anchor.diff:      monitors = foldl mkMonitor [] xrandrHeads;
     in concatMapStrings (getAttr "value") monitors;
   
  +
     configFile = pkgs.stdenv.mkDerivation {
       name = "xserver.conf";
   
  
positive.code:     [ pkgs.xorg.fontadobe100dpi
        pkgs.xorg.fontadobe75dpi
      ];
  
    # Just enumerate all heads without discarding XRandR output information.
    xrandrHeads = let
  
negative.code:         echo "$config" >> $out
        ''; # */
    };
  
  
    checkAgent = mkAssert (!(cfg.startOpenSSHAgent && cfg.startGnuPGAgent))
      ''
        The OpenSSH agent and GnuPG agent cannot be started both.
        Choose between `startOpenSSHAgent' and `startGnuPGAgent'.
      '';
  
    checkPolkit = mkAssert config.security.polkit.enable
      "X11 requires Polkit to be enabled (‘security.polkit.enable = true’).";
  
  
  in
  
  