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="Cc-by_new_white.svg|1130" />
  </query-continue>
  <query>
    <allfileusages>
      <f fromid="116" ns="6" title="Файл:Bel zd.jpg" />
      <f fromid="390" ns="6" title="Файл:Best put table.jpg" />
      <f fromid="29" ns="6" title="Файл:Broom icon.svg" />
      <f fromid="34" ns="6" title="Файл:Broom icon.svg" />
      <f fromid="288" ns="6" title="Файл:Bulbgraph.png" />
      <f fromid="1113" ns="6" title="Файл:Bulbgraph.png" />
      <f fromid="251" ns="6" title="Файл:Button sig.png" />
      <f fromid="261" ns="6" title="Файл:Button sig.png" />
      <f fromid="938" ns="6" title="Файл:Button sig.png" />
      <f fromid="1130" ns="6" title="Файл:CC some rights reserved.svg" />
    </allfileusages>
  </query>
</api>