docs: def reset_title(self, title, notebook_identifier):
          """Triggered whenever a notebook tab is switched in the left bar.
  
          Resets the title of the un-docked window to the format 'upper_open_tab / lower_open_tab'
  
          :param title: The name of the newly selected tab
          :param notebook: string taking one of two values 'upper' or 'lower' indicating which notebook was changed
          """
          current_title = self.get_top_widget().get_title()
          upper_title = current_title.split('/')[0].strip()
          lower_title = current_title.split('/')[1].strip()
          if notebook_identifier == 'upper':
              new_title = title + ' / ' + lower_title
          else:
              new_title = upper_title + ' / ' + title
          self['headerbar'].props.title = new_title