chromium/third_party/blink/web_tests/external/wpt/selection/shadow-dom/cross-shadow-boundary-6-ref.html

<!doctype html>
<span id="span">Start
<div>
  <span id="inner1">inner1</p>
  <span id="inner2">inner2</p>
</div>
</span>
<script>
  const start = document.getElementById("span").firstChild;
  const end = document.getElementById("inner2");
  window.getSelection().setBaseAndExtent(start, 3, end.firstChild, 3);
</script>