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="Scenario_Type" />
  </query-continue>
  <query>
    <pages>
      <page ns="10" title="Template:Documentation" missing="" />
      <page pageid="174" ns="10" title="Template:Font color" />
      <page pageid="835" ns="10" title="Template:Scenario Task" />
      <page pageid="849" ns="10" title="Template:Scenario Task Parents" />
      <page pageid="1764" ns="10" title="Template:Scenario Task Translation" />
      <page pageid="856" ns="10" title="Template:Scenario Tool" />
      <page pageid="1813" ns="10" title="Template:Scenario Tool Translation" />
      <page pageid="1812" ns="10" title="Template:Scenario Tool Translation Action" />
      <page pageid="1778" ns="10" title="Template:Scenario Translation Action" />
      <page pageid="1777" ns="10" title="Template:Scenario Translations" />
    </pages>
  </query>
</api>