The menunem(), itemnum() and subnum() macros let an application break a
menu number down into its component parts--the specific menu number, the
item number and the sub-item number.  (See the section on "menu numbers"
earlier in this chapter for details.)  Intuition also supplies macros that
allow an application to construct a menu number given its components:

SHIFTMENU(n)
    Create a properly masked and shifted specific menu number.

SHIFTITEM(n)
    Create a properly masked and shifted item number.

SHIFTSUB(n)
    Create a properly masked and shifted sub-item number.

FULLMENUNUM( menu, item, sub )
    Create a complete composite menu number from its components.