public static final String BEFORE_FIRST_2 = "\0\0";
    public static final String MIN_ELEMENT = "a";
    public static final String AFTER_LAST = "z";
    public static final String AFTER_LAST_2 = "zz";
  }

  public static class Chars extends SampleElements<Character> {
    public Chars() {
      // elements aren't sorted, to better test SortedSet iteration ordering
      super('b', 'a', 'c', 'd', 'e');
    }