[update] what's new for v9.1

Author: mafanya23

docs/grid/features.md

@@ -241,10 +241,11 @@ In this section you will find the ways of editing data in Grid.
 
 In this section you will find the ways of sorting data in Grid.
 
-| Topic                                                        | Description                                                                                                 |
-| ------------------------------------------------------------ | ----------------------------------------------------------------------------------------------------------- |
-| [Sorting data](../usage/#sorting-data)                       | Learn how to sort data in the grid ([Example](https://snippet.dhtmlx.com/81dmbdfd))                         |
-| [Sortable columns](../configuration/#sortable-columns)       | Learn how to define whether a column should be sortable ([Example](https://snippet.dhtmlx.com/r3prvlmo))    |
+| Topic     									| Description                                                      |
+| --------------------------------------------- | ---------------------------------------------------------------- |
+| [Sorting data](../usage/#sorting-data)        | Learn how to sort data in the grid ([Example](https://snippet.dhtmlx.com/81dmbdfd))                |
+| [Sorting by multiple columns](../usage/#sorting-by-multiple-columns)   | Learn how to sort Grid data by multiple columns ([Example 1](https://snippet.dhtmlx.com/4ej0i3qi), [Example 2](https://snippet.dhtmlx.com/786zr190))                |
+| [Sortable columns](../configuration/#sortable-columns)| Learn how to define whether a column should be sortable ([Example](https://snippet.dhtmlx.com/r3prvlmo))    |
 | [Getting sorting state](../usage/#getting-the-sorting-state) | Learn how to get the current state of sorting data in Grid ([Example](https://snippet.dhtmlx.com/u2vk3ri3)) |
 
 ### How to filter data

docs/whatsnew.md

@@ -12,6 +12,12 @@ Before updating DHTMLX to the latest version, please check the [Migration to New
 
 Released on February 18, 2025
 
+<a href="https://dhtmlx.com/blog/dhtmlx-suite-9-1/" target="_blank">Review of the release on the blog</a>
+
+### Breaking changes
+
+This version brings some updates in the API methods. Check the [Migration](migration.md#90---91) guide to keep in step with the latest updates.
+
 ### New functionality
 
 #### Common features
@@ -20,18 +26,21 @@ Released on February 18, 2025
 
 #### Grid 
 
-- Row expander with the possibility to insert any Suite widget or HTML content (PRO version)
-- Multi-sorting functionality that allows sorting Grid by several columns (PRO version)
+- [Row expander](grid/configuration.md#row-expander) with the possibility to insert any Suite widget or HTML content (PRO version)
+- [Multi-sorting](grid/usage.md#sorting-by-multiple-columns) functionality that allows sorting Grid by several columns (PRO version)
 
 ### Updates
 
 #### Grid
 
-- Improved export functionality by using the **json2excel** export module
+- Improved and extended export to Excel functionality 
 
 ### Fixes
 
+- DataCollection. The `sort()` method called without arguments doesn't reset the applied sorting 
+- Grid. Falsy firing of data events on row drag-n-drop
 - Toolbar. Menu wrong item positioning
+- TreeCollection. The `restoreOrder()` method doesn't reset the applied sorting
 
 ### New samples