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>
    <allfileusages gafcontinue="Graf.PNG|83" />
  </query-continue>
  <query>
    <pages>
      <page pageid="19" ns="0" title="Předávací protokol" />
      <page pageid="24" ns="0" title="Záznamy STK" />
      <page pageid="25" ns="0" title="Instalační galerie" />
      <page pageid="27" ns="0" title="Nové hlášení poruchy" />
      <page pageid="28" ns="0" title="Hlášené poruchy" />
      <page pageid="51" ns="0" title="Deaktivace GCOMu" />
      <page pageid="69" ns="0" title="Denní report" />
      <page pageid="83" ns="0" title="Sumační data" />
    </pages>
  </query>
</api>