Disable dropping on elements

[themikegreider]

Hello - I have a tree view with folders and documents nested. I would like to be able to disable the dropping event on other documents, but continue to allow inside of folders. I see the option to prevent dragging, but I don't see a way to specify targets (which would be the other documents) that can't be dropped on. The end result is that documents can only be dragged / dropped into other folders. Can someone point me in the right direction?