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

    Replaces a formal argument with successive actual arguments
    specified in an argument list.

       .IRP symbol,<argument list>
             ...
            range
             ...
       .ENDR

    symbol

    A formal argument that is successively replaced  with  the
    specified actual  arguments  enclosed in angle brackets.  If no
    formal argument is specified, the assembler displays an error
    message.

    <argument list>

    A list of actual arguments enclosed in angle  brackets  and  used
    in expanding  the  indefinite  repeat  range.   An  actual
    argument can consist of one  or  more  characters.   Multiple
    arguments  must  be separated  by a legal separator (comma, space,
    or tab).  If no actual arguments are specified, no action is taken.

    range

    The block of source text to be repeated once for each  occurrence
    of an  actual  argument  in  the  list.   The  range  can  contain
    macro definitions and repeat ranges.  .MEXIT is legal within the
    range.

    This  replacement  process  occurs  during  the  expansion   of
    the indefinite repeat block range.