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>
    <namespaces>
      <ns id="-2" case="first-letter" canonical="Media" xml:space="preserve">Медиа</ns>
      <ns id="-1" case="first-letter" canonical="Special" xml:space="preserve">Служебная</ns>
      <ns id="0" case="first-letter" content="" xml:space="preserve" />
      <ns id="1" case="first-letter" subpages="" canonical="Talk" xml:space="preserve">Обсуждение</ns>
      <ns id="2" case="first-letter" subpages="" canonical="User" xml:space="preserve">Участник</ns>
      <ns id="3" case="first-letter" subpages="" canonical="User talk" xml:space="preserve">Обсуждение участника</ns>
      <ns id="4" case="first-letter" subpages="" canonical="Project" xml:space="preserve">wiki.standart-n.ru</ns>
      <ns id="5" case="first-letter" subpages="" canonical="Project talk" xml:space="preserve">Обсуждение wiki.standart-n.ru</ns>
      <ns id="6" case="first-letter" canonical="File" xml:space="preserve">Файл</ns>
      <ns id="7" case="first-letter" subpages="" canonical="File talk" xml:space="preserve">Обсуждение файла</ns>
      <ns id="8" case="first-letter" subpages="" canonical="MediaWiki" xml:space="preserve">MediaWiki</ns>
      <ns id="9" case="first-letter" subpages="" canonical="MediaWiki talk" xml:space="preserve">Обсуждение MediaWiki</ns>
      <ns id="10" case="first-letter" canonical="Template" xml:space="preserve">Шаблон</ns>
      <ns id="11" case="first-letter" subpages="" canonical="Template talk" xml:space="preserve">Обсуждение шаблона</ns>
      <ns id="12" case="first-letter" subpages="" canonical="Help" xml:space="preserve">Справка</ns>
      <ns id="13" case="first-letter" subpages="" canonical="Help talk" xml:space="preserve">Обсуждение справки</ns>
      <ns id="14" case="first-letter" canonical="Category" xml:space="preserve">Категория</ns>
      <ns id="15" case="first-letter" subpages="" canonical="Category talk" xml:space="preserve">Обсуждение категории</ns>
      <ns id="100" case="first-letter" canonical="Help" nonincludable="" xml:space="preserve">Help</ns>
      <ns id="101" case="first-letter" canonical="Help talk" nonincludable="" xml:space="preserve">Help talk</ns>
      <ns id="102" case="first-letter" canonical="Problems" nonincludable="" xml:space="preserve">Problems</ns>
      <ns id="103" case="first-letter" canonical="Problems talk" nonincludable="" xml:space="preserve">Problems talk</ns>
      <ns id="104" case="first-letter" canonical="Clients" nonincludable="" xml:space="preserve">Clients</ns>
      <ns id="105" case="first-letter" canonical="Clients talk" nonincludable="" xml:space="preserve">Clients talk</ns>
      <ns id="106" case="first-letter" canonical="Reglament" nonincludable="" xml:space="preserve">Reglament</ns>
      <ns id="107" case="first-letter" canonical="Reglament talk" nonincludable="" xml:space="preserve">Reglament talk</ns>
      <ns id="108" case="first-letter" canonical="Duty" nonincludable="" xml:space="preserve">Duty</ns>
      <ns id="109" case="first-letter" canonical="Duty talk" nonincludable="" xml:space="preserve">Duty talk</ns>
      <ns id="110" case="first-letter" canonical="Contacts" nonincludable="" xml:space="preserve">Contacts</ns>
      <ns id="111" case="first-letter" canonical="Contacts talk" nonincludable="" xml:space="preserve">Contacts talk</ns>
      <ns id="112" case="first-letter" canonical="Versions" nonincludable="" xml:space="preserve">Versions</ns>
      <ns id="113" case="first-letter" canonical="Versions talk" nonincludable="" xml:space="preserve">Versions talk</ns>
      <ns id="114" case="first-letter" canonical="Econv" nonincludable="" xml:space="preserve">Econv</ns>
      <ns id="115" case="first-letter" canonical="Econv talk" nonincludable="" xml:space="preserve">Econv talk</ns>
      <ns id="116" case="first-letter" canonical="Vnedrenie" nonincludable="" xml:space="preserve">Vnedrenie</ns>
      <ns id="117" case="first-letter" canonical="Vnedrenie talk" nonincludable="" xml:space="preserve">Vnedrenie talk</ns>
      <ns id="118" case="first-letter" canonical="Managers" nonincludable="" xml:space="preserve">Managers</ns>
      <ns id="119" case="first-letter" canonical="Managers talk" nonincludable="" xml:space="preserve">Managers talk</ns>
      <ns id="120" case="first-letter" canonical="SysAdmin" nonincludable="" xml:space="preserve">SysAdmin</ns>
      <ns id="121" case="first-letter" canonical="SysAdmin talk" nonincludable="" xml:space="preserve">SysAdmin talk</ns>
      <ns id="122" case="first-letter" canonical="Developers" nonincludable="" xml:space="preserve">Developers</ns>
      <ns id="123" case="first-letter" canonical="Developers talk" nonincludable="" xml:space="preserve">Developers talk</ns>
    </namespaces>
  </query>
</api>