anchor.diff:  
         forwarders = mkOption {
           default = config.networking.nameservers;
  +        type = types.listOf types.str;
           description = "
             List of servers we should forward requests to.
           ";
  
positive.code: 
        blockedNetworks = mkOption {
          default = [];
          description = "
            What networks are just blocked.
          ";
  
negative.code:   cfg = config.services.bind;
  
    bindUser = "named";
  
    bindZoneOptions = {
      name = mkOption {
        type = types.str;
        description = "Name of the zone.";
      };
      master = mkOption {
        description = "Master=false means slave server";
        type = types.bool;
      };
      file = mkOption {
        type = types.str;
        description = "Zone file resource records contain columns of data, separated by whitespace, that define the record.";
      };
      masters = mkOption {
        type = types.listOf types.str;
        description = "List of servers for inclusion in stub and secondary zones.";
      };
      slaves = mkOption {
        type = types.listOf types.str;
        description = "Addresses who may request zone transfers.";
        default = [];
      };
      extraConfig = mkOption {
        type = types.str;
        description = "Extra zone config to be appended at the end of the zone section.";
        default = "";
      };
    };
  
    confFile = pkgs.writeText "named.conf"
      ''
  