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>
    <alllinks galcontinue="Biomolecular_Feedback_Systems" />
  </query-continue>
  <query>
    <pages>
      <page ns="0" title="Balance system" missing="" />
      <page ns="0" title="Biological circuits" missing="" />
      <page pageid="2345" ns="0" title="BFS" />
      <page pageid="2392" ns="0" title="BFS:Archived news" />
      <page pageid="1709" ns="0" title="Balance systems" />
      <page pageid="1548" ns="0" title="Ball and Beam Introduction" />
      <page pageid="1710" ns="0" title="Ball and Beam Simulation" />
      <page pageid="1337" ns="0" title="Ball and beam system" />
      <page pageid="1317" ns="0" title="Bibliography" />
      <page pageid="1719" ns="0" title="Bicycle dynamics" />
    </pages>
  </query>
</api>