code: public static CharMatcher anyOf(final CharSequence sequence) {
      switch (sequence.length()) {
        case 0:
          return none();
        case 1:
          return is(sequence.charAt(0));
        case 2:
          return isEither(sequence.charAt(0), sequence.charAt(1));
        default:
          // TODO(lowasser): is it potentially worth just going ahead and building a precomputed
          // matcher?
          return new AnyOf(sequence);
      }
    }
docs: Returns a {@code char} matcher that matches any BMP character present in the given character
  sequence. Returns a bogus matcher if the sequence contains supplementary characters.