Q: In looking through supplied macros I came across the command: &M_ACT X.XXX NULL. What does this do?
REV 7.00

A: This specifies that the menus for which "XXXXX" will be valid are those in which "NULL" is a valid command. In addition, MOSES has no valid commands when "reading a model", and all macros are valid during this phase. Now, since "NULL" is never a valid command, the above says that "XXXXX" is valid only when reading a model.