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="8571" ns="0" title="Chess" url="http://www.mediawiki.org/wiki/Extension:EmbedChessboard" />
      <eu pageid="8200" ns="0" title="How to upload a video" url="http://www.mediawiki.org/wiki/Extension:Player#Tag_Attributes" />
      <eu pageid="19" ns="0" title="News" url="http://www.mediawiki.org/wiki/Extension:SyntaxHighlight_GeSHi" />
      <eu pageid="13" ns="0" title="Rhea Team" url="http://www.mediawiki.org/wiki/Extension:SyntaxHighlight_GeSHi" />
      <eu pageid="11" ns="0" title="Rhea Course Template 1" url="http://www.mediawiki.org/wiki/Help:Categories" />
      <eu pageid="289" ns="0" title="ECE201 (Spring2009)" url="http://www.mediawiki.org/wiki/Help:Categories" />
      <eu pageid="291" ns="0" title="Main Page ECE302Fall2008sanghavi" url="http://www.mediawiki.org/wiki/Manual:Configuration_settings" />
      <eu pageid="703" ns="0" title="Main Page ECE462Fall2008yunglu" url="http://www.mediawiki.org/wiki/Manual:Configuration_settings" />
      <eu pageid="845" ns="0" title="Main Page ECE538Fall2008mikedz" url="http://www.mediawiki.org/wiki/Manual:Configuration_settings" />
      <eu pageid="847" ns="0" title="Main Page ECE602Fall2008decarlo" url="http://www.mediawiki.org/wiki/Manual:Configuration_settings" />
    </exturlusage>
  </query>
</api>