http://topic.csdn.net/u/20080112/14/cffa064a-4740-4e8c-a7d6-2797a563ffd4.html
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title>Untitled Page</title>
</head>
<body>
<script type="text/javascript">
alert(document.firstChild.nodeValue);
alert(document.childNodes[0].nodeValue);
</script>
</body>
</html>
<head>
<title>Untitled Page</title>
</head>
<body>
<script type="text/javascript">
alert(document.firstChild.nodeValue);
alert(document.childNodes[0].nodeValue);
</script>
</body>
</html>
愚公注：
上述方法仅适用于IE，且有个BUG：IE将DOCTYPE元素当做是注释，nodeValue时会去掉前4个字符和后3个字符。