docs: def _contextualise(self):
          '''Determine contextual idents (cidents)'''
          # loop through hierarchy identifying unique lineages
          # TODO: gain other contextual information, not just ident
          deja_vues = []
          for rank in reversed(self.taxonomy):
              # return named clades -- '' are ignored
              clades = [e for e in self.hierarchy[rank] if e[1]]
              # print 'Rank: {0} - {1}'.format(rank, len(clades))
              # get unique lineages at this level
              uniques = [e for e in clades if len(e[0]) == 1]
              # removed those already seen
              uniques = [e for e in uniques if e[0][0].ident not in deja_vues]
              # add each to self[ident]['cident']
              for e in uniques:
                  ident = e[0][0].ident
                  self[ident]['cident'] = e[1]
                  deja_vues.append(ident)