<?xml version="1.0" encoding="utf-8"?>
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title>Dropping image on vertical iframe scrollbar</title>
<style type="text/css">
p:first-child
  {padding-left:1em;}
iframe
  {height:6em;
  width:3em;}
img
  {width:5px;
  height:5px;}
</style>
<script type="application/ecmascript">
function dragImage()
  {event.dataTransfer.effectAllowed = 'copy';}
function dropImage(event)
  {document.querySelector('p + p').firstChild.nodeValue = 'PASS';}
</script>
</head>
<body ondragenter="event.preventDefault()" ondragover="return false">
<p><img src="data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAIAAAACCAYAAABytg0kAAAAEElEQVR42mNgaGD4D8YwBgAw9AX9Y9zBwwAAAABJRU5ErkJggg==" alt="PNG green pixel" ondragstart="dragImage()" ondragend="dropImage(event)"/></p>
<p>Drag little square above and drop it on vertical scrollbar. Word PASS should appear once you drop it.</p>
<iframe src="helper-drop-vertical-scrollbar.xhtml">XHTML document</iframe>
</body>
</html>