1.2.48 $MACRO : Allow use of macros.

In the {$MACRO ON} state, the compiler allows the use of C-style (although not as elaborate) macros. Macros provide a means for simple text substitution. This directive is equivalent to the command line option -Sm. By default, macros are not allowed.

More information on using macros can be found in section 2.2, page 283.