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="9000_Sécurité_et_prévention" />
  </query-continue>
  <query>
    <allcategories>
      <c size="3" pages="3" files="0" subcats="0" xml:space="preserve">1000 Administration</c>
      <c size="1" pages="1" files="0" subcats="0" xml:space="preserve">11000 Enseignement</c>
      <c size="2" pages="2" files="0" subcats="0" xml:space="preserve">13000 Vie étudiante</c>
      <c size="2" pages="2" files="0" subcats="0" xml:space="preserve">3000 Ressources humaines</c>
      <c size="4" pages="4" files="0" subcats="0" xml:space="preserve">4000 Ressources financières</c>
      <c size="2" pages="2" files="0" subcats="0" xml:space="preserve">5000 Ressources immobilières</c>
      <c size="1" pages="1" files="0" subcats="0" xml:space="preserve">5200 Espaces intérieurs</c>
      <c size="1" pages="1" files="0" subcats="0" xml:space="preserve">6000 Ressources mobilières, équipements</c>
      <c size="1" pages="1" files="0" subcats="0" xml:space="preserve">7000 Ressources infomationnelles</c>
      <c size="2" pages="2" files="0" subcats="0" xml:space="preserve">8000 Informatique et télécommunications</c>
    </allcategories>
  </query>
</api>