/sys$common/syshlp/helplib.hlb SCA, SCA Topics, Glossary, hidden_modules  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    A module in one of the libraries in the current library list which
    is also present in a library which is earlier in the library list.
    The module in the earlier library is visible. The same module in
    any later library is a hidden module, hidden by the first module.