code: public void addPropertyChangeListener(PropertyChangeListener listener) {
  		if (listener instanceof PropertyChangeListenerProxy) {
  			PropertyChangeListenerProxy proxy = (PropertyChangeListenerProxy) listener;
  			addPropertyChangeListener(proxy.getPropertyName(), (PropertyChangeListener) proxy.getListener());
  		}
  		else {
  			if (listeners == null) {
  				listeners = new EventListenerList();
  			}
  			listeners.add(PropertyChangeListener.class, listener);
  		}
  	}
docs: Add a PropertyChangeListener to the listener list. The listener is
  registered for all properties.
  
  @param listener The PropertyChangeListener to be added