ockquote>
 The class defined callback methods should be used when the callback method requires
 access to non-public methods and/or fields of the class. 
 <p>
 The external listener callback mechanism enables the registration of a <a href="Unmarshaller.Listener.html" title="class in jakarta.xml.bind"><code>Unmarshaller.Listener</code></a> 
 instance with an <a href="#setListener(jakarta.xml.bind.Unmarshaller.Listener)"><code>setListener(Listener)</code></a>. The external listener receives all callback event