assertEqualsSame(expected, in, is('-').trimAndCollapseFrom(in, replacement));
      assertEqualsSame(expected, in, is('-').or(is('#')).trimAndCollapseFrom(in, replacement));
      assertEqualsSame(expected, in, isNot('x').trimAndCollapseFrom(in, replacement));
      assertEqualsSame(expected, in, is('x').negate().trimAndCollapseFrom(in, replacement));

      assertEqualsSame(expected, in, is('-').trimAndCollapseFrom(in, replacement));
      assertEqualsSame(expected, in, is('-').or(is('#')).trimAndCollapseFrom(in, replacement));
      assertEqualsSame(expected, in, isNot('x').trimAndCollapseFrom(in, replacement));
      assertEqualsSame(expected, in, is('x').negate().trimAndCollapseFrom(in, replacement));

   * groups of matching BMP characters at the start or end of the sequence are removed without
   * replacement.
   */
  public String trimAndCollapseFrom(CharSequence sequence, char replacement) {
    // This implementation avoids unnecessary allocation.
    int len = sequence.length();
    int first = 0;
    int last = len - 1;