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>
    <pages>
      <page pageid="5" ns="0" title="Vector" />
      <page pageid="6" ns="0" title="Vector(Вектор-М)" />
      <page pageid="65" ns="0" title="Настройка параметров ядра и системы" />
      <page pageid="66" ns="0" title="Установка БД Oracle 11g" />
      <page pageid="67" ns="0" title="Установка СУБ Oracle 11g" />
      <page pageid="68" ns="0" title="Вектор-М(Vector)" />
      <page pageid="101" ns="0" title="Chmod" />
      <page pageid="157" ns="0" title="Установка ZooKeeper на ОС CentOS 7.3" />
      <page pageid="187" ns="0" title="Настройка ОС для серверов буферных хранилищ Oracle" />
    </pages>
  </query>
</api>