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>
    <allpages apcontinue="Cambiar_el_chromedriver_para_GXtest" />
  </query-continue>
  <query>
    <allpages>
      <p pageid="253" ns="0" title="Basic Configurations in GXtest Manager" />
      <p pageid="321" ns="0" title="Basics to the installation" />
      <p pageid="273" ns="0" title="Beneficios de GXtest" />
      <p pageid="539" ns="0" title="Best Practices automating with GXtest" />
      <p pageid="538" ns="0" title="Buenas Prácticas de Automatización con GXtest" />
      <p pageid="282" ns="0" title="Bugs Conocidos GXtest" />
      <p pageid="838" ns="0" title="Building JMeter scripts with GXtest" />
      <p pageid="836" ns="0" title="Building OpenSTA scripts with GXtest" />
      <p pageid="267" ns="0" title="Builds de GXtest 1.1 Beta" />
      <p pageid="320" ns="0" title="Básicas para la instalación" />
    </allpages>
  </query>
</api>