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="BUR_rocket.jpg|3705" />
  </query-continue>
  <query>
    <allfileusages>
      <f fromid="3781" ns="6" title="File:BM59 bayo.jpg" />
      <f fromid="3817" ns="6" title="File:BM59 bayo.jpg" />
      <f fromid="30" ns="6" title="File:BMS Milcam HB.jpg" />
      <f fromid="755" ns="6" title="File:BMS Milcam HB.jpg" />
      <f fromid="2669" ns="6" title="File:BRR crossbow.jpg" />
      <f fromid="2856" ns="6" title="File:BRR crossbow.jpg" />
      <f fromid="30" ns="6" title="File:BSA Lewis gun.JPG" />
      <f fromid="676" ns="6" title="File:BSA Lewis gun.JPG" />
      <f fromid="699" ns="6" title="File:BSA Welrod Mk I.jpg" />
      <f fromid="5834" ns="6" title="File:BSA Welrod Mk I.jpg" />
    </allfileusages>
  </query>
</api>