/LABELS=LOWER generates object modules with case sensitive labels.

/LABELS=UPPER generates object modules with labels in upper-case, that is, not case sensitive.

By default, the compiler operates with /LABELS=LOWER and produces object modules that respect the case of M labels.

Because GT.M stores routines in RMS files and RMS does not support lower-case file names, GT.M always treats routine names as upper-case.