code: def __replace_displayed_display_item(self, display_panel, display_item, d=None) -> Undo.UndoableCommand:
          
          self.document_controller.replaced_display_panel_content = display_panel.save_contents()
          command = DisplayPanel.ReplaceDisplayPanelCommand(self)
          if display_item:
              display_panel.set_display_panel_display_item(display_item, detect_controller=True)
          elif d is not None:
              display_panel.change_display_panel_content(d)
          display_panel.request_focus()
          self.__sync_layout()
          return command
docs: Used in drag/drop support.