property Items.GroupItem (Item as HITEM) as Long
Indicates a group item if positive, and the value specifies the index of the column that has been grouped.

TypeDescription
Item as HITEM A Long expression that specifies the handle of the item being queried
Long A Long expression that specifies index of the column being grouped, or a negative value if the item is a regular item, not a grouping item. 
The GroupItem method determines the index of the column that indicates the column being grouped. In other words, the CellCaption(Item,GroupItem(Item) ) gets the default caption to be displayed for the grouping item. The Ungroup method removes all grouping items. For instance, when a column gets grouped by, the control sorts by that column, collects the unique values being found, and add a new item for each value found, by adding the items of the same value as children. The ( ViewItemUpdate(exAddGroupItem) event is fired for each new item to be inserted in the Items collection during the grouping.