code: function updateGroup(oContext) {
  			var oNewGroup = oBinding.getGroup(oContext);
  			if (oNewGroup.key !== sGroup) {
  				var oGroupHeader;
  				//If factory is defined use it
  				if (oBindingInfo.groupHeaderFactory) {
  					oGroupHeader = oBindingInfo.groupHeaderFactory(oNewGroup);
  				}
  				that[sGroupFunction](oNewGroup, oGroupHeader);
  				sGroup = oNewGroup.key;
  			}
  		}
docs: Check the current context for its group. If the group key changes, call the group function on the control.