I want to be able to re-order the root nodes of the TreePanel.
However, I do not want one root node to become a child of another root node.
So far I've tried to override TreePanelDropTarget's showFeedback method.
It looks like (1)the target when re-ordering root nodes on the same level and (2) dragging root nodes to become the child of other root nodes are the same.
How can I differentiate between these 2 operations?