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="18777_1w.jpg" />
  </query-continue>
  <query>
    <pages>
      <page pageid="5457" ns="6" title="File:008 3w.jpg" />
      <page pageid="5456" ns="6" title="File:027 1w.jpg" />
      <page pageid="2373" ns="6" title="File:02 Monza Cappella espiatoria 1w.jpg" />
      <page pageid="4724" ns="6" title="File:067 1w.jpg" />
      <page pageid="5647" ns="6" title="File:0F51CB55-.jpg" />
      <page pageid="987" ns="6" title="File:108616 1w.jpg" />
      <page pageid="5472" ns="6" title="File:1280px-Opa Locka FL city hall01 1w.jpg" />
      <page pageid="4725" ns="6" title="File:130 1w.jpg" />
      <page pageid="986" ns="6" title="File:17630 1w.jpg" />
      <page pageid="5754" ns="6" title="File:1871 OSATMullettpp8 9.jpg" />
    </pages>
  </query>
</api>