.IRPC is similar to .IRP except that .IRPC permits single-
    character substitution rather than argument substitution. On each
    iteration of the indefinite repeat range, the formal argument is
    replaced with each successive character in the specified string.
    The .ENDR directive specifies the end of the range.

    .IRPC is similar to a macro definition with only one formal
    argument. At each expansion of the repeat block, this formal
    argument is replaced with successive characters from the actual
    argument string. The directive and its range are coded in line
    within the source program and do not require calling the macro by
    name.

    .IRPC can appear either inside or outside another macro
    definition, indefinite repeat block, or repeat block (see
    description of .REPEAT).