code: def order(self, mechanism, purview):
          
          if self is Direction.CAUSE:
              return purview, mechanism
          elif self is Direction.EFFECT:
              return mechanism, purview
  
          from . import validate
          return validate.direction(self)
docs: Order the mechanism and purview in time.
  
          If the direction is ``CAUSE``, then the purview is at |t-1| and the
          mechanism is at time |t|. If the direction is ``EFFECT``, then the
          mechanism is at time |t| and the purview is at |t+1|.