[update] grid guides

Author: mafanya23

docs/grid/configuration.md

@@ -1183,22 +1183,22 @@ But if you need the editor to open after a single click, apply the [](grid/api/g
 Note, that it does not work for the select editor (`editorType: "select"`) and you need to use the combobox editor (`editorType:"combobox"`) if you want a drop-down list to open on the mouse click.
 :::
 
-## Summary of calculated values
+## Custom statistics in the column header/footer and spans
 
-You can get the summary of calculated values based on the columns data using the Grid API. First, you need to form a summary list on the needed level: for a [particular column](#column-summary) or for the [whole component](#grid-summary). After that, you can [get the object with the calculated values](#getting-the-summary-object) using the `getSummary()` method.
+You can form the summary of calculated values based on the columns data for a [particular column](#column-summary) or for the [whole component](#grid-summary) and render custom statistics by using the column and Grid summary in:
+    - the configuration objects of the [`text`](#headerfooter-text) and [`tooltipTemplate`](#column-headerfooter-tooltip) properties of the column header/footer 
+    - the configuration objects of the `text` and `tooltipTemplate` properties of the Grid [`spans`](#spans) property 
 
-:::info
-Use the [`dhx.methods`](helpers/data_calculation_functions.md) helper to define the default statistical functions and to create custom functions for data calculation while creating the summary list. 
-::: 
-
-The calculated values from the `summary` property of a column or Grid can be used:
-    - in the configuration objects of the [`text`](#headerfooter-text) and [`tooltipTemplate`](#column-headerfooter-tooltip) properties of the column header/footer 
-    - in the configuration objects of the `text` and `tooltipTemplate` properties of the Grid [`spans`](#spans) property
+It is also possible to [get the object with the calculated values](#getting-the-summary-object) using the `getSummary()` method.
 
 **Related sample:** [Grid. Custom totals for footer and columns](https://snippet.dhtmlx.com/jhjxjv2l)
 
 **Related sample:** [Grid. Custom totals for footer and columns with dynamic updates on edit](https://snippet.dhtmlx.com/59d6hqtm)
 
+:::info
+Use the [`dhx.methods`](helpers/data_calculation_functions.md) helper to define the default statistical functions and to create custom functions for data calculation while creating the summary list. 
+::: 
+
 ### Column summary
 
 To form a summary list that will be available at the column's level only, you should use the [`summary`](grid/api/api_gridcolumn_properties.md) configuration option of the column. The `summary` configuration option of a column can be initialized either as an *object* or as a *string*. As an object it contains calculated values set as *key:value* pairs, where the *keys* are the field names and *values* can be:

docs/grid/usage.md

@@ -477,7 +477,9 @@ grid.export.png({
 The described functionality requires PRO version of the DHTMLX Grid (or DHTMLX Suite) package.
 :::
 
-You can group row data by column values to make them more suitable for analysis. It is possible to set a predefined Grid configuration to initialize Grid with grouped data or to use the [DataCollection API](../../data_collection) for grouping Grid data. Besides, you can group Grid rows via the UI.
+You can group row data by column values to make them more suitable for analysis. The Grid row data grouping functionality allows aggregating data in a group, adjusting the appearance, order and configuration of data grouping and rendering statistics in the summary rows.
+
+It is possible to [set a predefined Grid configuration](#configuring-data-grouping) to initialize Grid with grouped data or to use the [DataCollection API](#using-datacollection-api-for-data-grouping) for grouping Grid data. 
 
 **Related sample:** [Grid. Grouping (PRO)](https://snippet.dhtmlx.com/dvqy4ewe)
 

docs/whatsnew.md

@@ -43,8 +43,8 @@ In this version TreeGrid becomes a part of Grid. Check the [Migration](migration
 	- new Grid properties: [`group`](grid/api/grid_group_config.md), [`groupable`](grid/api/grid_groupable_config.md), [`closable`](grid/api/grid_closable_config.md)
 	- new column properties: [`groupable`](grid/api/api_gridcolumn_properties.md), [`closable`](grid/api/api_gridcolumn_properties.md)
 	- new events: [`groupPanelItemClick`](grid/api/grid_grouppanelitemclick_event.md), [`groupPanelItemMouseDown`](grid/api/grid_grouppanelitemmousedown_event.md)
-- The ability to [render custom statistics in the header/footer of columns and Grid spans](grid/configuration.md#summary-of-calculated-values)
-	- the `text` and `tooltipTemplate` properties of a column and of the Grid `spans` configuration object can be set as callback functions [to render calculated summary values](grid/configuration.md#summary-of-calculated-values)
+- The ability to [render custom statistics in the header/footer of columns and Grid spans](grid/configuration.md#custom-statistics-in-the-column-headerfooter-and-spans)
+	- the `text` and `tooltipTemplate` properties of a column and of the Grid `spans` configuration object can be set as callback functions [to render calculated summary values](grid/configuration.md#custom-statistics-in-the-column-headerfooter-and-spans)
 	- new Grid property: [`summary`](grid/api/grid_summary_config.md)
 	- new method: [`getSummary()`](grid/api/grid_getsummary_method.md)
 	- new column property: [`summary`](grid/api/api_gridcolumn_properties.md)