code: def get_mark_char(char):
      
      char = accent.remove_accent_char(char.lower())
      if char == "":
          return Mark.NONE
      if char == "đ":
          return Mark.BAR
      if char in "ă":
          return Mark.BREVE
      if char in "ơư":
          return Mark.HORN
      if char in "âêô":
          return Mark.HAT
      return Mark.NONE
docs: Get the mark of a single char, if any.