code: def add(self, actors):
          
          if utils.isSequence(actors):
              for a in actors:
                  if a not in self.actors:
                      self.actors.append(a)
              return None
          else:
              self.actors.append(actors)
              return actors
docs: Append input object to the internal list of actors to be shown.
  
          :return: returns input actor for possible concatenation.