SelectionEvent  - AS3

         // Find selected element range
         var range:ElementRange = ev.selectionState ?  
             ElementRange.createElementRange(ev.selectionState.textFlow,
             ev.selectionState.absoluteStart, ev.selectionState.absoluteEnd) : null;

package flashx.textLayout.events.examples {
    import flash.display.Sprite;
    import flashx.textLayout.container.ContainerController;
    import flashx.textLayout.edit.ElementRange;
    import flashx.textLayout.elements.TextFlow;
    import flashx.textLayout.elements.ParagraphElement;
    import flashx.textLayout.elements.SpanElement;
    import flashx.textLayout.edit.SelectionManager;
    import flashx.textLayout.edit.SelectionState;
    import flashx.textLayout.events.SelectionEvent;

    public class SelectionEvent_example extends Sprite
    {
        private var tf:TextFlow;
        private var sm:SelectionManager;
        
        public function SelectionEvent_example()
        {
            //define TextFlow and manager objects
            tf = new TextFlow();
            sm = new SelectionManager();
            tf.interactionManager = sm;
            
            //define elements to contain text
            var p:ParagraphElement = new ParagraphElement();
            var s:SpanElement = new SpanElement();
            s.text ="This is sample text for the SelectionEvent example.";
                  
            //add the elements to the TextFlow
            p.addChild(s);  // add span as child of paragraph
            tf.addChild(p);  // add paragraph to text flow   
                    
            //compose TextFlow to display
            tf.flowComposer.addController(new ContainerController(this,600,400));
            tf.flowComposer.updateAllControllers();
            
            //add event handler to listen for SelectionEvent
            tf.addEventListener(SelectionEvent.SELECTION_CHANGE, selectionHandler);
    
        }
        private function selectionHandler(ev:SelectionEvent):void{
            trace("Selection event detected.");
            
            // Find selected element range
            var range:ElementRange = ev.selectionState ?  
                ElementRange.createElementRange(ev.selectionState.textFlow,
                ev.selectionState.absoluteStart, ev.selectionState.absoluteEnd) : null;

            trace("Starting index of selection range: " + range.absoluteStart);
            trace("Ending index of selection range: " + range.absoluteEnd);
        }
       
    }        
}