SUBROUTINE:
SUBROUTINES are extremely similar to PROCEDURES
except that results declared in a SUBROUTINE are not
visible to the main macro, as they are in PROCEDURES.
The main macro results are still visible in the SUBROUTINE.SUBROUTINES and PROCEDURES
share the same namespace (i.e. You can't have both a procedure named
DOSTUFF and a subroutine named DOSTUFF).