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 />