Flex / Actionscript-为什么\'XML.ignoreWhitespace = false\'不起作用？

<?xml version=\"1.0\" encoding=\"utf-8\"?>
<s:Application 
    xmlns:fx=\"http://ns.adobe.com/mxml/2009\" 
    xmlns:s=\"library://ns.adobe.com/flex/spark\" 
    xmlns:mx=\"library://ns.adobe.com/flex/mx\" 
    minWidth=\"955\" minHeight=\"600\"
    creationComplete=\"application1_creationCompleteHandler(event)\"
    >
    <fx:Declarations>
        <!-- Place non-visual elements (e.g., services, value objects) here -->
    </fx:Declarations>

    <fx:Script>
        <![CDATA[
            import mx.events.FlexEvent;
            import mx.controls.Alert;

            XML.ignoreWhitespace = false;

            protected function application1_creationCompleteHandler(event:FlexEvent):void {
                var xmlString:String =
                    \"<sentence><word1>hello</word1><word2> world!</word2></sentence>\";
                trace(xmlString);

                XML.ignoreWhitespace = false;

                var xml:XML = 
                    new XML(xmlString);
                trace(xml.toXMLString());
                Alert.show(xml.toXMLString());
            }

        ]]>
    </fx:Script>
</s:Application>