VMS Help DTM, FILTER, Command Qualifiers, /USER_FILTER  *Conan The Librarian (sorry for the slow response - running on an old VAX)

   /USER_FILTER=filename
   /USER_FILTER=(filename[,...])
   /NOUSER_FILTER (D)

   The specified files are executed by DEC Text Processing Utility
   (DECTPU). If more than one file is specified they are executed in
   the order given. The user filters are applied before any
   built-in filters that are also specified on the command line.

   User filter files can be located either in OpenVMS directories or in
   Compaq Code Management System (CMS) libraries. Files may be
   specified using logical names including logical names that specify
   search lists. Wildcards cannot be used. For files in CMS libraries,
   the most recent generation on the main line of descent is used.

   Before the first file is executed the file to be filtered is read
   into the DECTPU buffer "filter_buffer". Next, the file specified by
   the logical name DTM$UFDEFINES is executed. The system logical name
   DTM$UFDEFINES references the file SYS$LIBRARY:DTM$UFDEFINES.TPU,
   which contains definitions of a global replace procedure and
   patterns which can be used in building filters. This logical can be
   redefined to point to a custom file.

   Any errors in accessing the user filter files or in executing the
   DECTPU commands will be reported. However, they will not cause the
   FILTER command to fail, and any remaining user and built-in filters
   will be applied.

   After all the user filters have been applied, the file being
   filtered will be written out. If any built-in filters are also
   specified, they are applied to the newly created file, resulting in
   a second new version.