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>
    <alltransclusions gatcontinue="Step_by_Step" />
  </query-continue>
  <query>
    <pages>
      <page ns="10" title="Modèle:En" missing="" />
      <page ns="10" title="Modèle:Fr" missing="" />
      <page pageid="5" ns="10" title="Modèle:Box Attention" />
      <page pageid="3" ns="10" title="Modèle:Box Console" />
      <page pageid="15" ns="10" title="Modèle:Box Construction" />
      <page pageid="6" ns="10" title="Modèle:Box Information" />
      <page pageid="13" ns="10" title="Modèle:Box Legislation" />
      <page pageid="7" ns="10" title="Modèle:Box Remarque" />
      <page pageid="42" ns="10" title="Modèle:Linksys Products" />
      <page pageid="397" ns="10" title="Modèle:Serveur de Messagerie" />
    </pages>
  </query>
</api>