code: def find_link(cls, plot, link=None):
          
          registry = Link.registry.items()
          for source in plot.link_sources:
              if link is None:
                  links = [
                      l for src, links in registry for l in links
                      if src is source or (src._plot_id is not None and
                                           src._plot_id == source._plot_id)]
                  if links:
                      return (plot, links)
              else:
                  if ((link.target is source) or
                      (link.target is not None and
                       link.target._plot_id is not None and
                       link.target._plot_id == source._plot_id)):
                      return (plot, [link])
docs: Searches a GenericElementPlot for a Link.