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="Box|2284" />
  </query-continue>
  <query>
    <pages>
      <page pageid="255" ns="10" title="Šablona:Zkontrolováno" />
      <page pageid="256" ns="10" title="Šablona:Box" />
      <page pageid="257" ns="10" title="Šablona:Podšablona" />
      <page pageid="536" ns="2" title="Uživatel:Admin/Pískoviště" />
      <page pageid="896" ns="10" title="Šablona:Zkontrolováno/dokumentace" />
      <page pageid="900" ns="10" title="Šablona:Dokumentace" />
      <page pageid="1078" ns="10" title="Šablona:Neměňte tento řádek" />
      <page pageid="1285" ns="0" title="The origins of English" />
      <page pageid="1994" ns="0" title="Bradfordův zákon" />
      <page pageid="2145" ns="0" title="Etika informačního specialisty" />
    </pages>
  </query>
</api>