MSG-TV-EXPANDING This event is fired after a tree-view item is going to be expanded or collapsed as a consequence of the user's double-clicking a tree-view item with children. EVENT-DATA-1 contains the symbolic values TVFLAG-EXPAND or TVFLAG-COLLAPSE depending on the action performed. EVENT-DATA-2 contains the ID of the parent item. Items can be expanded or collapsed by clicking the [-], [+] or [*] keys, too. Setting EVENT-ACTION to EVENT-ACTION-FAIL prevents the item from being expanded or collapsed.
