ActionScript 3.0 :: How Does Event.ADDED_TO_STAGE Work

I'm attempting to initiate a set of variables within a movie clip myElement as soon as it's dynamically loaded onto the stage:

frame1 within myElement:

PHP Code:

this.addEventListener(Event.ADDED_TO_STAGE,  initiateVars); function initiateVars(ev:Event):void{         var currentY:int = this.y;     var currentX:int = this.x; } 

I'm trying to make this happen only once, and only when myElement is first placed on stage, but the code above doesn't work. Am I misusing the ADDED_TO_STAGE event?