DOMDocument:saveXML 返回值替空字符串

DOMDocument::saveXML 返回值为空字符串
PHP手册中的的实例：

<br />        $doc = new DOMDocument('1.0');<br />	// we want a nice output<br />	$doc->formatOutput = true;<br /><br />	$root = $doc->createElement('book');<br />	$root = $doc->appendChild($root);<br /><br />	$title = $doc->createElement('title');<br />	$title = $root->appendChild($title);<br /><br />	$text = $doc->createTextNode('This is the title');<br />	$text = $title->appendChild($text);<br /><br />		<br />	echo "Saving all the document:\n";<br />	<br />	$xmlContent = $doc->saveXML();<br />	<br />	var_dump($xmlContent);<br />

打印出的结果是：
Saving all the document: string(72) " " 

为什么没有打印出完整的XML？请各位前辈指点，Thanks!

PHP saveXML

分享到：
------解决方案--------------------
请在文本方式下查看

Saving all the document:<br />string(72) "<?xml version="1.0"?><br /><book><br />  <title>This is the title</title><br /></book><br />"<br /><br />