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

       /CONCURRENT
       /NOCONCURRENT

    Controls whether an element reserved by you can be reserved by
    another user while you have it reserved. The initial setting is
    /CONCURRENT.