VMS Help RTL Routines, LIB$, LIB$VERIFY_VM_ZONE_64, Argument  *Conan The Librarian (sorry for the slow response - running on an old VAX)

 zone-id

    OpenVMS usage:identifier
    type:         quadword (unsigned)
    access:       read only
    mechanism:    by reference

    Zone identifier of the zone to be verified. The zone-id argument
    is the address of an unsigned quadword that contains this zone
    identifier. A value of 0 indicates the 64-bit default zone.