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="Chess_Kd44.png|9" />
  </query-continue>
  <query>
    <pages>
      <page pageid="6" ns="0" title="Pedone alla Biggs" />
      <page pageid="8" ns="10" title="Template:Chess diagram" />
      <page pageid="9" ns="0" title="Gergo scacchistico" />
      <page pageid="161" ns="0" title="Come importare i certificati di sicurezza" />
    </pages>
  </query>
</api>