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>
    <allimages gaicontinue="2004Mayo-1.png" />
  </query-continue>
  <query>
    <pages>
      <page pageid="673" ns="6" title="File:10 133 148.pdf" />
      <page pageid="376" ns="6" title="File:13-05-22 CIERRE DE PROGRAMAS DE EDUCACIÓN CONTINUA.docx" />
      <page pageid="849" ns="6" title="File:2004Diciembre-1.png" />
      <page pageid="848" ns="6" title="File:2003Diciembre-17.png" />
      <page pageid="850" ns="6" title="File:2004Diciembre-18.png" />
      <page pageid="952" ns="6" title="File:0.Taller Modelos Lineales II.pdf" />
      <page pageid="1270" ns="6" title="File:0808.1375.pdf" />
      <page pageid="368" ns="6" title="File:13-04-24 CREACIÓN DE PROGRAMAS DE EDUCACIÓN CONTINUADA.docx" />
      <page pageid="1329" ns="6" title="File:1-s2.0-S0378437116000431-main.pdf" />
      <page pageid="370" ns="6" title="File:13-04-24 OFERTA Y APERTURA DE PROGRAMAS DE EDUCACIÓN CONTINUA.docx" />
    </pages>
  </query>
</api>