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="Groups_edit_members.png" />
  </query-continue>
  <query>
    <pages>
      <page ns="6" title="File:Forms-index.jpg" missing="" />
      <page pageid="39" ns="6" title="File:Collections explained.png" />
      <page pageid="56" ns="6" title="File:Cross.gif" />
      <page pageid="44" ns="6" title="File:Edit.gif" />
      <page pageid="45" ns="6" title="File:Email.gif" />
      <page pageid="21" ns="6" title="File:Forms edit criteria.png" />
      <page pageid="52" ns="6" title="File:Forms ex criterion assess.png" />
      <page pageid="61" ns="6" title="File:Forms list.png" />
      <page pageid="53" ns="6" title="File:Forms toolbar.png" />
      <page pageid="47" ns="6" title="File:Group marks.gif" />
    </pages>
  </query>
</api>