VMS Help LBR Routines, LBR$LOOKUP_KEY, Description  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    If LBR$LOOKUP_KEY finds the specified key, it initializes
    internal tables so you can access the associated data.

    This routine returns the RFA (consisting of the virtual block
    number (VBN) and the byte offset) to the 2-longword array
    referenced by txtrfa. Note that the RFA is only 6 bytes long.