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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 pageid="2518" ns="0" title="Main Page">
        <templates>
          <tl ns="10" title="Template:CenterGreyBox" />
          <tl ns="10" title="Template:GreyTitle" />
        </templates>
      </page>
    </pages>
  </query>
</api>