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HTML is good for debugging, but is unsuitable for application use.
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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="Narrowboating" />
</query-continue>
<query>
<allcategories>
<c size="4" pages="4" files="0" subcats="0" xml:space="preserve">Debian</c>
<c size="1" pages="1" files="0" subcats="0" xml:space="preserve">Documentation see also templates</c>
<c size="2" pages="2" files="0" subcats="0" xml:space="preserve">Fedora</c>
<c size="7" pages="7" files="0" subcats="0" xml:space="preserve">Hosting</c>
<c size="2" pages="2" files="0" subcats="0" xml:space="preserve">Hosts</c>
<c size="1" pages="1" files="0" subcats="0" xml:space="preserve">Ideas</c>
<c size="7" pages="7" files="0" subcats="0" xml:space="preserve">Image with comment templates</c>
<c size="1" pages="1" files="0" subcats="0" xml:space="preserve">Kennet and Avon Canal</c>
<c size="3" pages="3" files="0" subcats="0" xml:space="preserve">Linux</c>
<c size="1" pages="1" files="0" subcats="0" xml:space="preserve">Meet and greet</c>
</allcategories>
</query>
</api>