anchor.diff:  
       ${if videoDriver == "nvidia"
         then "env XORG_DRI_DRIVER_PATH=${nvidiaDrivers}/X11R6/lib/modules/drivers/"
  -      else if cfg.driSupport
  +    else if cfg.driSupport
         then "env XORG_DRI_DRIVER_PATH=${mesa}/lib/modules/dri"
         else ""
       } 
  
positive.code:   cfg = config.services.xserver;
  
    optional = condition: x: if condition then [x] else [];
  
    #Beryl parameters
    #berylcore
    #berylmanager
    #berylemerald
  
    # Get a bunch of user settings.
    videoDriver = cfg.videoDriver;
  
negative.code:   ++ optional (windowManager == "compiz") [
      compiz
    ]
    ++ optional (sessionType == "xterm") [
      xterm
    ]
  