code: def get_tab_title(key, frame, overlay):
      
      if isinstance(overlay, Overlay):
          if frame is not None:
              title = []
              if frame.label:
                  title.append(frame.label)
                  if frame.group != frame.params('group').default:
                      title.append(frame.group)
              else:
                  title.append(frame.group)
          else:
              title = key
          title = ' '.join(title)
      else:
          title = ' | '.join([d.pprint_value_string(k) for d, k in
                              zip(overlay.kdims, key)])
      return title
docs: Computes a title for bokeh tabs from the key in the overlay, the
      element and the containing (Nd)Overlay.