You are looking at the HTML representation of the XML format.
HTML is good for debugging, but is unsuitable for application use.
Specify the format parameter to change the output format.
To see the non HTML representation of the XML format, set format=xml.
See the complete documentation, or API help for more information. 
<?xml version="1.0"?>
<api>
  <query-continue>
    <allfileusages gafcontinue="InsertSelectLock.png|45" />
  </query-continue>
  <query>
    <pages>
      <page pageid="17" ns="0" title="Mysql 高性能笔记" />
      <page pageid="22" ns="0" title="WIKI教程" />
      <page pageid="44" ns="0" title="高性能MySQL笔记（上）" />
      <page pageid="45" ns="0" title="高性能MySQL笔记（下）" />
      <page pageid="84" ns="0" title="图解HTTP笔记" />
    </pages>
  </query>
</api>