chromium/third_party/blink/web_tests/external/wpt/selection/shadow-dom/cross-shadow-boundary-4.html

<!doctype html>
<head>
<!--Intentionally to use cross-shadow-boundary-3-ref.html here-->
<link rel=match href="cross-shadow-boundary-3-ref.html">
</head>
OuterText
<div id="host1"></div>
OuterText
<div id="host2"></div>
<script>
  const root1 = document.getElementById("host1").attachShadow({ mode: "open" });
  root1.innerHTML = "innerText1";

  const root2 = document.getElementById("host2").attachShadow({ mode: "open" });
  root2.innerHTML = "<div></div>";

  const root3 = root2.querySelector("div").attachShadow({ mode: "open" });
  root3.innerHTML = "innerText2";

  getSelection().setBaseAndExtent(root1.firstChild, 3, root3.firstChild, 3);
</script>