哪位高手帮忙看一下这段Flex代码错在哪里

<?xml version="1.0" encoding="utf-8"?>
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml" layout="absolute" fontSize="12">
<mx:Script>
<![CDATA[
public var selectedNode:XML;
//当点选了tree组件中的不同节点时
public function treeChanged(event:Event):void{
//event.target代表tree组件,而tree组件的selectedItem代表了当前选中节点的XML数据
selectedNode=Tree(event.target).selectedItem as XML;
//输出选中节点的label属性值
res_txt.text=""+selectedNode.@label

}
]]>
</mx:Script>
<mx:XMLList id="files">
<folder label="C:">
<folder label="My Document">
<folder label="Adobe"/>
</folder>
<folder label="Windows">
<folder label="soft"/>
<folder label="workSpaces"/>
</folder>
<folder label="Drivers"/>
<folder label="linux driver"/>
</folder>
</mx:XMLList>
        //提示我这行有错
<mx:Tree id="myTree" width="119" height="265" labelField="@label" showRoot="true" dataDescript