code: public Element nextElementSibling() {
          if (parentNode == null) return null;
          List<Element> siblings = parent().childElementsList();
          Integer index = indexInList(this, siblings);
          Validate.notNull(index);
          if (siblings.size() > index+1)
              return siblings.get(index+1);
          else
              return null;
      }
docs: Gets the next sibling element of this element. E.g., if a {@code div} contains two {@code p}s,
  the {@code nextElementSibling} of the first {@code p} is the second {@code p}.
  <p>
  This is similar to {@link #nextSibling()}, but specifically finds only Elements
  </p>
  @return the next element, or null if there is no next element
  @see #previousElementSibling()