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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="Calcolo_termini_processuali" />
  </query-continue>
  <query>
    <allcategories>
      <c size="1" pages="1" files="0" subcats="0" xml:space="preserve">(DL 18-2020)</c>
      <c size="5" pages="5" files="0" subcats="0" xml:space="preserve">Aiuto</c>
      <c size="2" pages="2" files="0" subcats="0" xml:space="preserve">Altri modelli</c>
      <c size="0" pages="0" files="0" subcats="0" xml:space="preserve">Altro</c>
      <c size="0" pages="0" files="0" subcats="0" xml:space="preserve">Attestazioni di conformità</c>
      <c size="0" pages="0" files="0" subcats="0" xml:space="preserve">C.c. (Codice Civile</c>
      <c size="3229" pages="3228" files="0" subcats="1" xml:space="preserve">C.c. (Codice Civile)</c>
      <c size="870" pages="870" files="0" subcats="0" xml:space="preserve">C.p. (Codice Penale)</c>
      <c size="1057" pages="1057" files="0" subcats="0" xml:space="preserve">C.p.c. (Codice di Procedura Civile)</c>
      <c size="873" pages="873" files="0" subcats="0" xml:space="preserve">C.p.p. (Codice di Procedura Penale)</c>
    </allcategories>
  </query>
</api>