code: @Cached
      @DontLabel
      public Rule ignoreCase(final char c)
      {
          return Character.isLowerCase(c) == Character.isUpperCase(c)
              ? ch(c) : new CharIgnoreCaseMatcher(c);
      }
docs: Match a given character in a case-insensitive manner
  
  @param c the character to match
  @return a rule