code: private void updateObjectFields(BioPAXElement update,
  	                                BioPAXElement existing, Model target)
  	{
  		Set<PropertyEditor> editors =
  				map.getEditorsOf(update);
  		for (PropertyEditor editor : editors)
  		{
  			updateObjectFieldsForEditor(editor, update, existing, target);
  		}
  
  //		if (!update.getUri().equals(existing.getUri()))
  //		{
  //TODO addNew a unification xref
  //			if(existing instanceof XReferrable)
  //			{
  //				((XReferrable) existing).addXref(fa);
  //			}
  //		}
  	}
docs: Updates each value of <em>existing</em> element, using the value(s) of <em>update</em>.
  
  @param update   BioPAX element of which values are used for update
  @param existing BioPAX element to be updated
  @param target