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="Benjamin_Constant.jpg|4654" />
  </query-continue>
  <query>
    <pages>
      <page pageid="738" ns="0" title="El Basilisco" />
      <page pageid="1470" ns="0" title="Jaime Luciano Balmes" />
      <page pageid="1746" ns="0" title="Miguel Bakunin" />
      <page pageid="2796" ns="0" title="César Beccaria" />
      <page pageid="3109" ns="0" title="Jaime Beattie" />
      <page pageid="3929" ns="0" title="Jesús de Nazaret" />
      <page pageid="4342" ns="0" title="Rolando Barthes" />
    </pages>
  </query>
</api>