The DELETE GENERATION command removes information about one or
    more generations of an element. Once a generation is deleted, it
    cannot be restored to its former place in the element in the CMS
    library. You can, however, archive the contents of the generation
    using the /ARCHIVE qualifier and later restore the contents of the
    generation.

    If the generation or range of generations to be deleted has a
    direct descendant generation (that is, a descendant generation on
    the same line of descent), then the changes associated with those
    generations are combined, and then those changes are combined
    with the changes in the descendant generation. If there is
    no descendant generation, that is, the generation or range of
    generations to be deleted is at the end of the line of descent,
    then the changes associated with those generations are discarded.

    You can specify a single generation with the /GENERATION
    qualifier. /GENERATION=1+ is the default. You can also specify
    a range of generations with either the /AFTER or /FROM qualifier
    to delimit the beginning of a range, and either the /BEFORE or /TO
    qualifier to delimit the end of a range. These sets of qualifiers
    can be paired to specify ranges with inclusive or exclusive
    endpoints (see the restriction section).

    If you delete the latest generation on the main line of descent of
    an element that has the reference copy attribute, CMS deletes the
    generation's reference copy and creates a new reference copy that
    corresponds to the generation that is now the latest generation on
    the main line of descent.