The plus/minus graphic is an optional graphic, which indicates the current expand status of an item. Three graphics can be defined, one for a (non-expandable) leaf item (Items.PlusMinusImageLeaf), one for an expanded parent item (Items.PlusMinusImageExpanded) and one for a non-expanded parent item (Items.PlusMinusImageExpandable), all of the same size. All items share the same three graphics and based on the expand status, the appropriate graphic is displayed. Individual items cannot override the graphic used.