Selection.PrimaryItem Property (Visio)
Returns the Shape object that is a Selection object's primary item. Read-only.
In a drawing window, the primary selected item is shown with green selection handles and non-primary selected items are shown with blue selection handles. The outcome of some operations is affected by which selected item is the primary item. For example, the Align Shapes command aligns non-primary selected items with the primary selected item.
If a Selection object contains no Shape objects, or the primary Shape object is one that isn't enumerated given the Selection object's IterationMode property, the PrimaryItem property returns Nothing and raises no exception.