code: def add_to(self, container):
          '''
          Add the class to @container.
          '''
          if self.container:
              self.remove_from(self.container)
          container.add(selff add_to(self, container):
          '''
          Add the class to @container.
          '''
          if self.container:
              self.remove_from(self.container)
          container.add(self)
docs: Add the class to @container.