chromium/third_party/blink/web_tests/external/wpt/selection/anonymous/details-ancestor.html

<!DOCTYPE html>
<meta charset="utf-8">
<title>Selecting internal node</title>
<script src=/resources/testharness.js></script>
<script src=/resources/testharnessreport.js></script>
<script src="/resources/testdriver.js"></script>
<script src="/resources/testdriver-vendor.js"></script>
<script src="/resources/testdriver-actions.js"></script>
<link rel="stylesheet" href="/fonts/ahem.css">
<style>
  details {
    font: 16px/1 Ahem;
  }
</style>
<details id="details"></details>
<script>
promise_test(async () => {
  await new test_driver.Actions()
    .pointerMove(5, 5, {origin: details})
    .pointerDown()
    .pointerMove(50, 50)
    .pointerUp()
    .send();
  const selection = getSelection();

  if (selection.anchorNode === null) {
    // <details> is not selectable, which is acceptable
    return;
  }

  // Gecko throws when accessing any property from DOM-invisible node
  // so check we can access something
  assert_equals(selection.anchorNode.constructor.name, "HTMLDetailsElement");
  assert_equals(selection.anchorOffset, 0);
  // Gecko limits the selection inside <details> while Blink does not
  // so check something general
  assert_equals(selection.focusNode.nodeType, Node.ELEMENT_NODE);
  assert_equals(selection.focusOffset, 0);
}, "Selecting the default summary of <details> should report a DOM-visible ancestor");
</script>