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>
    <allusers aufrom="同學11" />
  </query-continue>
  <query>
    <allusers>
      <u userid="1" name="丁志仁" />
      <u userid="20" name="丁禾" />
      <u userid="131" name="任懷鳴" />
      <u userid="74" name="何蕙如" />
      <u userid="17" name="劉國安" />
      <u userid="60" name="劉庭安" />
      <u userid="77" name="劉恩佑" />
      <u userid="63" name="同品樺" />
      <u userid="90" name="同學1" />
      <u userid="99" name="同學10" />
    </allusers>
  </query>
</api>