VMS Help EXCHANGE, /NETWORK, Qualifiers, /FDL  *Conan The Librarian (sorry for the slow response - running on an old VAX)

       /FDL=fdl-filespec

    Specifies that the output file characteristics are described
    in the File Definition Language (FDL) file. Use this qualifier
    when you require special output file characteristics. For
    more information about FDL files, refer to the OpenVMS Record
    Management Utilities Reference Manual.

    Use of the /FDL qualifier implies that the transfer mode is
    block by block; however, the transfer mode you specify with the
    /TRANSFER_MODE qualifier prevails.