VMS Help RTL Routines, OTS$, OTS$SCOPY_R_DX, Returns  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    OpenVMS usage:word_unsigned
    type:         word (unsigned)
    access:       write only
    mechanism:    by value

    Number of bytes not moved to the destination string if the length
    of the source string pointed to by source-string-address is
    greater than the length of destination-string. Otherwise, the
    value is 0 (zero).