code: def add_item(self, fields = None):
          
          item = Item(fields)
          self.items.append(item)
          return item
docs: Add and item to the form.
  
          :Parameters:
              - `fields`: fields of the item (they may be added later).
          :Types:
              - `fields`: `list` of `Field`
  
          :return: the item added.
          :returntype: `Item`