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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="2004_albums" />
</query-continue>
<query>
<allcategories>
<c size="1" pages="1" files="0" subcats="0" xml:space="preserve">00s Albums</c>
<c size="194" pages="194" files="0" subcats="0" xml:space="preserve">00s Bands</c>
<c size="13" pages="13" files="0" subcats="0" xml:space="preserve">10s Bands</c>
<c size="1" pages="1" files="0" subcats="0" xml:space="preserve">1975 albums</c>
<c size="1" pages="1" files="0" subcats="0" xml:space="preserve">1977 singles</c>
<c size="2" pages="2" files="0" subcats="0" xml:space="preserve">1981 singles</c>
<c size="1" pages="1" files="0" subcats="0" xml:space="preserve">1997 albums</c>
<c size="1" pages="1" files="0" subcats="0" xml:space="preserve">1999 albums</c>
<c size="1" pages="1" files="0" subcats="0" xml:space="preserve">2001 albums</c>
<c size="1" pages="1" files="0" subcats="0" xml:space="preserve">2003 albums</c>
</allcategories>
</query>
</api>