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>
    <alltransclusions gatcontinue="Documentation/template_page" />
  </query-continue>
  <query>
    <pages>
      <page ns="10" title="Template:Documentation" missing="" />
      <page ns="10" title="Template:Documentation/docspace" missing="" />
      <page ns="10" title="Template:Documentation/end box" missing="" />
      <page ns="10" title="Template:Documentation/end box2" missing="" />
      <page ns="10" title="Template:Documentation/start box" missing="" />
      <page ns="10" title="Template:Documentation/start box2" missing="" />
      <page pageid="30" ns="10" title="Template:Cat handler" />
      <page pageid="31" ns="10" title="Template:Category handler" />
      <page pageid="32" ns="10" title="Template:Category handler/blacklist" />
      <page pageid="33" ns="10" title="Template:Category handler/numbered" />
    </pages>
  </query>
</api>