A long expression that indicates the item's index.
The Index property gets the index of the Item object in
items collection of the owner group. Use the Position
property to change the item's position. The Index property is allocated when
the items is added to the group's list, using the AddItem
method. Use the Item property to access an item
giving its index of by its caption. Use the Caption
property to specify the caption of the item. Use the Image
property to assign a picture to an item.