ASPxGridView - How to implement the Select All feature for a column with ASPxCheckBox inside DataItemTemplate

This example demonstrates how to add the Select All feature to the ASPxGridView column header when ASPxCheckBox is placed to DataItemTemplate.
ASPxGridView is initialized and bound to the Northwind database in the page markup. The Discontinued column's data item and header are replaced with ASPxCheckBox. Click the CheckBox in the column header to perform a callback to the grid and set all cells of the Discontinued column to true.