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>
    <alllinks galcontinue="Cctbx.prime|123" />
  </query-continue>
  <query>
    <pages>
      <page pageid="1" ns="0" title="Main Page" />
      <page pageid="4" ns="0" title="Ha14 Tutorials" />
      <page pageid="15" ns="0" title="Metrology refinement" />
      <page pageid="21" ns="8" title="MediaWiki:Common.css" />
      <page pageid="75" ns="0" title="L498 Thermolysin" />
      <page pageid="90" ns="0" title="Gd-Lysozyme" />
      <page pageid="114" ns="0" title="Gd-Lysozyme-psana" />
      <page pageid="115" ns="0" title="Preparatory steps" />
    </pages>
  </query>
</api>