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="100058358" ns="2" title="User:J. Noel Chiappa/Links" url="http://www.mediawiki.org/wiki?title=Extension:TreeAndMenu" />
      <eu pageid="100058358" ns="2" title="User:J. Noel Chiappa/Links" url="http://www.mediawiki.org/wiki?title=Extension:DynamicPageList" />
      <eu pageid="100009554" ns="10" title="Template:Click" url="http://www.mediawiki.org/wiki/Extension:ImageMap" />
      <eu pageid="100022596" ns="3" title="User talk:Larry Sanger/Archive 6" url="http://www.mediawiki.org/wiki/Extension:FlaggedRevs" />
      <eu pageid="100055977" ns="2" title="User:J. Noel Chiappa" url="http://www.mediawiki.org/wiki?title=Extension:TreeAndMenu" />
      <eu pageid="100055977" ns="2" title="User:J. Noel Chiappa" url="http://www.mediawiki.org/wiki?title=Extension:DynamicPageList" />
      <eu pageid="100022596" ns="3" title="User talk:Larry Sanger/Archive 6" url="http://www.mediawiki.org/wiki/Manual:$wgAllowDisplayTitle" />
      <eu pageid="100067499" ns="2" title="User:Daniel Mietchen/Notes to self" url="http://www.mediawiki.org/wiki/Manual:MediaWiki_feature_list" />
      <eu pageid="100067499" ns="2" title="User:Daniel Mietchen/Notes to self" url="http://www.mediawiki.org/wiki/Extension:FCKeditor_(Official)" />
      <eu pageid="100021006" ns="11" title="Template talk:Subpages" url="http://www.mediawiki.org/wiki/Extension:StringFunctions" />
    </exturlusage>
  </query>
</api>