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="ColorBackground|137" />
  </query-continue>
  <query>
    <pages>
      <page pageid="1" ns="0" title="Portada" />
      <page pageid="8" ns="10" title="Plantilla:Boxlayout1" />
      <page pageid="24" ns="10" title="Plantilla:Niveles de Edificios" />
      <page pageid="132" ns="0" title="Hadas del Fuego" />
      <page pageid="133" ns="0" title="Centauro Histérica" />
      <page pageid="134" ns="0" title="Centauros Salvajes" />
      <page pageid="135" ns="0" title="Semigigantes Cantores" />
      <page pageid="220" ns="4" title="Xhodon:Árbol de categorías" />
      <page pageid="1493" ns="0" title="Página principal" />
      <page pageid="1708" ns="0" title="Módulos de Mantenimiento" />
    </pages>
  </query>
</api>