code: func (q Quad) GetString(d Direction) string {
  	switch d {
  	case Subject:
  		return StringOf(q.Subject)
  	case Predicate:
  		return StringOf(q.Predicate)
  	case Object:
  		return StringOf(q.Object)
  	case Label:
  		return StringOf(q.Label)
  	default:
  		panic(d.String())
  	}
  }
docs: // Per-field accessor for quads that returns strings instead of values.