docs: def reference_creators_citation(self, ref_id):
          """Return for citation the creator surnames (locally defined) and the publication year."""
          # FIXME Delayed refactoring. Use an index instead of an ID.
          index = self.reference_index(ref_id)
          creators = self.reference_creator_surnames(index)
          creator_count = len(creators)
          if creator_count == 0:
              return ""
          year = self.reference_year(index)
          if creator_count == 1:
              return "{} ({})".format(creators[0], year)
          elif creator_count == 2:
              return "{} and {} ({})".format(creators[0], creators[1], year)
          else:
              return "{} et al. ({})".format(creators[0], year)