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>
    <alllinks galcontinue="Bookstore|1979" />
  </query-continue>
  <query>
    <pages>
      <page pageid="397" ns="8" title="MediaWiki:Menu/en" />
      <page pageid="553" ns="0" title="Дяченки Марина та Сергій" />
      <page pageid="774" ns="0" title="Джанікян Арсен" />
      <page pageid="2519" ns="0" title="А-ба-ба-га-ла-мазька книжкова колекція поповнилася англомовними новинками" />
      <page pageid="2727" ns="0" title="Arsen Dzhanikyan" />
      <page pageid="2930" ns="0" title="Birds from an invisible island" />
      <page pageid="2931" ns="0" title="Birds From an Invisible Island" />
      <page pageid="2997" ns="0" title="Valeriy Shevchuk" />
      <page pageid="3083" ns="0" title="Maryna &amp; Serhiy Dyachenko" />
      <page pageid="3723" ns="14" title="Category:Back issues" />
    </pages>
  </query>
</api>