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>
    <exturlusage euoffset="10" />
  </query-continue>
  <query>
    <exturlusage>
      <eu pageid="8" ns="12" title="Help:Wiki Help Resources" url="http://www.mediawiki.org/w/index.php?title=Help:Cleanup&amp;action=edit" />
      <eu pageid="8" ns="12" title="Help:Wiki Help Resources" url="http://www.mediawiki.org/w/index.php?title=Help:Managing_pages&amp;action=edit" />
      <eu pageid="1688" ns="0" title="MediaWiki Upgrade April 2011" url="http://www.mediawiki.org/wiki/Download" />
      <eu pageid="2196" ns="0" title="MediaWiki Upgrade January 2014" url="http://www.mediawiki.org/wiki/Extension_talk:MobileFrontend#HTTPs_in_Mobile_View_Link_36904" />
      <eu pageid="8" ns="12" title="Help:Wiki Help Resources" url="http://www.mediawiki.org/wiki/Help:Categories" />
      <eu pageid="8" ns="12" title="Help:Wiki Help Resources" url="http://www.mediawiki.org/wiki/Help:Copying" />
      <eu pageid="8" ns="12" title="Help:Wiki Help Resources" url="http://www.mediawiki.org/wiki/Help:Editing_pages" />
      <eu pageid="8" ns="12" title="Help:Wiki Help Resources" url="http://www.mediawiki.org/wiki/Help:Formatting" />
      <eu pageid="8" ns="12" title="Help:Wiki Help Resources" url="http://www.mediawiki.org/wiki/Help:Images" />
      <eu pageid="8" ns="12" title="Help:Wiki Help Resources" url="http://www.mediawiki.org/wiki/Help:Interwiki_linking" />
    </exturlusage>
  </query>
</api>