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>
    <alllinks galcontinue="Buenas_Prácticas_de_Automatización_con_GXtest|539" />
  </query-continue>
  <query>
    <pages>
      <page pageid="208" ns="0" title="Primeras Configuraciones en GXtest Manager" />
      <page pageid="251" ns="0" title="GXtest Manager Tutorial" />
      <page pageid="252" ns="0" title="Starting out with GXtest Manager" />
      <page pageid="253" ns="0" title="Basic Configurations in GXtest Manager" />
      <page pageid="320" ns="0" title="Básicas para la instalación" />
      <page pageid="321" ns="0" title="Basics to the installation" />
      <page pageid="538" ns="0" title="Buenas Prácticas de Automatización con GXtest" />
      <page pageid="539" ns="0" title="Best Practices automating with GXtest" />
      <page pageid="815" ns="0" title="GXtest Manager の基本構成" />
    </pages>
  </query>
</api>