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chromium/third_party/blink/web_tests/external/wpt/html/editing/dnd/dropzone/001.xhtml 

<?xml version="1.0" encoding="utf-8"?>
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title>Dropzone attribute: copy</title>
<style type="text/css">
div
  {background-color:navy;
  width:40px;
  height:40px;
  padding:40px;
  color:white;}
</style>
</head>
<body onload="window.getSelection().selectAllChildren(document.querySelector('p'))">
<p>Drag me</p>
<div dropzone="copy string:text/plain" ondrop="document.querySelector('div').appendChild(document.createTextNode((event.dataTransfer.getData('text/plain') == 'Drag me')?'PASS':'FAIL'))"/>
<p>You should be able to drag selection to navy box below. You should see word PASS once you drop it.</p>
</body>
</html>