base interface for all event listeners interfaces.
Description
This interface is the callback interface used by the drop target object to
provide notification of Drag and Drop operations that involve the subject
drop target.
Methods of this interface may be implemented to provide "drag under"
visual feedback to the user throughout the Drag and Drop operation.
The drag operation has terminated with a drop on this drop target.
NOTE: This method should not be oneway. The implentation
has to wait until the method XDropTargetDropContext::dropComplete
is called before releasing the data for the drop operation. This
should occur before returning from drop in a normal flow of operation.
Also, the implementor of XDropTargetListener should not assume
the DropTargetDropEvent to be meaningful after returning
from the XDropTargetListener::drop() method.