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="10" ns="100" title="Private:Protein Service LIMS" url="http://www.mediawiki.org" />
      <eu pageid="10" ns="100" title="Private:Protein Service LIMS" url="http://www.mediawiki.org/wiki/Extension:ConfirmAccount" />
      <eu pageid="799" ns="100" title="Private:Proteomics LIMS/User" url="http://www.mediawiki.org/wiki/Extension:ConfirmAccount" />
      <eu pageid="10" ns="100" title="Private:Protein Service LIMS" url="http://www.mediawiki.org/wiki/Extension:ConfirmEdit" />
      <eu pageid="819" ns="100" title="Private:Process Wiki" url="http://www.mediawiki.org/wiki/Extension:FileLink" />
      <eu pageid="1029" ns="100" title="Private:Lab Service Wiki/SMWCon 2011" url="http://www.mediawiki.org/wiki/Extension:ImageRefer" />
      <eu pageid="819" ns="100" title="Private:Process Wiki" url="http://www.mediawiki.org/wiki/Extension:Page_Object_Model" />
      <eu pageid="10" ns="100" title="Private:Protein Service LIMS" url="http://www.mediawiki.org/wiki/Extension:Semantic_Forms#Preloading_data" />
      <eu pageid="883" ns="100" title="Private:PRGdb" url="http://www.mediawiki.org/wiki/Extension:Semantic_Result_Formats/bibtex_format" />
      <eu pageid="10" ns="100" title="Private:Protein Service LIMS" url="http://www.mediawiki.org/wiki/Extension:Semantic_Tasks" />
    </exturlusage>
  </query>
</api>