为什么我查找body的父节点会告诉我没有呢？单独查找body也会显示null
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>遍历节点</title>
<script type="text/javascript">
var oHtml=document.documentElement;
// var oHead=oHtml.firstChild;
// var oHead=oHtml.childNodes[0];
var oHead=oHtml.childNodes.item(0);
var oBody=oHtml.childNodes[1];
// var oBody=oHtml.childNodes[1];
// console.log(oHead.parentNode == oHtml);
// console.log(oHtml.childNodes.item(0));
// console.log(oHtml.childNodes.item(2));
// console.log(oHtml.childNodes[0]);
console.log(oBody.previousSibling==oHead);
</script>
</head>
<body>
<p>文本叶子节点</p>
</body>
</html>
