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="Notexists|16" />
  </query-continue>
  <query>
    <pages>
      <page pageid="16" ns="0" title="Gdeliveryd ProtocolType" />
      <page pageid="17" ns="0" title="Gdeliveryd CallID" />
      <page pageid="606" ns="8" title="MediaWiki:Common.css" />
      <page pageid="1238" ns="2" title="Участник:DesmondHume" />
      <page pageid="1248" ns="2" title="Участник:DesmondHumeBot1" />
      <page pageid="3986" ns="0" title="Main Page" />
      <page pageid="4006" ns="0" title="Extender Task Manager" />
      <page pageid="4011" ns="10" title="Шаблон:User pl-3" />
      <page pageid="4018" ns="10" title="Шаблон:В планах" />
      <page pageid="4241" ns="0" title="Test" />
    </pages>
  </query>
</api>