anchor.diff:          type = types.path;
           default = "${cfg.dataDir}/playlists";
           defaultText = ''''${dataDir}/playlists'';
  +        apply = toString;       # Prevent copies to Nix store.
           description = ''
             The directory where mpd stores playlists.
           '';
  
positive.code:         type = types.path;
          default = "${config.home.homeDirectory}/music";
          defaultText = "$HOME/music";
          description = ''
            The directory where mpd reads music from.
          '';
  
negative.code:         type = types.path;
          default = "${config.xdg.dataHome}/${name}";
          defaultText = "$XDG_DATA_HOME/mpd";
          apply = toString;       # Prevent copies to Nix store.
          description = ''
            The directory where MPD stores its state, tag cache,
            playlists etc.
  