VMS Help MACRO, VAX MACRO Assembler, Directives, .MACRO  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    Begins the definition of a macro.

      .MACRO macro-name  [formal-argument-list]
            ...
           range
            ...
      .ENDM [macro name]

    macro-name

    The name of the macro to be defined;  this  name  can  be  any
    legal symbol up to 31 characters long.

    formal-argument-list

    The symbols, separated by  commas,  to  be  replaced  by  the
    actual arguments in the macro call.

    range

    The source text to be included in the macro expansion.

    If the name specified is the same as the name of a previously
    defined macro,  the  previous definition is deleted and replaced
    with the new one.  The .MACRO directive is followed  by  the
    source  text  to  be included  in  the macro expansion.  The .ENDM
    directive specifies the end of the range.

    If a macro has the same name as a  VAX  opcode,  the  macro  is
    used instead  of  the instruction.  This feature allows you to
    temporarily redefine an opcode.

    If a macro has the same name as a  VAX  opcode  and  is  in  a
    macro library,  you  must  use  the  .MCALL  directive to define
    the macro. Otherwise, because the symbol is already defined (as the
    opcode), the assembler will not search the macro libraries.