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<html>
 <head>
  <title>Longdesc test: empty longdesc</title>
 </head>
 <body>
<h1>Longdesc test: empty longdesc value</h1>
<p><img src="picture.png" alt="the image" longdesc=""></p>
<p>The longdesc attribute value is null, and therefore the longdesc is not valid.</p>
 </body>
</html>