VMS Help CMS, CREATE, LIBRARY, Qualifiers, /BEFORE[=directory-specification]  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    Instructs CMS to insert new libraries into the existing library
    search list immediately in front of the existing specified
    directory. The specified directory must be in the existing
    library search list. If you omit the directory specification, CMS
    automatically adds the libraries (in the order you specify) to the
    front of the list. You cannot specify both /AFTER and /BEFORE on
    the same command line. If neither /AFTER nor /BEFORE is specified,
    the CREATE LIBRARY command's library list supersedes any existing
    search list.