The DIFFERENCES/CLASS command compares the contents of two
    classes. If CMS finds differences, it creates a file named
    first-class-name.DIF in your current default directory (unless
    /OUTPUT is in effect.) If the contents of the classes are the
    same, it issues a message to that effect and does not create a
    differences file.

    Note: Both classes must reside in the same library of the search
    list or an error will occur.

    A difference is defined as one of the following:

    o  A particular generation of an element is a member of one
       class but no generation of the element is a member of the
       other class.

    o  One particular generation of an element is a member of one
       class and a different generation of the same element is a
       member of the other class.

    Only the generations that differ are displayed in the differences
    file (unless you specify /FULL).

    A heading at the beginning of the differences file includes the
    name of the user that issued the command, the date and time the
    command was issued, and the class names of the two classes being
    compared.