docs: def iter_previewers(self, previewers=None):
          """Get previewers ordered by PREVIEWER_PREVIEWERS_ORDER."""
          if self.entry_point_group is not None:
              self.load_entry_point_group(self.entry_point_group)
              self.entry_point_group = None
  
          previewers = previewers or \
              self.app.config.get('PREVIEWER_PREFERENCE', [])
  
          for item in previewers:
              if item in self.previewers:
                  yield self.previewers[item]