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="Main_other" />
  </query-continue>
  <query>
    <pages>
      <page ns="10" title="Template:Case preserving encode" missing="" />
      <page ns="10" title="Template:Documentation/docspace" 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 ns="10" title="Template:Documentation/template page" missing="" />
      <page pageid="829" ns="10" title="Template:Documentation" />
      <page pageid="828" ns="10" title="Template:Error" />
      <page pageid="826" ns="10" title="Template:ISO 639 name" />
      <page pageid="827" ns="10" title="Template:ISO 639 name undefined" />
    </pages>
  </query>
</api>