l root element to Jakarta XML Binding mapped <code>declaredType</code>
 and return the resulting content tree.
 
 <p>
 This method implements <a href="#unmarshalByDeclaredType">unmarshal by declaredType</a>.
 <p>
 This method assumes that the parser is on a START_DOCUMENT or
 START_ELEMENT event. Unmarshalling will be done from this 
 start event to the corresponding end event.  If this method 
 returns successfully, the <code>reader</code> will be pointing at 
 the token right after the end event.</div>
<d