docs: def INDEX_OF_BYTES(string_expression, substring_expression, start=None, end=None):
      """
      Searches a string for an occurence of a substring and returns the UTF-8 byte index (zero-based) of the first occurence.
      If the substring is not found, returns -1.
      https://docs.mongodb.com/manual/reference/operator/aggregation/indexOfBytes/
      for more details
      :param string_expression: The string or expression of string
      :param substring_expression: The string or expression of substring
      :param start: An integral number (or expression) that specifies the starting index position for the search.
      :param end: An integral number (or expression) that specifies the ending index position for the search.
      :return: Aggregation operator
      """
      res = [string_expression, substring_expression]
      if start is not None:
          res.append(start)
      if end is not None:
          res.append(end)
      return {'$indexOfBytes': res}