I have this ActionScript code here:

package 
{
    import flash.display.Sprite;

    import flash.display.LineScaleMode;
    import flash.display.CapsStyle;
    import flash.display.JointStyle;

    import flash.display.Shape;
    import flash.events.Event;

    public class Main extends Sprite 
    {

        private var lines:Shape;

        public function Main():void 
        {
            if (stage) init();
            else addEventListener(Event.ADDED_TO_STAGE, init);
        }

        private function init(e:Event = null):void 
        {
            removeEventListener(Event.ADDED_TO_STAGE, init);
            // entry point

            lines = new Shape();
            addChild(lines);

            lines.graphics.clear();
            lines.graphics.lineStyle(10, 0x000000);

            lines.graphics.moveTo(0, 0);

            lines.graphics.lineTo(stage.stageWidth, stage.stageHeight);
        }

    }

}

What I'm expecting this to do is to draw a line from one corner of the screen to the other... but that's not what it does. See here.