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="11" ns="0" title="Mediawiki" url="http://www.mediawiki.org" />
      <eu pageid="915" ns="100" title="Blog:Hacks/A simple way to quote from bibTeX in MediaWiki" url="http://www.mediawiki.org/wiki/Category:Referencing_extensions" />
      <eu pageid="929" ns="100" title="Blog:Hacks/Positioning the frame of extension Anysite" url="http://www.mediawiki.org/wiki/Extension:Anysite" />
      <eu pageid="915" ns="100" title="Blog:Hacks/A simple way to quote from bibTeX in MediaWiki" url="http://www.mediawiki.org/wiki/Extension:Cite" />
      <eu pageid="17" ns="0" title="LaussyWiki" url="http://www.mediawiki.org/wiki/Extension:Cite/Cite.php" />
      <eu pageid="67" ns="0" title="Code" url="http://www.mediawiki.org/wiki/Extension:Code" />
      <eu pageid="779" ns="100" title="Blog:Hacks/Commenting on blog posts" url="http://www.mediawiki.org/wiki/Extension:Comments" />
      <eu pageid="17" ns="0" title="LaussyWiki" url="http://www.mediawiki.org/wiki/Extension:FancyBoxThumbs" />
      <eu pageid="301" ns="0" title="MediaWiki&#039;s Google maps" url="http://www.mediawiki.org/wiki/Extension:Google_Maps" />
      <eu pageid="7845" ns="100" title="Blog:Hacks/From maps to multimaps" url="http://www.mediawiki.org/wiki/Extension:Google_Maps" />
    </exturlusage>
  </query>
</api>