"I have stated the principle as being a self-imposed limitation upon the state's sovereign authority and I must clarify this concept by distinguishing certain other cases relied upon by Mr McDonald. First, I am not concerned with the enforcement of private rights arising out of matters properly subject to the jurisdiction of the court. For example, a foreigner may have agreed by a contract over which the court has jurisdiction to perform various acts abroad. There can be no objection in principle to enforcement of those rights by injunction or specific performance, even though this requires the performance of acts abroad."