public final CharMatcher matcher;
    public final String matchingChars;

    SampleMatcherConfig(String matchingChars) {
      this(CharMatcher.anyOf(matchingChars), matchingChars);
    }

    SampleMatcherConfig(CharMatcher matcher, String matchingChars) {
      this.matcher = matcher;
      this.matchingChars = matchingChars;
    }
  }