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>
    <backlinks>
      <bl pageid="857" ns="0" title="Dynamic Lighting Examples" />
      <bl pageid="1362" ns="0" title="メインページ(日本語)" />
      <bl pageid="2708" ns="0" title="Advanced Dungeons and Dragons" />
      <bl pageid="2711" ns="0" title="ADnD 2nd Edition Character sheet" />
      <bl pageid="2735" ns="10" title="Template:Compact toc" />
      <bl pageid="2736" ns="10" title="Template:Compact toc/doc" />
      <bl pageid="3157" ns="0" title="ADnD 2nd Edition Character sheet Simplified" />
    </backlinks>
  </query>
</api>