How to move items between lists in jQuery but limiting the levels of nesting?
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I have a nested list that uses jQuery's sortable functionality to reorder them.
The list has a maximum of 3 levels: grandparents, parents and children. I have set up an example on [jsfiddle][1]

I need to be able to drag all items to reorder, and move items between lists however, it can't have any more than 3 levels, so a Grandparent of Parents and Children must be prevent from being moved into another list entirely, whilst a Parent with Children can only be moved to to another Grandparent, not inside a Parent or Child, etc.

Is this possible? If needs be, the markup can be changed.

  [1]: http://jsfiddle.net/abunchofletters/yXdxx/