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>
    <pages>
      <page pageid="149" ns="0" title="Center" />
      <page pageid="116" ns="0" title="Fully invariant subgroup" />
      <page pageid="187" ns="0" title="Logical graph" />
      <page pageid="6" ns="0" title="Normal" />
      <page pageid="45" ns="0" title="Normal field extension" />
      <page pageid="9" ns="0" title="Normal subgroup" />
      <page pageid="344" ns="0" title="Semeiotic" />
      <page pageid="118" ns="0" title="Subnormal subgroup" />
    </pages>
  </query>
</api>