anchor.diff:  
         portNumber = mkOption {
           default = 22;
  +        type = types.port;
           description = ''
             The port on which to listen for connections.
           '';
  
positive.code: 
        srpKeyExchange = mkOption {
          default = false;
          description = ''
            Whether to enable SRP key exchange and user authentication.
          '';
  
negative.code:       };
  
        subsystems = mkOption {
          type = types.listOf types.path;
          description = ''
            List of subsystem-path pairs, where the head of the pair
            denotes the subsystem name, and the tail denotes the path to
  