.IRP replaces a formal argument with successive actual arguments
    specified in an argument list. This replacement process occurs
    during the expansion of the indefinite repeat block range. The
    .ENDR directive specifies the end of the range.

    .IRP is similar to a macro definition with only one formal
    argument. At each successive expansion of the repeat block, this
    formal argument is replaced with successive elements from the
    argument list. The directive and its range are coded in line
    within the source program. This type of macro definition and
    its range do not require calling the macro by name, as do other
    macros described in this section.

    .IRP can appear either inside or outside another macro
    definition, indefinite repeat block, or repeat block (see the
    description of .REPEAT). The rules for specifying .IRP arguments
    are the same as those for specifying macro arguments.