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="Capturaa.PNG|59" />
  </query-continue>
  <query>
    <pages>
      <page pageid="266" ns="0" title="¿Que significa que Meteoclimatic esté acogido a Creative Commons?" />
      <page pageid="450" ns="0" title="Bird Spikes" />
      <page pageid="503" ns="0" title="WDconsole RPI" />
      <page pageid="663" ns="0" title="Configuración Cumulus MX para Meteoclimatic" />
    </pages>
  </query>
</api>