Variables with names beginning with the string "DTM$UF_
  " are used to control user filters. These variables
  must be logical variables but can be global or local.

  When tests are run that have associated variables whose
  names begin with the string "DTM$UF_", DTM will apply
  the user filters contained in the files referenced by
  the value of those variables. Only a single file may be
  referenced by each variable.

  The specified files are executed by DEC Text Processing
  Utility (DECTPU). If more than one user filter variable
  is associated with a test, the files are executed in
  the lexicographic order of the variable names. The user
  filters are applied before any built-in filters that
  are also specified for the test.

  User filter files can be located either in OpenVMS
  directories or in 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 operation 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.

  In order to disable a user filter that is defined
  with a global variable for a particular test, define
  the value of the variable for the test as a string
  containing only spaces.