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="IOS_logo.png" />
  </query-continue>
  <query>
    <pages>
      <page ns="6" title="File:Database.png" missing="" />
      <page pageid="39" ns="6" title="File:Book.png" />
      <page pageid="17" ns="6" title="File:Check.png" />
      <page pageid="22" ns="6" title="File:Constraints.png" />
      <page pageid="119" ns="6" title="File:Dati di lavoro.png" />
      <page pageid="89" ns="6" title="File:Desktop.png" />
      <page pageid="122" ns="6" title="File:Desktop login.png" />
      <page pageid="143" ns="6" title="File:Desktop r professore sinottico.png" />
      <page pageid="164" ns="6" title="File:Elenco comuni italiani 30 giugno 2013.txt" />
      <page pageid="16" ns="6" title="File:Faq.png" />
    </pages>
  </query>
</api>