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>
    <allredirects garcontinue="Back_to_Skool|11637" />
  </query-continue>
  <query>
    <pages>
      <page pageid="4126" ns="0" title="Back to the Future" />
      <page pageid="4127" ns="0" title="BTTF" />
      <page pageid="4130" ns="0" title="Back To The Future 2" />
      <page pageid="4131" ns="0" title="Back To The Future II" />
      <page pageid="4132" ns="0" title="BTTF II" />
      <page pageid="4133" ns="0" title="BTTF 2" />
      <page pageid="4134" ns="0" title="Back to the Future Part III" />
      <page pageid="4135" ns="0" title="Back To The Future 3" />
      <page pageid="4136" ns="0" title="BTTF III" />
      <page pageid="4137" ns="0" title="BTTF 3" />
    </pages>
  </query>
</api>