anchor.diff:  
     cfg = config.services.dbus;
   
  -  inherit (pkgs) dbus;
  -
     homeDir = "/var/run/dbus";
   
     configDir = pkgs.stdenv.mkDerivation {
  
positive.code: 
      security.setuidOwners = singleton
        { program = "dbus-daemon-launch-helper";
          source = "${dbus}/libexec/dbus-daemon-launch-helper";
          owner = "root";
          group = "messagebus";
          setuid = true;
  
negative.code:     buildCommand = ''
        ensureDir $out
        
        cp -v ${pkgs.dbus_daemon}/etc/dbus-1/system.conf $out/system.conf
  
        # !!! Hm, these `sed' calls are rather error-prone...
  
  