So in this MUMPS command, are we jumping to label meth in a file named by a variable called blurfl? If we're not, I don't know what the percent sign is doing. There is no file called %blurfl.m in my application.
GOTO meth^%blurfl
You can't have filenames that begin with % in Unix/Linux, so the file is actually named _blurfl. When the mumps system sees %blurfl, it does the translation and loads the correct file.
In this case the command is issuing a goto to the meth label in the %blurfl routine, which is actually named _blurfl.m