docs: function flatten() {
      var arr = [];
      for (var _i = 0; _i < arguments.length; _i++) {
          arr[_i] = arguments[_i];
      }
      var i = 0;
      var result = [];
      while (i < arr.length) {
          var itm = arr[i];
          if (is_1.isArray(itm))
              result = result.concat(flatten.apply(void 0, itm));
          else
              result = result.concat([itm]);
          i++;
      }
      return result;
  }