OpenVMS usage:longword_signed
    type:         longword (signed)
    access:       write only
    mechanism:    by value

    Position in source-string where a nonmatch was found.

    On Alpha 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.

    Returned
    Value         Condition

    0             Either all characters in source-string match some
                  characters in set-of-characters, or there were no
                  characters in set-of-characters.
    1             Either the first nonmatching character in source-
                  string was found in position 1, or there were no
                  characters in source-string.
    N             The first nonmatching character was found in
                  position N within source-string.