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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>
    <pages>
      <page ns="14" title="Category:List templates" missing="" />
      <page ns="14" title="Category:Lists of festivals by topic" missing="" />
      <page ns="14" title="Category:Lists of observances" missing="" />
    </pages>
  </query>
</api>