<html>
<head>
<script>
function onLoad() {
  // For emulating the traditional behavior, collapse Selection to end of the
  // last text node of the <body> (end of the text node after the <p hidden>).
  getSelection().collapse(
    document.body.lastChild,
    document.body.lastChild.length
  );
  getSelection().setPosition(
    document.querySelector("hr"),
    0
  );
  document.execCommand("delete");
}
</script>
<body onload="onLoad()">
<p hidden>
    <canvas contenteditable>
        <hr contenteditable>
        3uW4*</hr></canvas>
</p>
</body>
</html>