chromium/content/test/data/accessibility/event/aria-textbox-with-focusable-children.html

<!DOCTYPE html>
<html>
<body>
<div role="textbox" tabindex="0">
  focusable:
  <button id="btn1">not editable</button>
</div>
<div role="textbox" contenteditable>
  focusable:
  <button id="btn2">editable</button>
</div>
<script>
  var go_passes = [
    () => document.getElementById("btn1").focus(),
    () => document.getElementById("btn2").focus(),
  ];

  var current_pass = 0;
  function go() {
    go_passes[current_pass++].call();
    return current_pass < go_passes.length;
  }
</script>
</body>
</html>