OpenVMS usage:longword_unsigned
    type:         longword (unsigned)
    access:       write only
    mechanism:    by value

    The relative position of the first character of the substring if
    found, or zero if not found.

    On Alpha and I64 systems, if the relative position of the
    substring can exceed 2**32-1, assign the return value to a
    quadword to ensure that you retrieve the correct relative
    position.