docs: def action(args):
      """Roll back commands on a refpkg.
  
      *args* should be an argparse object with fields refpkg (giving the
      path to the refpkg to operate on) and n (giving the number of
      operations to roll back).
      """
      log.info('loading reference package')
  
      r = refpkg.Refpkg(args.refpkg, create=False)
  
      # First check if we can do n rollbacks
      q = r.contents
      for i in range(args.n):
          if q['rollback'] is None:
              log.error('Cannot rollback {} changes; '
                        'refpkg only records {} changes.'.format(args.n, i))
              return 1
          else:
              q = q['rollback']
  
      for i in range(args.n):
          r.rollback()
  
      return 0