<?xml version="1.0"?>
  <mx:Object xmlns:mx="http://www.adobe.com/2006/mxml" implements="mx.core.IMXMLObject">
    <mx:Script>
      <![CDATA[
        private var total:Number;
        public var a:Number;
        public var b:Number;
        // You must define the initialized() method when implementing IMXMLObject.
        public function initialized(document:Object, id:String):void{
          total=a+b;
        } 
        public function getTotal():Number{
          return total;
        }
      ]]>
    </mx:Script>
  </mx:Object>