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="Behavior_1_3_result.PNG" />
  </query-continue>
  <query>
    <pages>
      <page pageid="1646" ns="6" title="File:BON token text.png" />
      <page pageid="2065" ns="6" title="File:Basic class menu.PNG" />
      <page pageid="2067" ns="6" title="File:Basic cluster menu.PNG" />
      <page pageid="2064" ns="6" title="File:Basic editor menu.PNG" />
      <page pageid="2066" ns="6" title="File:Basic feature menu.PNG" />
      <page pageid="2611" ns="6" title="File:Behavior 1 1 pasted at.PNG" />
      <page pageid="2613" ns="6" title="File:Behavior 1 1 result.PNG" />
      <page pageid="2614" ns="6" title="File:Behavior 1 2 pasted at.PNG" />
      <page pageid="2615" ns="6" title="File:Behavior 1 2 result.PNG" />
      <page pageid="2616" ns="6" title="File:Behavior 1 3 pasted at.PNG" />
    </pages>
  </query>
</api>