You are looking at the HTML representation of the XML format.
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="Analog" />
  </query-continue>
  <query>
    <allcategories>
      <c size="1" pages="1" files="0" subcats="0" xml:space="preserve">ARM Linux Mini PC</c>
      <c size="1" pages="1" files="0" subcats="0" xml:space="preserve">ASI Capture Card</c>
      <c size="15" pages="9" files="0" subcats="6" xml:space="preserve">ATSC</c>
      <c size="1" pages="1" files="0" subcats="0" xml:space="preserve">ATSC ExpressCard Devices</c>
      <c size="1" pages="1" files="0" subcats="0" xml:space="preserve">ATSC HD TV Tuner</c>
      <c size="1" pages="1" files="0" subcats="0" xml:space="preserve">ATSC IEEE1394 Devices</c>
      <c size="1" pages="1" files="0" subcats="0" xml:space="preserve">ATSC Network Attached Devices</c>
      <c size="33" pages="33" files="0" subcats="0" xml:space="preserve">ATSC PCI Cards</c>
      <c size="13" pages="13" files="0" subcats="0" xml:space="preserve">ATSC PCIe Cards</c>
      <c size="30" pages="30" files="0" subcats="0" xml:space="preserve">ATSC USB Devices</c>
    </allcategories>
  </query>
</api>