anchor.diff:  
       virtualisation.xen.qemu-package = mkOption {
         type = types.package;
  -      default = pkgs.xen;
         defaultText = "pkgs.xen";
         example = literalExample "pkgs.qemu_xen-light";
         description = ''
  
positive.code: 
      virtualisation.xen.package = mkOption {
        type = types.package;
        default = pkgs.xen;
        defaultText = "pkgs.xen";
        example = literalExample "pkgs.xen-light";
        description = ''
  
negative.code:       message = "Xen currently does not support EFI boot";
      } ];
  
      virtualisation.xen.package = mkDefault pkgs.xen;
      virtualisation.xen.qemu = mkDefault "${pkgs.xen}/lib/xen/bin/qemu-system-i386";
      virtualisation.xen.qemu-package = mkDefault pkgs.xen;
      virtualisation.xen.stored = mkDefault "${cfg.package}/bin/oxenstored";
  
      environment.systemPackages = [ cfg.package ];
  