first partially contained child is not null:"
  } else if (firstPartiallyContainedChild) {
    // "Let clone be the result of calling cloneNode(false) on first
    // partially contained child."
    var clone = firstPartiallyContainedChild.cloneNode(false);

    // "Append clone as the last child of frag."
    frag.appendChild(clone);

    // "Let subrange be a new Range whose start is (original start node,
    // original start offset) and whose end is (first partially contained
    // child, length of fir