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="5E_OGL_Sheet_Bio_Header.png" />
  </query-continue>
  <query>
    <pages>
      <page pageid="2579" ns="6" title="File:10 Emote Non-Roll Template Roll.png" />
      <page pageid="3637" ns="6" title="File:13th-Age-Legacy.jpg" />
      <page pageid="3763" ns="6" title="File:13th Age Official.png" />
      <page pageid="2571" ns="6" title="File:1 Character Journal Tabs.png" />
      <page pageid="3351" ns="6" title="File:3D dice color.jpg" />
      <page pageid="2666" ns="6" title="File:5E Compendium Source Tags.png" />
      <page pageid="2533" ns="6" title="File:5E OGL PC Core Guide.jpg" />
      <page pageid="2529" ns="6" title="File:5E OGL Sheet AC Init Speed.png" />
      <page pageid="2535" ns="6" title="File:5E OGL Sheet Attacks And Spellcasting.png" />
      <page pageid="2523" ns="6" title="File:5E OGL Sheet Attribute Block.jpg" />
    </pages>
  </query>
</api>