code: public static CharPredicate among(final String chars) {
      return new CharPredicate() {
        @Override public boolean isChar(char c) {
          return chars.indexOf(c) >= 0;
        }
        @Override public String toString() {
          return '[' + chars + ']';
        }
      };
    }
docs: A {@link CharPredicate} that returns true if the character is equal to any character in
  {@code chars}.