docs: function (order) {
              var ret = order;
              if (order) {
                  ret = order.map(function (o) {
                      if (isInstanceOf(o, OrderedExpression)) {
                          return o.invert();
                      } else {
                          return new OrderedExpression(isString(o) ? new Identifier(o) : o);
                      }
                  }, this);
              }
              return ret;
          }