anchor.diff:        description = "Use a development snapshot of SANE scanner drivers.";
       };
   
  +    hardware.sane.extraBackends = mkOption {
  +      type = types.listOf types.path;
  +      default = [];
  +      description = "Packages providing extra SANE backends to enable.";
  +    };
  +
     };
   
   
  
positive.code: let
  
    pkg = if config.hardware.sane.snapshot then pkgs.saneBackendsGit else pkgs.saneBackends;
  
  in
  
  
negative.code: 
    config = mkIf config.hardware.sane.enable {
  
      environment.systemPackages = backends;
      environment.variables = {
        SANE_CONFIG_DIR = "${saneConfig}/etc/sane.d";
        LD_LIBRARY_PATH = [ "${saneConfig}/lib/sane" ];
      };
      services.udev.packages = backends;
  
      users.extraGroups."scanner".gid = config.ids.gids.scanner;
  
  