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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.
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<?xml version="1.0"?>
<api>
  <query-continue>
    <allcategories accontinue="Индикаторы_волатильности" />
  </query-continue>
  <query>
    <allcategories>
      <c size="15" pages="15" files="0" subcats="0" xml:space="preserve">Бинарные опционы</c>
      <c size="30" pages="30" files="0" subcats="0" xml:space="preserve">Брокеры Форекс</c>
      <c size="27" pages="27" files="0" subcats="0" xml:space="preserve">Валютные пары</c>
      <c size="0" pages="0" files="0" subcats="0" xml:space="preserve">Википедия:индикоторы</c>
      <c size="10" pages="10" files="0" subcats="0" xml:space="preserve">Волны Элиота</c>
      <c size="4" pages="4" files="0" subcats="0" xml:space="preserve">Время на рынке Форекс</c>
      <c size="4" pages="4" files="0" subcats="0" xml:space="preserve">Графики</c>
      <c size="17" pages="17" files="0" subcats="0" xml:space="preserve">Графические фигуры</c>
      <c size="1" pages="1" files="0" subcats="0" xml:space="preserve">Индексы</c>
      <c size="104" pages="104" files="0" subcats="0" xml:space="preserve">Индикаторы</c>
    </allcategories>
  </query>
</api>