    <!--
                Copyright: Copyright 1998-2001 W3C (MIT, INRIA, Keio), All Rights Reserved.
    See http://www.w3.org/Consortium/Legal/.
    Author: Warner ten Kate (warner.ten.kate@philips.com), modified by Erik Hodge, RealNetworks
               Version: Mar 26, 2001, v2
                Module: SMIL Structure Module
               Feature: systemRequired on <smil> element
             File Name: Structure_systemRequired.smil
      Media Components: 3 JPG
     Expected Behavior: If the Obscure module is not supported, the document is not shown.
    -->
    <smil xmlns="http://www.w3.org/2001/SMIL20/Language"
          xmlns:Obscure="http://local.obscure.org/ofNoUse.dtd"
          systemRequired="Obscure" >
       <head>
          <layout>
             <region id="r1" top="0px" left="0px" height="240px" width="320px" />
          </layout>
       </head>
       <body>
          <seq>
             <img dur="5s" src="../images/frown.jpg"  region="r1"/>
             <img dur="5s" src="../images/smile.jpg" region="r1"/>
          </seq>
       </body>
    </smil>