llection = rootCollection.children[3].children[0];
  const keysInSubCollection = subCollection.querySelectorAll(":scope > key");
  const clonedSubCollection = subCollection.cloneNode(true);
  const keysInClonedSubCollection =
    clonedSubCollection.querySelectorAll(":scope > key");
  assert_equals(subCollection.outerHTML, clonedSubCollection.outerHTML, "outerHTML");
  assert_equals(keysInSubCollection.length, keysInClonedSubCollection.length, "length");
  assert_equals(keysInSubCollection.item(0), xmlDocum