VMS Help CMS, DIFFERENCES, file, Qualifiers, /GENERATION[=generation-expression]  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    Directs CMS to search for an element generation in the current
    CMS library. The /GENERATION qualifier must immediately follow
    the element name to which it applies. If you specify /GENERATION
    but do not provide a generation expression, CMS uses the latest
    generation on the main line of descent.