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="Not_selected_tab|140" />
  </query-continue>
  <query>
    <pages>
      <page pageid="1" ns="0" title="Huvudsida" />
      <page pageid="4" ns="0" title="1.1 Om tal" />
      <page pageid="7" ns="0" title="1.1 Övningar om tal" />
      <page pageid="11" ns="0" title="1.2 Räkneordning" />
      <page pageid="14" ns="0" title="1.2 Övningar till Räkneordning" />
      <page pageid="80" ns="0" title="Ekvationer" />
      <page pageid="81" ns="0" title="Övningar till Ekvationer" />
      <page pageid="105" ns="0" title="1.1 Polynom" />
      <page pageid="106" ns="0" title="1.1 Övningar till Polynom" />
      <page pageid="136" ns="0" title="1.3 Polynom i faktorform" />
    </pages>
  </query>
</api>