<div><p>content</p></div>
innerHTML的内容包括:<p>content</p>
innerTEXT的内容包括:content
<div><span id='pre'></span><span id='next'></span></div>
<script type="text/javascript">
alert(document.getElementById("pre").nextSibling.tagName);//<span id='next'></span>
alert(document.getElementById("next").previousSibling.tagName);//<span id='pre'></span>
</script>