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>
    <allpages gapcontinue="Theile,_Wolfgang" />
  </query-continue>
  <query>
    <pages>
      <page pageid="915" ns="0" title="Tannenberg, Alfred Wolfgang von Wurzbach Ritter von" contentmodel="wikitext" pagelanguage="de" touched="2016-05-28T11:42:49Z" lastrevid="1143" counter="319" length="70" redirect="" new="" />
      <page pageid="830" ns="0" title="Tappolet, Ernst Emanuel" contentmodel="wikitext" pagelanguage="de" touched="2016-11-04T13:52:45Z" lastrevid="1723" counter="2890" length="2634" />
      <page pageid="831" ns="0" title="Ten Brink, Bernhard Aegidius Konrad (auch: Barend bzw. Bernard)" contentmodel="wikitext" pagelanguage="de" touched="2016-05-28T07:00:35Z" lastrevid="1605" counter="1306" length="2765" />
      <page pageid="832" ns="0" title="Terracini, Benvenuto Aronne" contentmodel="wikitext" pagelanguage="de" touched="2016-11-04T13:54:47Z" lastrevid="1724" counter="2421" length="2051" />
    </pages>
  </query>
</api>