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chromium/third_party/blink/web_tests/external/wpt/html/editing/dnd/file/prompt/005.html 

<!DOCTYPE html>
<title>drag &amp; drop - file drop prompt for special cases</title>
<style>
  body > div {
    height: 200px;
    width: 200px;
    background-color: orange;
  }
</style>

<script>
window.onload = function() {
  if( location.protocol == 'file:' || location.protocol == 'http:' || location.protocol == 'https:' ) {
    document.getElementsByTagName('p')[0].innerHTML = 'Use the source of this file as the source of special-case URLs within your browser, such as scriptable chrome: or opera: or attachment: URLs (eg. opera:config and send yourself the file as an email attachments and open the attachment in the browser).';
    return;
  }
  var orange = document.getElementsByTagName('div')[0];
  orange.ondragover = orange.ondragenter = orange.ondrop = function(e) {
    e.preventDefault();
  };
};
</script>

<div></div>

<p>Drag a file from your desktop onto the orange square. A prompt should appear, either showing the server name as unknown, or otherwise identifying this URL as the target of the upload.</p>
<noscript><p>Enable JavaScript and reload</p></noscript>