*       can't change, and it is faster because many writers and appendables are optimized for
   *       appending string instances.
   * </ul>
   */
  private static class StringCharSource extends CharSequenceCharSource {
    StringCharSource(String seq) {
      super(seq);
    }

    @Override
    public Reader openStream() {
      return new StringReader((String) seq);
    }

    @Override