docs: def get_day_of_month(datestring):
      """Transforms an ordinal number into plain number with padding zero.
  
      E.g. 3rd -> 03, or 12th -> 12
  
      Keyword arguments:
      datestring -- a string
  
      Returns:
      String, or None if the transformation fails
      """
      get_day = re.compile(r"\d{1,2}(st|nd|rd|th)?", re.IGNORECASE)
      day = get_day.search(datestring)
      the_day = None
  
      if day:
          if bool(re.search(r"[st|nd|rd|th]", day.group().lower())):
              the_day = day.group()[:-2]
          else:
              the_day = day.group()
          if int(the_day) < 10:
              the_day = add_zero(the_day)
  
      return str(the_day)