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="Автоматическая_очистка_устаревшей_информации" />
  </query-continue>
  <query>
    <pages>
      <page pageid="2013" ns="0" title="Sabre IBE B2B">
        <revisions>
          <rev />
        </revisions>
      </page>
      <page pageid="857" ns="0" title="Авиабилеты">
        <revisions>
          <rev />
        </revisions>
      </page>
    </pages>
  </query>
  <warnings>
    <revisions xml:space="preserve">Unrecognized value for parameter 'rvprop': content&quot;</revisions>
  </warnings>
</api>