How can he update a non-existent string?

Question

I suppose 40 years of imperative programming has rendered me unable to comprehend this new-fangled style of Declarative programming! :-(
Here's a short program from a Flex book which I can't understand.
At Initialization of the mx:Panel, which is supposed to be triggered BEFORE the panel is created, he writes into a text string, "event_txt.text", which is defined WITHIN mx:Panel, ie: AFTER the panel has been created.
And it Works! ??
How can event_txt be updated before it has been created?
OK, I must be confused about when 'initialize' is triggered.
Can anyone straighten me out?
Is there a preliminary compiler scan BEFORE 'initialization" to pick up all the variable names?
If so, what else happens before "initialization"?
Thanks!
<?xml version="1.0" encoding="utf-8"?>
<!--
// Flex Solutions: Essential Techniques for Flex 2 and Flex 3 Developers
// Author: Marco Casario // All Rights Reserved.
// Solution 1-5: Understanding the Flex event model
// @author Marco Casario// @date 26 November 2007// @version 1.0// @site flexsolutions.comtaste.com
-->
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml"
    initialize="event_txt.text += '\n Application initialize fired'"
    creationComplete="event_txt.text += '\n Application creationComplete fired'" >
    <mx:Panel title="Handling System Events"
           initialize="event_txt.text += ('\n Panel initialize fired')" width="372" height="234"  <!-- here's the Initialize statement -->
        creationComplete="event_txt.text += ('\n Panel creationComplete fired')" >
        <mx:TextArea editable="false" height="100%" width="100%" 
            id="event_txt" />                                                                 <!-- this string isn't defined till AFTER initialization, right? -->
    </mx:Panel>
</mx:Application>
<!--
///////////// OUTPUT  ///////////////////
//Panel initialize fired
// Application initialize fired
// Panel creationComplete fired
// Application creationComplete fired
-->

Answer 1

Read that link Michael provided, but in short, step 9 says the following, which indicates that when the initialize event is fired, the components inside the Panel have been initialized, but they have not been sized or laid out.
9) Dispatches the initialize event on the component. At this time, all of the component's children are initialized, but the component has not been sized or processed for layout. You can use this event to perform additional processing of the component before it is laid out.