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>
    <allimages gaicontinue="Bathroom_mold.gif" />
  </query-continue>
  <query>
    <pages>
      <page pageid="221" ns="6" title="File:A professional man inspecting for allergies.gif" />
      <page pageid="253" ns="6" title="File:Algae and pond scum.jpg" />
      <page pageid="252" ns="6" title="File:Algae causing oxygen demand.jpg" />
      <page pageid="264" ns="6" title="File:Algae in a pond.gif" />
      <page pageid="212" ns="6" title="File:Anaerobic digestion process.gif" />
      <page pageid="213" ns="6" title="File:Anaerobic digestion process family.gif" />
      <page pageid="249" ns="6" title="File:Back hoe required to did out a septic tank drainfield.gif" />
      <page pageid="189" ns="6" title="File:Basement mold.gif" />
      <page pageid="190" ns="6" title="File:Basement water mold.gif" />
      <page pageid="204" ns="6" title="File:Basement with waterheater.gif" />
    </pages>
  </query>
</api>