code: def get_placeholders(self, format_string):
          
          placeholders = set()
          # Tokenize the format string and process them
          for token in self.tokens(format_string):
              if token.group("placeholder"):
                  placeholders.add(token.group("key"))
              elif token.group("command"):
                  # get any placeholders used in commands
                  commands = dict(parse_qsl(token.group("command")))
                  # placeholders only used in `if`
                  if_ = commands.get("if")
                  if if_:
                      placeholders.add(Condition(if_).variable)
          return placeholders
docs: Parses the format_string and returns a set of placeholders.