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="被保护的模板" />
  </query-continue>
  <query>
    <allcategories>
      <c size="3" pages="3" files="0" subcats="0" xml:space="preserve">保护状态与保护标志不符的页面</c>
      <c size="7" pages="7" files="0" subcats="0" xml:space="preserve">卫生统计学</c>
      <c size="0" pages="0" files="0" subcats="0" xml:space="preserve">有受损文件链接的页面</c>
      <c size="1" pages="1" files="0" subcats="0" xml:space="preserve">有机氯化合物</c>
      <c size="1" pages="1" files="0" subcats="0" xml:space="preserve">杀虫剂</c>
      <c size="2" pages="2" files="0" subcats="0" xml:space="preserve">生物化学</c>
      <c size="3" pages="0" files="0" subcats="3" xml:space="preserve">病原微生物学</c>
      <c size="0" pages="0" files="0" subcats="0" xml:space="preserve">真菌学</c>
      <c size="1" pages="1" files="0" subcats="0" xml:space="preserve">细菌学</c>
      <c size="2" pages="2" files="0" subcats="0" xml:space="preserve">营养与食品卫生学</c>
    </allcategories>
  </query>
</api>