code: @Cached
      @DontLabel
      public Rule string(final char... characters)
      {
          if (characters.length == 1)
              return ch(characters[0]); // optimize one-char strings
          return new StringMatcher(new String(characters));
      }
docs: Match a given set of characters as a string literal
  
  @param characters the characters of the string to match
  @return a rule