A VetoableChange event gets fired whenever a bean changes a "constrained"
property. You can register a VetoableChangeListener with a source bean
so as to be notified of any constrained property updates.
This method gets called when a constrained property is changed.
Parameters: evt - a PropertyChangeEvent object describing theevent source and the property that has changed. exception: PropertyVetoException - if the recipient wishes the propertychange to be rolled back.