UndoOperation  - AS3

package flashx.textLayout.operations.examples
{
    import flashx.textLayout.elements.TextFlow;
    import flashx.textLayout.events.FlowOperationEvent;
    import flashx.textLayout.operations.FlowOperation;
    import flashx.textLayout.operations.UndoOperation;
    
    public class UndoOperation_example
    {
        public function attach(textFlow:TextFlow):void
        {
            textFlow.addEventListener(FlowOperationEvent.FLOW_OPERATION_BEGIN, opBeginHandler);
        }
        
        public function opBeginHandler(evt:FlowOperationEvent):void { 
            var flowOp:FlowOperation = evt.operation; 
            if(flowOp is UndoOperation) {
                //user has the option to cancel undo operation
                if(!verifyUndo(flowOp.textFlow) && evt.cancelable) {
                    evt.preventDefault();
                }
            }
        }
        private function verifyUndo(tf:TextFlow):Boolean {
            //verify whether user wants to undo this operation
            return false;
        }
    }
}