VMS Help CMS, INSERT, GENERATION, Restrictions  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    o  You cannot insert an element generation into a class that has
       read-only access.
    o  A class can contain only one generation of any particular
       element.
    o  You cannot insert a generation into a class in another library
       (the generation and class must be in the same library).