/sys$common/syshlp/helplib.hlb CMS, DIFFERENCES, file, Qualifiers, /OUTPUT[=file-specification]  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    Directs CMS to write output to the specified file. CMS creates a
    new file if you do not specify /APPEND. If you omit the /OUTPUT
    qualifier (or if you specify /OUTPUT but do not provide a file
    specification), CMS creates a file with the file name specified in
    the file1 parameter and the file type .DIF. If you specify a file
    name but omit the file type component, CMS writes the output to a
    file with the specified file name and a file type of .DIF.