system.mfile returns paths to .m files installed with packages.
system.mfile(..., package = "base")system.file.system.mfile is a shortcut for:
system.file('m-files', ..., package = package)
As such it returns empty strings if the requested file does not exist.
If no arguments besides package are passed, it returns the full
path to the package's sub-directory m-files/ -- if it exists.