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>
    <allredirects garcontinue="Helsingin_matematiikkalukio,_kulkuyhteydet" />
  </query-continue>
  <query>
    <pages>
      <page pageid="1543" ns="0" title="Biodiversity equals ethanol" />
      <page pageid="1558" ns="0" title="Bridge-sijoituksia" />
      <page pageid="1869" ns="0" title="Carita Eklund" />
      <page pageid="2295" ns="0" title="Ella Anttila" />
      <page pageid="1472" ns="0" title="Esa Vesalainen" />
      <page pageid="1" ns="0" title="Etusivu" />
      <page pageid="1468" ns="0" title="Funktioteoria" />
      <page pageid="2476" ns="0" title="Hanna Lempiäinen" />
      <page pageid="1937" ns="0" title="Heikki Salko" />
      <page pageid="1453" ns="0" title="Helsingin matematiikkalukio" />
    </pages>
  </query>
</api>