drag'n'drop between multiple trees, droppables option

solved.

one can achieve the thing I wanted solely by implementing Mif.Tree.Drag callbacks passed via it's constructor:

for left tree:
     onDrag: function() { this.where='notAllowed';  }

    this forbids to drop anything in the left tree.

for right tree:
  beforeDrop:function(current, target, where) {
    this.action = (current.tree === tree) ? 'copy' : 'move'; // assuming tree is the global variable for left tree
    this.drop();
  }

  this is necessary so that, if node is dragged from left tree to right tree it must be COPIED
  however if a node is dragged from and dropped to the right tree - it must be MOVED

Several assumptions:
The library is great, though IMHO naming is in some cases not perfect, and naming DOES MATTER especially when the thing grows.

1) Why is this callback for left tree I had to use is called onDrag? It's about dropping. That's very confusing.
    Maybe I'm using the wrong callback for the thing (I've copied this from some other forum post)
    If so - what would be the right one?
2) If something is called "beforeDrop", one expects that drop would occure anyway after this callback,
    however, it does not and one must explicitely call this.drop().
    This callback should have rather been called onDrop, or something, but "before" does not really fit here.

In any case - MANY thanks for your work and this great library!