You are looking at the HTML representation of the XML format.
HTML is good for debugging, but probably is not suitable for your application.
See complete documentation, or API help for more information. 
<?xml version="1.0"?>
<api>
  <query>
    <allcategories>
      <c size="0" pages="0" files="0" subcats="0" xml:space="preserve">All articles needing additional references</c>
      <c size="5" pages="5" files="0" subcats="0" xml:space="preserve">Article message boxes</c>
      <c size="0" pages="0" files="0" subcats="0" xml:space="preserve">Articles needing additional references</c>
      <c size="1" pages="1" files="0" subcats="0" xml:space="preserve">Exclude in print</c>
      <c size="1" pages="1" files="0" subcats="0" xml:space="preserve">Template documentation</c>
      <c size="1" pages="1" files="0" subcats="0" xml:space="preserve">Wikipedia metatemplates</c>
      <c size="17" pages="17" files="0" subcats="0" xml:space="preserve">Wikipedia pages with incorrect protection templates</c>
      <c size="16" pages="16" files="0" subcats="0" xml:space="preserve">Wikipedia protected templates</c>
    </allcategories>
  </query>
</api>