帮助在php中使用xmlreader读取嵌套的xml

<root>
  <thing>
    <specs>
      <spec1 />
      <spec3 />
      <spec2 />
    </specs>
    <details />
    <more_info>
      <info1 />
      <info2 />
    </more_info>
  </thing>
</root>
<root>
  <thing>
    <specs>
      <spec1 />