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>
    <allcategories>
      <c size="2" pages="2" files="0" subcats="0" xml:space="preserve">Admins and Mods</c>
      <c size="1" pages="1" files="0" subcats="0" xml:space="preserve">Animes</c>
      <c size="5" pages="5" files="0" subcats="0" xml:space="preserve">Articles containing spoilers</c>
      <c size="27" pages="26" files="0" subcats="1" xml:space="preserve">Articles in need of expansion</c>
      <c size="1" pages="1" files="0" subcats="0" xml:space="preserve">Articles in need of visual examples</c>
      <c size="3" pages="3" files="0" subcats="0" xml:space="preserve">Articles with sections in need of expansion</c>
      <c size="4" pages="4" files="0" subcats="0" xml:space="preserve">Characters</c>
      <c size="2" pages="2" files="0" subcats="0" xml:space="preserve">Characters with a Lolikon Complex</c>
      <c size="5" pages="1" files="0" subcats="4" xml:space="preserve">Content</c>
      <c size="2" pages="2" files="0" subcats="0" xml:space="preserve">Disambiguation pages</c>
    </allcategories>
  </query>
  <query-continue>
    <allcategories accontinue="Doujinshi" />
  </query-continue>
</api>