In any proceeding in a court subject to these rules in which an Act of Assembly is alleged to be unconstitutional or a charitable bequest or trust is involved and the Commonwealth is not a party, the party raising the question of constitutionality or the plaintiff in a proceeding involving a charitable bequest or trust shall promptly give notice thereof by registered mail to the Attorney General of Pennsylvania together with a copy of the pleading or other portion of the record raising the issue and shall file proof of the giving of the notice. The Attorney General may intervene as a party or may be heard without the necessity of intervention. The court in its discretion may stay the proceedings pending the giving of the notice and a reasonable opportunity to the Attorney General to respond thereto. If the circumstances of the case require the court may proceed without prior notice in which event notice shall be given as soon as possible; or the court may proceed without waiting action by the Attorney General in response to a notice.