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>
    <allcategories accontinue="郷土料理" />
  </query-continue>
  <query>
    <allcategories>
      <c size="1" pages="1" files="0" subcats="0" xml:space="preserve">アジアの食文化</c>
      <c size="1" pages="1" files="0" subcats="0" xml:space="preserve">サボテン科</c>
      <c size="1" pages="1" files="0" subcats="0" xml:space="preserve">メキシコの食文化</c>
      <c size="0" pages="0" files="0" subcats="0" xml:space="preserve">健康</c>
      <c size="1" pages="1" files="0" subcats="0" xml:space="preserve">健康食品</c>
      <c size="1" pages="1" files="0" subcats="0" xml:space="preserve">国際交流</c>
      <c size="0" pages="0" files="0" subcats="0" xml:space="preserve">壊れたファイルへのリンクがあるページ</c>
      <c size="1" pages="1" files="0" subcats="0" xml:space="preserve">旅行の形式</c>
      <c size="1" pages="1" files="0" subcats="0" xml:space="preserve">果物</c>
      <c size="1" pages="1" files="0" subcats="0" xml:space="preserve">栄養補助食品</c>
    </allcategories>
  </query>
</api>