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HTML is good for debugging, but probably is not suitable for your application.
See complete documentation, or API help for more information. 
<?xml version="1.0"?>
<api>
  <query>
    <allusers>
      <u userid="72" name="Youth culture" />
      <u userid="95" name="Zakkwidzyn" />
      <u userid="331" name="Zanetakalmar" />
      <u userid="312" name="Zbyszek1987" />
    </allusers>
  </query>
</api>