<?xml version="1.0" encoding="utf-8"?>
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml" >

<mx:Script>
<![CDATA[
     
    import mx.controls.Button;

    private function addStuff(): void
    { 
        var newButton:Button = new Button();
        newButton.label = "new button";
        tw.addChild(newButton);
    }  
    
]]>
</mx:Script>

<mx:Style>
   TitleWindow {
        border-skin: Embed("hearts_skin.png",
           scaleGridLeft="44", 
           scaleGridRight="360", 
           scaleGridTop="54", 
           scaleGridBottom="219");

        paddingTop: 55;
        paddingLeft: 45;
        paddingRight: 45;
        paddingBottom: 40;
}

</mx:Style>
    
<mx:TitleWindow id="tw" title="Happy Valentine's Day" showCloseButton="true" width="400">
    <mx:TextInput id="ta" />
    <mx:Button label="submit" />
</mx:TitleWindow>

<mx:Button label="add child to TitleWindow" click="addStuff()" />
</mx:Application>