Library /sys$common/syshlp/cms$dw_help.hlb OCC, Occ etb  *Conan The Librarian (sorry for the slow response - running on an old VAX)

  The Elements button controls occlusion of elements. When
  this button is activated, CMS searches for and acts upon
  the first occurrence of an element found in a library
  (the first library that contains the element) in the
  library search list.

  If this button is off, CMS acts upon each occurrence of
  the element or elements found in the library search list.