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 afcontinue="Boxed_East_arrow.svg|263" />
  </query-continue>
  <query>
    <allfileusages>
      <f ns="6" title="Soubor:Bandiera del Regno di Sicilia 4.svg" />
      <f ns="6" title="Soubor:Bandiera del Regno di Sicilia 4.svg" />
      <f ns="6" title="Soubor:Banín.jpg" />
      <f ns="6" title="Soubor:Banín CoA CZ.svg" />
      <f ns="6" title="Soubor:Bishop Mathias Franz Count of Chorinsky Baron of Ledske.jpg" />
      <f ns="6" title="Soubor:Blue pog.svg" />
      <f ns="6" title="Soubor:Blue pog.svg" />
      <f ns="6" title="Soubor:Bohemia1590 1609.jpg" />
      <f ns="6" title="Soubor:Bohumil Hrabal by Kubik 1994 01.jpg" />
      <f ns="6" title="Soubor:Bolek Polivka.jpg" />
    </allfileusages>
  </query>
</api>