}
      }
    }
    // no replacement needed
    return sequence.toString();
  }

  /**
   * Collapses groups of matching characters exactly as {@link #collapseFrom} does, except that
   * groups of matching BMP characters at the start or end of the sequence are removed without
   * replacement.
   */
  public String trimAndCollapseFrom(CharSequence sequence, char replacement) {