property Column.GroupByFormatCell as String
Indicates the format of the cell to be displayed when the column gets grouped by.

   String A String expression that may specify HTML format and value keyword as explained bellow.  
By default, the GroupByFormatCell property is "value", which indicates the grouping value. The GroupByFormatCell property determines the format of the cell to be displayed in the grouping item, when the column gets sorted. When the control is performing a group-by operation, the Items.FormatCell(Item,Items.GroupItem(Item)) property is set on GroupByFormatCell property, where the Item is the handle of the item being added during grouping or the Item parameter of the AddGroupItem event. For instance, if you set the GroupByFormatCell property on "upper(value)" it means that the column will be displayed in uppercase, once the user group by this column.

The value keyword in the GroupByFormatCell property indicates the value to be formatted:

The expression supports cell's identifiers as follows:

This property/method supports predefined constants and operators/functions as described here.