code: def start(self):
          
          if self.extra_args:
              sys.exit('{} takes no extra arguments'.format(self.name))
          else:
  
              if self._toggle_value:
                  nbextensions.install_nbextension_python(
                      _pkg_name, overwrite=True, symlink=False,
                      user=self.user, sys_prefix=self.sys_prefix, prefix=None,
                      nbextensions_dir=None, logger=None)
              else:
                  nbextensions.uninstall_nbextension_python(
                      _pkg_name, user=self.user, sys_prefix=self.sys_prefix,
                      prefix=None, nbextensions_dir=None, logger=None)
  
              self.toggle_nbextension_python(_pkg_name)
              self.toggle_server_extension_python(_pkg_name)
docs: Perform the App's actions as configured.