anchor.diff:  
         user = mkOption {
           default = "firebird";
  +        type = types.str;
           description = ''
             User account under which firebird runs.
           '';
  
positive.code: 
        port = mkOption {
          default = "3050";
          description = ''
            Port Firebird uses.
          '';
  
negative.code: 
        baseDir = mkOption {
          default = "/var/db/firebird"; # ubuntu is using /var/lib/firebird/2.1/data/.. ?
          type = types.str;
          description = ''
            Location containing data/ and system/ directories.
            data/ stores the databases, system/ stores the password database security2.fdb.
  