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>
    <allredirects>
      <r ns="0" title="Op:スレイヤーズVSオーフェン" />
      <r ns="0" title="Op:魔術士オーフェンはぐれ旅" />
      <r ns="0" title="Op:魔術士オーフェンまわり道" />
      <r ns="0" title="Op:魔術士オーフェン・無謀編" />
      <r ns="0" title="イラストレーターの一覧" />
    </allredirects>
  </query>
</api>