I have looked into your example file and the wordfile and made some changes without really knowing how the code in the example file should be highlighted.
I have changed the function strings.
The 3 pairs of marker characters have been replaced by a substring definition.
The list of delimiters is just resorted (not really necessary, but I like sorted delimiters).$J
was duplicate in /C2 and /C3. I have deleted it from /C3. This duplicate keyword was detected by my ultimate test for duplicate words macro
The keywords have been resorted with my ultimate word definitions sorting macro
I have edited your post and replaced your MUMPS language definition with my version because your wordfile is already in the ZIP archive and I want to avoid loads and scrolls more than necessary in this topic for all users.
Test my modifications and tell me if they are helpful or making it worser.