code: protected final void fireVetoableChange(String propertyName, 
                      Object oldValue, Object newValue)
                      throws PropertyVetoException {
          vcs.fireVetoableChange(propertyName, oldValue, newValue);
      }
docs: Report a vetoable property update to any registered listeners.  If
  anyone vetos the change, then fire a new event reverting everyone to
  the old value and then rethrow the PropertyVetoException.
  <p>
  No event is fired if old and new are equal and non-null.
  
  @param propertyName  The programmatic name of the property
  that is about to change..
  @param oldValue  The old value of the property.
  @param newValue  The new value of the property.
  @exception PropertyVetoException if the recipient wishes the property
  change to be rolled back.