e three functions and two events you need to use to control a drag-drop operation.
The first thing to understand is that during a drag-drop operation the control places
two things into the OLE <span class="code">Data</span> object associated with the drag-drop:
</p><ol><li>The Text of the node being dragged.</li><li>A private data format containing information allowing any TreeView control to 
determine which node is being dragged, and which control it was sourced from.</li></ol><p>
Whenever a node is being