title: Extjs 4 Explain drag and drop how to implement across two grids or treepanels
body: <p>Using Extjs 4.07</p>
  
  <p>Assume I have two treePanels or, more likely, two grids. I want to be able to drag items back and forth between the two. What are the basic mechanisms required to do this? I'd liek to see some sample code demonstrating how it is done. I've not been able  to find good documentation on how to do this that is applicable to v4 and not v3. I know there is an easy way and I've found many documents explaining bloated ways of doing this. I don't understand how dd is implemented in general. So, a high level overview would be useful as well.</p>