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chromium/third_party/blink/web_tests/external/wpt/html/editing/dnd/cross-document/002-manual.html 

<!DOCTYPE html>
<title>drag &amp; drop - cross-domain cross-document data drop</title>
<script src="../resources/crossorigin.sub.js"></script>
<style>
  body > div {
    height: 200px;
    width: 200px;
    background-color: orange;
  }
</style>

<script>
window.onload = function() {
  var orange = document.getElementsByTagName('div')[0];
  orange.ondragstart = function(e) {
    e.dataTransfer.effectAllowed = 'copy';
    e.dataTransfer.setData('text', 'dummy text');
  };
};
</script>

<div draggable="true"></div>
<p><iframe height="300" width="500"></iframe></p>
<script>document.getElementsByTagName("iframe")[0].src = crossOriginUrl("www", "001-1.html");</script>
<noscript><p>Enable JavaScript and reload</p></noscript>