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>
    <allfileusages gafcontinue="Billing-account-register-01.png|1032" />
  </query-continue>
  <query>
    <pages>
      <page pageid="629" ns="0" title="Billing - Account" />
      <page pageid="691" ns="0" title="Client Area - Two Factor Authentication" />
      <page pageid="922" ns="0" title="Billing - Register Account" />
      <page pageid="992" ns="0" title="How to Check Affiliate Balance" />
      <page pageid="996" ns="0" title="Obtain Affiliate Links &amp; Banners" />
      <page pageid="1004" ns="0" title="Ordering SSL Certificate" />
      <page pageid="1009" ns="0" title="Cancel Domain Registration" />
      <page pageid="1024" ns="0" title="Domain Forwarding(Domain Management)" />
    </pages>
  </query>
</api>