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="Admin-Export-element-icon.png" />
  </query-continue>
  <query>
    <pages>
      <page pageid="1847" ns="6" title="File:20161810 BioUML platform.pdf" />
      <page pageid="1227" ns="6" title="File:Accept2viewparts icon.png" />
      <page pageid="493" ns="6" title="File:Access via subscription centre.png" />
      <page pageid="1228" ns="6" title="File:Add2clipboard icon.png" />
      <page pageid="1224" ns="6" title="File:Add2docpane icon.png" />
      <page pageid="1225" ns="6" title="File:Add2newdia icon.png" />
      <page pageid="1221" ns="6" title="File:Add element icon.png" />
      <page pageid="1273" ns="6" title="File:Adjusting diagram layout.png" />
      <page pageid="1247" ns="6" title="File:Adjusting table.png" />
      <page pageid="2382" ns="6" title="File:Admin-Check-quotas-icon.png" />
    </pages>
  </query>
</api>