Reported when the tree has at least one group in its ‘DropAccept’ list and an item from an accepted source is being dragged over it. The message reports (item-index in your ŒIO)(token from drag source)(mode)(menu)(group1 of source)(group2 ...) as an n-element vector. In the message, mode is 0 for move, 1 for copy; menu is 0 for a normal drop, 1 for a menu request (right-button drag). You may reject the event – otherwise the item will be highlighted.