Fill in the Reference Copy field with the name of an
  empty OpenVMS directory to be used for reference copies of
  library elements.

  If the Reference Copy Directory button is activated, CMS
  stores copies of elements belonging to the library in the
  reference copy directory.  You must also specify an OpenVMS
  directory name in the Reference Copy Directory field.

  The directory cannot be a CMS library, nor can it be a
  subdirectory of a CMS library directory.

  Although CMS allows you to assign the same reference copy
  directory to different libraries, it is strongly
  recommended that you assign each CMS library its own
  unique reference copy directory.

  Wildcards are not allowed.