<s1>
  <s11>
    <s111/>
    <s112/>
    <s113/>
  </s11>
  <s12>
    <s121>
      <s1211/>
      <s1212/>
    </s121>
    <s122>
      <s1221/>
      <s1222/>
    </s122>
  </s12>
</s1>
