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="Biseptol.jpg|2405" />
  </query-continue>
  <query>
    <pages>
      <page pageid="1140" ns="0" title="Drukuj FV w FR3" />
      <page pageid="1208" ns="0" title="MotławaWiki:Opis szablonów" />
      <page pageid="1505" ns="0" title="Błąd 42000PROCEDURE ... does not exist" />
      <page pageid="1507" ns="10" title="Szablon:ShowError" />
      <page pageid="1625" ns="0" title="I/O Error 32" />
      <page pageid="2003" ns="0" title="Wydruk polecenia księgowania (Bank)" />
      <page pageid="2005" ns="0" title="Wydruk polecenia księgowania - waluta (Bank)" />
      <page pageid="2186" ns="0" title="Duplicate entry" />
      <page pageid="2368" ns="0" title="HELP Z06 Badacz" />
      <page pageid="2402" ns="0" title="HELP BrakUprWybOper" />
    </pages>
  </query>
</api>