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>
    <allfileusages gafcontinue="BayG1866.TIF|638" />
  </query-continue>
  <query>
    <pages>
      <page pageid="622" ns="0" title="Arnold Baader" />
      <page pageid="624" ns="0" title="Johann Jakob Baader" />
      <page pageid="627" ns="0" title="Johann Jakob Balmer" />
      <page pageid="631" ns="0" title="Bruno Ernst Otto Balscheit" />
      <page pageid="633" ns="0" title="Benedikt Banga" />
      <page pageid="637" ns="0" title="Ernst Baumann" />
      <page pageid="1653" ns="0" title="Walter Ballmer" />
      <page pageid="1968" ns="0" title="Serena Bangerter-Buser" />
      <page pageid="1999" ns="0" title="Bernhard Baumgartner" />
      <page pageid="2192" ns="0" title="Lorenz Balmer" />
    </pages>
  </query>
</api>