Overriding event listeners

programming flash
1

I am working on a Flash demo (all AS3) that requires a scrollbar. I wanted to create my own so on searching I found this Kirupa tutorial. I learned it an incorporated everything (also went well beyond) and the end product works nicely.

There is one aspect of the code provided in this tutorial that has me very confused and, although my code includes it and everything works, it bugs me to not understand it. It’s this part of the Scrollbar class:

    /**
    * Override the add and remove event listeners, so that SliderEvent.CHANGE events will be 
    * subscribed to the Slider directly.
    * 
    * There is issues with this however, Event.CHANGE events will get subscribed directly too Slider as well.
    */
    public override function addEventListener( type:String, listener:Function, useCapture:Boolean=false, priority:int=0, useWeakReference:Boolean=false ):void
    {
        if ( type === SliderEvent.CHANGE )
        {
        slider.addEventListener( SliderEvent.CHANGE, listener, useCapture, priority, useWeakReference );
        return;
        }
        super.addEventListener( type, listener, useCapture, priority, useWeakReference );
    }
    public override function removeEventListener( type:String, listener:Function, useCapture:Boolean=false ):void
    {
        if ( type === SliderEvent.CHANGE )
        {
        slider.removeEventListener( SliderEvent.CHANGE, listener, useCapture );
        return;
        }
        super.removeEventListener( type, listener, useCapture );
    }

Obviously since I don’t understand it the explanation in the commented header doesn’t work for me. Can anyone explain what such an override accomplishes in more simple terms?

Thanks!