code: def _do_exit(self, cmd, args):
          
          if cmd == 'end':
              if not args:
                  return 'root'
              else:
                  self.stderr.write(textwrap.dedent('''\
                          end: unrecognized arguments: {}
                          ''')).format(args)
  
          # Hereafter, cmd == 'exit'.
          if not args:
              return True
          if len(args) > 1:
              self.stderr.write(textwrap.dedent('''\
                      exit: too many arguments: {}
                      ''')).format(args)
          exit_directive = args[0]
          if exit_directive == 'root':
              return 'root'
          if exit_directive == 'all':
              return 'all'
          self.stderr.write(textwrap.dedent('''\
                  exit: unrecognized arguments: {}
                  ''')).format(args)
docs: \
          Exit shell.
              exit | C-D          Exit to the parent shell.
              exit root | end     Exit to the root shell.
              exit all            Exit to the command line.