DOMDocument:saveXML 返回值替空字符串

<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 />