code: def add(self, item, position=5):
          
          if item in self.items:
              return
          self.items[item] = position
          self._add_dep(item)
          self.order = None
          self.changed(code_changed=True)
docs: Add an item to the list unless it is already present.
          
          If the item is an expression, then a semicolon will be appended to it
          in the final compiled code.