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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="Geografie_České_republiky" />
  </query-continue>
  <query>
    <allcategories>
      <c size="1" pages="1" files="0" subcats="0" xml:space="preserve">Brněnec</c>
      <c size="0" pages="0" files="0" subcats="0" xml:space="preserve">Bývalé městyse v Česku</c>
      <c size="1" pages="1" files="0" subcats="0" xml:space="preserve">Bývalé městyse v České republice</c>
      <c size="1" pages="1" files="0" subcats="0" xml:space="preserve">Bývalé obce na pomezí Čech a Moravy</c>
      <c size="1" pages="1" files="0" subcats="0" xml:space="preserve">Bělá nad Svitavou</c>
      <c size="2" pages="2" files="0" subcats="0" xml:space="preserve">Březová nad Svitavou</c>
      <c size="2" pages="2" files="0" subcats="0" xml:space="preserve">Dokumentace šablon</c>
      <c size="2" pages="2" files="0" subcats="0" xml:space="preserve">Fakta k ověření</c>
      <c size="2" pages="2" files="0" subcats="0" xml:space="preserve">Fixme:LocMap</c>
      <c size="1" pages="1" files="0" subcats="0" xml:space="preserve">Geografické navigační šablony</c>
    </allcategories>
  </query>
</api>