docs: def _attach_subcommands(self):
          """Create a subparser and add the registered commands to it.
  
          This will also call ``_init`` on each subcommand (in turn invoking its
          ``_attach_subcommands`` method).
          """
          if self.subcommands:
              self.subparsers = self.parser.add_subparsers()
  
              for subcommand in self.subcommands:
                  subparser = self.subparsers.add_parser(subcommand.name,
                                                         help=subcommand.title)
                  if subcommand.handler:
                      self._register_handler(subparser, subcommand.handler)
                  subcommand._init(subparser)