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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="RNAウイルス" />
</query-continue>
<query>
<allcategories>
<c size="0" pages="0" files="0" subcats="0" xml:space="preserve">4類感染症</c>
<c size="0" pages="0" files="0" subcats="0" xml:space="preserve">CT</c>
<c size="1" pages="0" files="1" subcats="0" xml:space="preserve">Documentation examples</c>
<c size="1" pages="1" files="0" subcats="0" xml:space="preserve">Exclude in print</c>
<c size="2" pages="2" files="0" subcats="0" xml:space="preserve">Help/ja</c>
<c size="1" pages="1" files="0" subcats="0" xml:space="preserve">Info templates/ja</c>
<c size="4" pages="4" files="0" subcats="0" xml:space="preserve">Languages pages</c>
<c size="4" pages="4" files="0" subcats="0" xml:space="preserve">Languages pages without translations</c>
<c size="0" pages="0" files="0" subcats="0" xml:space="preserve">MRI</c>
<c size="1" pages="1" files="0" subcats="0" xml:space="preserve">NSAIDs</c>
</allcategories>
</query>
</api>