUML language syntax. It is not a perfect solution as UDL does not support regexes so some PlantUML constructs could not be matched.
https://npp-user-manual.org/docs/user-defined-language-system/#import-a-udl