docs: def _work_chain_mod_time(self, worker_name):
          """ Internal: We compute a modification time of a work chain.
              Returns:
                  The newest modification time of any worker in the work chain. 
          """
  
          # Bottom out on sample, info or tags
          if worker_name=='sample' or worker_name=='info' or worker_name=='tags':
              return datetime.datetime(1970, 1, 1)
  
          my_mod_time = self._get_work_results('info', worker_name)['info']['mod_time']
          dependencies = self.plugin_meta[worker_name]['dependencies']
          if not dependencies:
              return my_mod_time
          else:
              depend_mod_times = [my_mod_time]
              for depend in dependencies:
                  depend_mod_times.append(self._work_chain_mod_time(depend))
              return max(depend_mod_times)