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="3" pages="3" files="0" subcats="0" xml:space="preserve">Acronyms</c>
      <c size="5" pages="5" files="0" subcats="0" xml:space="preserve">Articles lacking sources</c>
      <c size="3" pages="3" files="0" subcats="0" xml:space="preserve">Articles with unsourced statements</c>
      <c size="1" pages="1" files="0" subcats="0" xml:space="preserve">Computational fluid dynamics</c>
      <c size="0" pages="0" files="0" subcats="0" xml:space="preserve">Computer-aided design software</c>
      <c size="0" pages="0" files="0" subcats="0" xml:space="preserve">Computer-aided engineering software</c>
      <c size="0" pages="0" files="0" subcats="0" xml:space="preserve">Computer-aided engineering software for Linux</c>
      <c size="0" pages="0" files="0" subcats="0" xml:space="preserve">Computer system optimization software</c>
      <c size="0" pages="0" files="0" subcats="0" xml:space="preserve">Continuum mechanics</c>
      <c size="20" pages="20" files="0" subcats="0" xml:space="preserve">Dimensionless parameters</c>
    </allcategories>
  </query>
  <query-continue>
    <allcategories acfrom="Equations" />
  </query-continue>
</api>