question: public void attachToMovingGrabPoint ( OffsetGrabPoint gp ) { gp . addGrabPoint ( gpo ) ; }
target:  Attach to the Moving OffsetGrabPoint so if it moves, it will move this EditableOMGraphic with it. EditableOMGraphic version doesn't do anything, each subclass has to decide which of its OffsetGrabPoints should be attached to it.