IGBT_EXCLUSIVE_NONE</DT><DD>
This list is also exclusive--at most one option may be selected at a time--but the user can also deselect an item, leaving no items selected. GenItemGroups show a &quot;none-selected&quot; state with GIGS_NONE in their GIGI_<CODE>
selection</CODE>
 instance fields.</DD>
<DT>
GIGBT_EXTENDED_SELECTION</DT><DD>
This list is normally exclusive, unless the user &quot;extends&quot; the selection. The user can extend the selection either by dragging the mouse through another selection 