code: def _add_command(parser, subparser_fn, handler, cell_required=False,
                   cell_prohibited=False):
    
    sub_parser = subparser_fn(parser)
    sub_parser.set_defaults(func=lambda args, cell: _dispatch_handler(
        args, cell, sub_parser, handler, cell_required=cell_required,
        cell_prohibited=cell_prohibited))
docs: Create and initialize a pipeline subcommand handler.