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>
    <allfileusages gafcontinue="Munsu_will_on_mb.jpg|118" />
  </query-continue>
  <query>
    <pages>
      <page pageid="73" ns="10" title="Template:Documentation subpage" />
      <page pageid="74" ns="10" title="Template:Mbox" />
      <page pageid="76" ns="10" title="Template:Fmbox" />
      <page pageid="77" ns="10" title="Template:Ombox" />
      <page pageid="78" ns="10" title="Template:Ombox/core" />
      <page pageid="148" ns="0" title="Lord of Light" />
      <page pageid="308" ns="0" title="Concrete Mathematics" />
      <page pageid="325" ns="0" title="Information Theory, Inference, and Learning Algorithms" />
      <page pageid="543" ns="0" title="Everything is obvious" />
      <page pageid="590" ns="0" title="Gödel, Escher, Bach" />
    </pages>
  </query>
</api>