js获取xml节点的问题..这是怎么回事？

XML code:

<?xml version="1.0" encoding="utf-8" ?>
<imgchange>
<img1>
<imgpath>csdn</imgpath>
<path>sdfsdf</path>
<title>33cxvxcv3</title>
</img1>

<img1>
<imgpath>444</imgpath>
<path>555</path>
<title>666</title>
</img1>

<img1>
<imgpath>444</imgpath>
<path>213</path>
<title>443</title>
</img1>

<img1>
<imgpath>sdf</imgpath>
<path>cxv</path>
<title>sadsd</title>
</img1>
</imgchange>



JScript code:

<script type="text/javascript">
var url="img.xml";
var xmlDoc;
var xmlNodes;
function xmlDom(){
xmlDoc = new ActiveXObject('Microsoft.XMLDOM');
xmlDoc.async = false;
xmlDoc.load(url);
xmlNodes=xmlDoc.getElementsByTagName("img1");
alert(xmlNodes[0].childNodes[0].nodeValue);
}
</script>


我这js获取节点nodeValue本来应该弹出csdn这个值.但是现在为null, 但是我把nodeValue改成nodeName可以弹出imgpath这是为什么？？ 奇怪了
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