This property sets and gets the drop flag. When we drag item A over item B, a
DragEvent (with type dragOver) is fired on item B. If the canDrop property of this
event is true, we will be able to drop item A on item B. Otherwise, we will see a
forbidden cursor which indicates that we can not drop item A on item B.
<box on:dragOver="onDragOver();"/>
function onDragOver()
{
var eventObj = shell.currentEvent;
if (eventObj)
{
// prevent this box from being a drop target.
eventObj.canDrop = false;
}
}