docs: def to_string(comp_type):
      '''Returns the correct string for a given composite type.
  
      @raises InvalidCompositeTypeError
  
      '''
      if comp_type == NONE:
          return NONE
      elif comp_type== PERIODIC_EC_SHARED:
          return PERIODC_EC_SHARED
      elif comp_type == PERIODIC_STATE_SHARED:
          return PERIODIC_STATE_SHARED
      elif comp_type == GROUPING:
          return GROUPING
      elif comp_type == FSM_EC_SHARED:
          return FSM_EC_SHARED
      elif comp_type == FSM_STATE_SHARED:
          return FSM_STATE_SHARED
      else:
          raise InvalidCompositeTypeError(type_string)