code: def mark_seen(self):
          
          data = self.get_selected_item()
          if data['is_new']:
              with self.term.loader('Marking as read'):
                  data['object'].mark_as_read()
              if not self.term.loader.exception:
                  data['is_new'] = False
          else:
              with self.term.loader('Marking as unread'):
                  data['object'].mark_as_unread()
              if not self.term.loader.exception:
                  data['is_new'] = True
docs: Mark the selected message or comment as seen.