anchor.diff:          environment.etc."bird/${variant}.conf".source = pkgs.writeTextFile {
             name = "${variant}.conf";
             text = cfg.config;
  -          checkPhase = ''
  +          checkPhase = optionalString cfg.checkConfig ''
               ${pkg}/bin/${birdBin} -d -p -c $out
             '';
           };
  
positive.code:               <link xlink:href='http://bird.network.cz/'/>
              '';
            };
          };
        };
  
  
negative.code: { config, lib, pkgs, ... }:
  
  let
    inherit (lib) mkEnableOption mkIf mkOption optionalString types;
  
    generic = variant:
      let
  