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="Yannick Patois 6284b1df6e" />
  </query-continue>
  <query>
    <allusers>
      <u userid="2456" name="Yaadav Bhauruth 592cf6c89c" />
      <u userid="773" name="Yacine Haddad 4be99d9e51" />
      <u userid="3838" name="Yamhis-eduroam@cern.ch 871a57ac72" />
      <u userid="1593" name="Yan Liu Rnf-601 94ad8a197f" />
      <u userid="3247" name="Yan Xiaofei 6cec976fec" />
      <u userid="735" name="Yan Xiaofei d058d1146b" />
      <u userid="737" name="Yan Xiaofei ea95681229" />
      <u userid="1092" name="Yana Douhaya 1f9ae5a32f" />
      <u userid="2082" name="Yannick Gladow 1d55afbbe1" />
      <u userid="2688" name="Yannick Patois 4a27987de0" />
    </allusers>
  </query>
</api>