如何从这个xml中获取属性？(PHP)

$xmlString = '<bookstore>
  <book category="cooking">
    <title lang="en">Everyday Italian</title>
    <author>Giada De Laurentiis</author>
    <year>2005</year>
    <price>30.00</price>
  </book>
  <book category="children">
    <title lang="en">Harry Potter</title>
    <author>J.K. Rowling</author>
    <year>2005</year>
    <price>29.99</price>
  </book>
</bookstore>';

$xml = simplexml_load_string($xmlString);

// 获取第一个book节点的category属性
$category = $xml->book[0]['category'];
echo "Category: " . $category . "\n";

// 获取第二个book节点的title节点的lang属性
$lang = $xml->book[1]->title['lang'];
echo "Language: " . $lang . "\n";

Category: cooking
Language: en