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>
    <alltransclusions gatcontinue="Cc-by-nc-nd-2.5|2883" />
  </query-continue>
  <query>
    <pages>
      <page pageid="2577" ns="6" title="File:Strehlow garage w.jpg" />
      <page pageid="2582" ns="6" title="File:NHM 211 02 02 Crook House.jpg" />
      <page pageid="2780" ns="6" title="File:Federal bldg 001 w.jpg" />
      <page pageid="2799" ns="6" title="File:JC146 w.jpg" />
      <page pageid="2873" ns="6" title="File:ThomasLeeKaspar ca2017 1w.jpg" />
      <page pageid="2875" ns="6" title="File:First West Side Bank 11w.jpg" />
      <page pageid="2876" ns="6" title="File:Ford Residence Front 1w.jpg" />
      <page pageid="2877" ns="6" title="File:Indian Hills Inn 1w.jpg" />
      <page pageid="2878" ns="6" title="File:LUEDER BUILDING 11w.jpg" />
      <page pageid="2879" ns="6" title="File:PinkertonAndCompany 1w.jpg" />
    </pages>
  </query>
</api>