docs: def add_accent_char(char, accent):
      """
      Add accent to a single char.  Parameter accent is member of class
      Accent
      """
      if char == "":
          return ""
      case = char.isupper()
      char = char.lower()
      index = utils.VOWELS.find(char)
      if (index != -1):
          index = index - index % 6 + 5
          char = utils.VOWELS[index - accent]
      return utils.change_case(char, case)