The Modify Library... menu item is used to modify the
  attributes of one or more libraries:

  o  It establishes or removes the connection between
     the current CMS library and its reference copy
     directory.

  o  It establishes the file revision time, concurrent
     and keep attributes.

  Modify Library does not add files to or delete files
  from a reference copy directory.  Once you establish a
  reference copy directory for a library, subsequent
  transactions that create new element generations on the
  main line of descent also update the reference copy
  directory (provided the element also has the reference
  copy attribute).

  Use the following steps to display a library's
  attributes:

  1. Click on the library name.
  2. Pull down the View menu.
  3. Choose the Expand submenu.
  4. Choose the Attributes menu item.