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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.
See the complete documentation, or API help for more information.
<?xml version="1.0"?>
<api>
  <query-continue>
    <allcategories accontinue="Language_link_templates" />
  </query-continue>
  <query>
    <allcategories>
      <c size="3" pages="3" files="0" subcats="0" xml:space="preserve">Autotranslated templates</c>
      <c size="1" pages="1" files="0" subcats="0" xml:space="preserve">CC-BY</c>
      <c size="1" pages="1" files="0" subcats="0" xml:space="preserve">Design and review tools</c>
      <c size="3" pages="3" files="0" subcats="0" xml:space="preserve">Exclude in print</c>
      <c size="2" pages="2" files="0" subcats="0" xml:space="preserve">Formatting templates</c>
      <c size="1" pages="1" files="0" subcats="0" xml:space="preserve">Function templates</c>
      <c size="0" pages="0" files="0" subcats="0" xml:space="preserve">Images without source</c>
      <c size="1" pages="1" files="0" subcats="0" xml:space="preserve">Infobox templates</c>
      <c size="1" pages="1" files="0" subcats="0" xml:space="preserve">Internal link templates</c>
      <c size="2" pages="2" files="0" subcats="0" xml:space="preserve">Internationalization templates</c>
    </allcategories>
  </query>
</api>