Library /sys$common/syshlp/lse$clihelp.hlb SET, SOURCE_DIRECTORY, Qualifiers, /BEFORE  *Conan The Librarian (sorry for the slow response - running on an old VAX)

       /BEFORE
       /BEFORE[=directory-spec]

    Specifies that LSE should insert the directory or directories
    indicated into the list of source directories in front of the
    directory you specify as the value on the qualifier. If you do not
    specify a directory-spec value, the directory or directories are
    added at the front of the list.

    If you do not specify either the /BEFORE qualifier or the /AFTER
    qualifier, LSE replaces the entire directory list.