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>
    <pages>
      <page pageid="1" ns="0" title="Página principal" contentmodel="wikitext" pagelanguage="es" touched="2015-09-14T22:48:14Z" lastrevid="5926" counter="29888" length="1577" />
      <page pageid="12" ns="0" title="Lista de módulos" contentmodel="wikitext" pagelanguage="es" touched="2015-09-01T16:51:17Z" lastrevid="1279" counter="1363" length="117" />
      <page pageid="173" ns="0" title="Glosario" contentmodel="wikitext" pagelanguage="es" touched="2014-06-13T17:19:24Z" lastrevid="224" counter="153" length="323" new="" />
      <page pageid="205" ns="0" title="Barra de herramientas" contentmodel="wikitext" pagelanguage="es" touched="2017-03-29T00:51:06Z" lastrevid="5980" counter="2252" length="1643" />
      <page pageid="212" ns="0" title="Dispositivo" contentmodel="wikitext" pagelanguage="es" touched="2017-03-29T01:05:04Z" lastrevid="5983" counter="3563" length="2066" />
      <page pageid="388" ns="14" title="Categoría:Módulos" contentmodel="wikitext" pagelanguage="es" touched="2015-09-01T16:51:17Z" lastrevid="1914" counter="2536" length="126" />
      <page pageid="559" ns="0" title="Composición histórica (CAC)" contentmodel="wikitext" pagelanguage="es" touched="2015-09-01T16:51:17Z" lastrevid="2560" counter="1491" length="2350" />
      <page pageid="563" ns="0" title="Composición histórica (CAP)" contentmodel="wikitext" pagelanguage="es" touched="2015-09-01T16:51:17Z" lastrevid="2559" counter="1219" length="2463" />
      <page pageid="633" ns="0" title="Pendientes (CAC)" contentmodel="wikitext" pagelanguage="es" touched="2015-09-01T16:51:17Z" lastrevid="2252" counter="975" length="1612" />
      <page pageid="634" ns="0" title="Pendientes (CAP)" contentmodel="wikitext" pagelanguage="es" touched="2015-09-01T16:51:17Z" lastrevid="2253" counter="599" length="1166" new="" />
    </pages>
  </query>
</api>