In addition to displaying summaries/results from aggregates in the group header,     RadGrid exposes group footers feature which provides the option to render footer under each group in the grid.     The type of this footer item is GridGroupFooterItem. To enable     this functionality merely set the ShowGroupFooter property of the     respective GridTableView instance to true (its default value is false). 
	RadGrid also gives you the opportunity to retain the visibility of the group footers when their corresponding     group header row is collapsed. In order to switch on this feature, just set the     GroupingSettings.RetainGroupFooterVisibilityproperty to true.         
	The group footers are most commonly used to visualize calculations from aggregate functions within     the scope of the current group. Furthermore, with nested groups you will have group     footer for each inner group along with one for the main group. Aggregate calculations     are supported for GridBoundColumns, GridCalculatedColumns and GridTemplateColumns. 
	In order to specify how the group aggregates will be evaluated, specify in every     GridBoundColumn/GridCalculatedColumn/GridTemplateColumn the Aggregate property which     accepts values from the GridAggregateFunction enumeration.
		
		RadGrid will calculate aggregates over the entire data source and will respect the     filter expression applied (if present).