code: def _set_schedules(self):
          
          self.schedules = ['ReturnHeader990x', ]
          self.otherforms = []
          for sked in self.raw_irs_dict['Return']['ReturnData'].keys():
              if not sked.startswith("@"):
                  if sked in KNOWN_SCHEDULES:
                      self.schedules.append(sked)
                  else:
                      self.otherforms.append(sked)
docs: Attach the known and unknown schedules