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="Dzien.png|52" />
  </query-continue>
  <query>
    <pages>
      <page pageid="25" ns="0" title="Dodawanie oferty" />
      <page pageid="26" ns="0" title="Edycja oferty" />
      <page pageid="30" ns="0" title="Kopiowanie oferty" />
      <page pageid="54" ns="0" title="Wydruki" />
      <page pageid="56" ns="0" title="Dodawanie agenta" />
      <page pageid="61" ns="0" title="Edycja lokalizacji" />
      <page pageid="323" ns="0" title="Aktualizacja-listopad-2014" />
      <page pageid="389" ns="0" title="Aktualizacja-luty-2016" />
    </pages>
  </query>
</api>