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="Carl_Bloch_Sermon_on_Mount.jpg" />
  </query-continue>
  <query>
    <pages>
      <page ns="6" title="File:B.B. King in 2009.jpg" missing="" />
      <page ns="6" title="File:Bach-Bild von &#039;Gebel&#039;, vor 1798.jpg" missing="" />
      <page ns="6" title="File:Big Ben Clock London UK.jpg" missing="" />
      <page ns="6" title="File:Bloch-SermonOnTheMount.jpg" missing="" />
      <page ns="6" title="File:Bobby Fischer smiling 1972.jpg" missing="" />
      <page ns="6" title="File:Branches of Christianity.jpg" missing="" />
      <page ns="6" title="File:Byzantine art.jpg" missing="" />
      <page ns="6" title="File:CIF San Diego Championship 2007.jpg" missing="" />
      <page pageid="285" ns="6" title="File:Bill to withdraw jurisdiction re draft.png" />
      <page pageid="417" ns="6" title="File:Capitol Hill Club event for Phyllis 2017.jpg" />
    </pages>
  </query>
</api>