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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="Executives" />
</query-continue>
<query>
<allcategories>
<c size="146" pages="146" files="0" subcats="0" xml:space="preserve">Alumni</c>
<c size="1" pages="1" files="0" subcats="0" xml:space="preserve">Articles pending deletion</c>
<c size="1" pages="1" files="0" subcats="0" xml:space="preserve">Articles that need Images</c>
<c size="1" pages="1" files="0" subcats="0" xml:space="preserve">Articles with things to do</c>
<c size="10" pages="10" files="0" subcats="0" xml:space="preserve">Articles with unsourced statements</c>
<c size="0" pages="0" files="0" subcats="0" xml:space="preserve">Category:Templates</c>
<c size="14" pages="14" files="0" subcats="0" xml:space="preserve">Chronicles</c>
<c size="2" pages="2" files="0" subcats="0" xml:space="preserve">Deceased Person</c>
<c size="1" pages="1" files="0" subcats="0" xml:space="preserve">Disambiguation pages</c>
<c size="2" pages="2" files="0" subcats="0" xml:space="preserve">Electronics</c>
</allcategories>
</query>
</api>