Accessing application attributes

How can I access apllication attributes? For exemple, I want to do that:

<?xml version="1.0" encoding="utf-8"?>
<mx:Application name="SimpleApplicationExample" xmlns:fx="http://ns.adobe.com/mxml/2009" 
                xmlns:s="library://ns.adobe.com/flex/spark" xmlns:mx="library://ns.adobe.com/flex/mx" width="500">

<mx:Label text="application.width" />


</mx:Application>

evidently, this code will not run; but do you understand what I want?