code: public void vetoableChange(PropertyChangeEvent evt) throws PropertyVetoException {
          // monitor "beanContext" property
          if ("beanContext".equals(evt.getPropertyName())
                  && contains(evt.getOldValue())) {
              // noop: at this point doesn't veto
          }
      }
docs: This method gets called when a constrained property is changed.
  
  @param evt a <code>PropertyChangeEvent</code> object describing the
  event source and the property that has changed.
  @throws java.beans.PropertyVetoException
  if the recipient wishes the property
  change to be rolled back.