DOMDocument::saveXML 返回值为空字符串

PHP saveXML PHP手册中的的实例：

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

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!

回复讨论(解决方案)

请在文本方式下查看

Saving all the document:string(72) ""

明白了，Thanks!