@Override
    public String toString() {
      return "CharMatcher.and(" + first + ", " + second + ")";
    }
  }

  /** Implementation of {@link #or(CharMatcher)}. */
  private static final class Or extends CharMatcher {

    final CharMatcher first;
    final CharMatcher second;

    Or(CharMatcher a, CharMatcher b) {
      first = checkNotNull(a);
      second = checkNotNull(b);