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="1" ns="0" title="Main Page">
        <images>
          <im ns="6" title="File:DM200908 2119 111w.jpg" />
          <im ns="6" title="File:DM201607 067 11w.jpg" />
          <im ns="6" title="File:NHM 350 1 11.jpg" />
          <im ns="6" title="File:OmIllus NebNatBank 1888 w.jpg" />
          <im ns="6" title="File:RG2608-1053 SFN10604a 2w.jpg" />
        </images>
      </page>
    </pages>
  </query>
</api>