title: How do I limit tree nodes from being dragged from their current node in flex 3?
body: <p>So I have a flex tree component with a xmllistcollection as it's data provider. I would like to be able to rearrange the leaves and branches in the tree by drag and drop. I want to limit the drop area to the current level of the item being dragged. Like 
        <pre>
        branch
         branch 0
           leaf 1
           leaf 2
         branch x
           leaf a
           leaf b
         </pre>
  So, branch x can't be moved under branch 0 and leaf a could not be moved under branch 0.</p>