The droppableOver event is fired when a valid draggable target is placed over a TreeView node that can accept a drag (e.g. a non disabled one).
This event can be cancelled - in this case there will be no droppable hover state change for the node.

The following additional properties are set to the event object:
- element - the node being dragged;
- draggable - the element being dragged;
- droppable - the droppable element over which the draggable one is placed. This will be different from the node;
- valid - whether the drop is allowed. Setting this to false will disable the drop operation and will not add any valid drop indications such as highlighting or different style.

<ul id="treeview">
    <li>My Project
            <li id="someid">js</li>

<script type="text/javascript">
    jQuery(function ($) {
            events: {
                droppableOver: function(e) {
                    // disable the drop
                    e.valid = false;