code: def dynamic_update(plot, subplot, key, overlay, items):
      
      match_spec = get_overlay_spec(overlay,
                                    wrap_tuple(key),
                                    subplot.current_frame)
      specs = [(i, get_overlay_spec(overlay, wrap_tuple(k), el))
               for i, (k, el) in enumerate(items)]
      closest = closest_match(match_spec, specs)
      if closest is None:
          return closest, None, False
      matched = specs[closest][1]
      return closest, matched, match_spec == matched
docs: Given a plot, subplot and dynamically generated (Nd)Overlay
      find the closest matching Element for that plot.