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="1038" ns="12" title="Help:Incorporating Images and Other Files into Cases" url="http://www.mediawiki.org/wiki/Extension:EmbedVideo" />
      <eu pageid="838" ns="10" title="Template:DiscussionInstructions" url="http://www.mediawiki.org/wiki/Help:Extension:LiquidThreads" />
      <eu pageid="839" ns="3" title="User talk:Amanda" url="http://www.mediawiki.org/wiki/Help:Extension:LiquidThreads" />
      <eu pageid="654" ns="3" title="User talk:ACR" url="http://www.mediawiki.org/wiki/Help:Extension:LiquidThreads" />
      <eu pageid="840" ns="3" title="User talk:Mpritchard" url="http://www.mediawiki.org/wiki/Help:Extension:LiquidThreads" />
      <eu pageid="841" ns="3" title="User talk:Lawrence Susskind" url="http://www.mediawiki.org/wiki/Help:Extension:LiquidThreads" />
      <eu pageid="842" ns="3" title="User talk:Shafiqul Islam" url="http://www.mediawiki.org/wiki/Help:Extension:LiquidThreads" />
      <eu pageid="843" ns="3" title="User talk:Mark Rafferty" url="http://www.mediawiki.org/wiki/Help:Extension:LiquidThreads" />
      <eu pageid="844" ns="3" title="User talk:Rose Wang" url="http://www.mediawiki.org/wiki/Help:Extension:LiquidThreads" />
      <eu pageid="563" ns="10" title="Template:DiscussionHeader" url="http://www.mediawiki.org/wiki/Help:Extension:LiquidThreads" />
    </exturlusage>
  </query>
</api>