context

    OpenVMS usage:context
    type:         longword (unsigned)
    access:       write only
    mechanism:    by reference
    Value identifying the data stream that DCX$COMPRESS_DONE deletes.
    The context argument is the address of a longword containing
    this value. DCX$COMPRESS_INIT writes the value into the context
    argument; you should not modify its value. You can define
    multiple context arguments to identify multiple data streams
    that are processed simultaneously.