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="Fußballspiel|673" />
  </query-continue>
  <query>
    <pages>
      <page pageid="115" ns="10" title="Vorlage:Infobox Fußballspieler" />
      <page pageid="490" ns="10" title="Vorlage:Infobox Stadion" />
      <page pageid="491" ns="0" title="Billetal-Kampfbahn" />
      <page pageid="609" ns="0" title="Stadion an der Ostsee" />
      <page pageid="637" ns="10" title="Vorlage:Fußballspiel" />
      <page pageid="639" ns="0" title="Deutscher Pokal 2012/2013" />
      <page pageid="642" ns="0" title="Deutscher Supercup 2012" />
      <page pageid="1201" ns="0" title="Pogo Park" />
      <page pageid="1203" ns="0" title="Pogo Cottage" />
      <page pageid="1295" ns="0" title="Estadi caldera de les bruixes" />
    </pages>
  </query>
</api>