code: def add(self, value_id, name, value_class):
          
          item = value_class(
              name,
              value_id=self.controller.component_id + "." + value_id,
              is_input=self.is_input,
              index=self.count,
              spine = self.controller.spine
          )
  
          #if self._inject and self.controller:
          #    setattr(self.controller, value_id, item)
          #setattr(self, value_id, item)
  
          self.count += 1
          self._items[value_id] = item
          if self.is_input and self.controller:
              item.add_observer(self.controller)
          return item
docs: Factory function that creates a value.
  
          :param value_id: id of the value, used to reference the value within this list.BaseException
  
          :param value_class: The class of the value that should be created with this function.