code: def action_checkbox(self, obj):
          
          if self.check_concurrent_action:
              return helpers.checkbox.render(helpers.ACTION_CHECKBOX_NAME,
                                             force_text("%s,%s" % (obj.pk,
                                                                   get_revision_of_object(obj))))
          else:  # pragma: no cover
              return super(ConcurrencyActionMixin, self).action_checkbox(obj)
docs: A list_display column containing a checkbox widget.