Sometimes when an object gets selected, you want to make it look like another object is what really got selected. Normally this happens for groups, where you don't want to have selection handles on the whole group, but only on some particular child object. This property allows you to specify which object should get selection handles when this object gains selection. The default value is this object itself. The selection object's CanResize method will control if that object gets resize selection handles and if the user can actually resize that object. You should be careful to make sure the value of this property is not confusing to the user. Returning unrelated or varying objects may produce indeterminate behavior.

Reference

GoObject Class
GoObject Members
OnGotSelection Method
AddSelectionHandles Method