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>
    <allcategories accontinue="Geography" />
  </query-continue>
  <query>
    <allcategories>
      <c size="3" pages="3" files="0" subcats="0" xml:space="preserve">Advice</c>
      <c size="0" pages="0" files="0" subcats="0" xml:space="preserve">Article Feedback Blacklist</c>
      <c size="3" pages="3" files="0" subcats="0" xml:space="preserve">Article message boxes</c>
      <c size="0" pages="0" files="0" subcats="0" xml:space="preserve">Category namespace templates</c>
      <c size="7" pages="0" files="0" subcats="7" xml:space="preserve">Contents</c>
      <c size="192" pages="192" files="0" subcats="0" xml:space="preserve">Country</c>
      <c size="1" pages="1" files="0" subcats="0" xml:space="preserve">Country pieces de rechanges du carburateur cylaindre moteur puissance apprélia GFOX XR-32011 à Moto Gillera Runner Made in itali</c>
      <c size="1" pages="1" files="0" subcats="0" xml:space="preserve">Europe</c>
      <c size="0" pages="0" files="0" subcats="0" xml:space="preserve">Exclude in print</c>
      <c size="1" pages="1" files="0" subcats="0" xml:space="preserve">Ferry Crossings</c>
    </allcategories>
  </query>
</api>