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>
    <allfileusages>
      <f fromid="68" ns="6" title="檔案:Glory Day celebration of the Poumai Naga.jpg" />
      <f fromid="373" ns="6" title="檔案:Http://www.tea909.com/forum.php" />
      <f fromid="1" ns="6" title="檔案:Logo 80px.jpg" />
      <f fromid="215" ns="6" title="檔案:Logo 80px.jpg" />
      <f fromid="6" ns="6" title="檔案:P1J010.jpg" />
      <f fromid="348" ns="6" title="檔案:PIC61.jpg" />
      <f fromid="5" ns="6" title="檔案:Twm-001.jpg" />
    </allfileusages>
  </query>
</api>