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

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

    A zero, if the input condition value did not match any condition
    value in the list, or i-1,  for a match between the first argument
    and the ith argument.