VMS Help CMS, CREATE, LIBRARY, Qualifiers, /EXTENDED_FILENAMES  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    Used to create a CMS library that allows the use of extended file
    names. This qualifier is only available on OpenVMS V7.2 and later.
    Use /NOEXTENDED_FILENAMES to create a CMS library that does not allow
    the use of extended file names. /NOEXTENDED_FILENAMES is the default.
    Use MODIFY LIBRARY to change this attribute on an existing library.