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>
    <alltransclusions gatcontinue="Idiomas|73" />
  </query-continue>
  <query>
    <pages>
      <page pageid="4" ns="0" title="Manual de Usuario de GXtest Designer 1.0" />
      <page pageid="6" ns="0" title="Tutorial de GXtest Designer" />
      <page pageid="38" ns="0" title="Metodología para usar GXtest" />
      <page pageid="39" ns="0" title="Quick Start" />
      <page pageid="42" ns="0" title="Overview" />
      <page pageid="44" ns="0" title="¿Por qué Automatizar?" />
      <page pageid="45" ns="0" title="Request Feature GXtest Designer" />
      <page pageid="50" ns="0" title="Manual de Usuario de GXtest Recorder" />
      <page pageid="63" ns="0" title="FAQs GXtest Designer" />
      <page pageid="65" ns="0" title="Cómo ajustar la Zona de Seguridad para el Sitio a Probar" />
    </pages>
  </query>
</api>