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 ns="6" title="File:2013 Porsche 918 Spyder development mule in Monaco.jpg" missing="" contentmodel="wikitext" pagelanguage="en" />
      <page ns="6" title="File:Koenigsegg Agera R.jpg" missing="" contentmodel="wikitext" pagelanguage="en" />
      <page ns="6" title="File:Mercedes Benz AMG SLS Black.jpg" missing="" contentmodel="wikitext" pagelanguage="en" />
    </pages>
  </query>
</api>