VMS Help DECTPU, TPU$EDIT, Description  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    This routine builds a command string and passes it to TPU$TPU. If
    the length of the output descriptor is nonzero, then the /OUTPUT
    qualifier is added to the command string. The /OUTPUT qualifier
    causes a file to be written to the specified file even if no
    modifications are made to the input file. If the QUIT built-
    in procedure is called, it prompts the user as if changes had
    been made to the buffer. This allows applications to check for
    the existence of the output file to see if the editing session
    was terminated, which is consistent with other OpenVMS callable
    editors.

    If your application parses information that is not related to the
    operation of DECTPU, make sure the application obtains and uses
    all non-DECTPU parse information before the application calls
    TPU$EDIT. Your application must do this because TPU$EDIT destroys
    all parse information obtained and stored before TPU$EDIT is
    called.