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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="9" name="Yokimato" />
      <u userid="53" name="Yonta" />
      <u userid="44" name="Yotam" />
      <u userid="64" name="Zabeva" />
      <u userid="76" name="ZenonFrank6" />
      <u userid="26" name="Zigmundovich" />
    </allusers>
  </query>
</api>