You asked a question and I answered it with the opinion of the Holy Father on the matter.
Ad Orientem worship is the law of the Church. Right now there is nothing prohibiting a priest from celebrating facing the people but the law of the Church seems to assume that the priest is facing ad orientem while not specifically prohibiting versus populum.
Vatican II never mandated that the altars be turned around or that the priest should offer the Mass versus populum (facing the people) rather than ad orientem (towards the east). In fact, the language used in the
General Instruction of the Roman Missal
(GIRM) seems to suggest that, while facing the people may be permitted, facing the altar is the norm.
In the GIRM there are several places where the priest is instructed when to turn around and face the people implying that he is not facing the people at other times:
** 1975 GIRM (superseded by the 2002 GIRM)
** ** 107.** The priest returns to the center and, facing the people and extending then joining his hands, pronounces the invitation: <Pray, brothers and sisters>. After the people’s response, he says the prayer over the gifts with hands outstretched.
At the end the people make the acclamation: .
** 115.** After the prayer the priest genuflects, takes the eucharistic bread, and, holding it slightly above the paten while facing the people, says: . With the people he adds, once only: <Lord, I am not worthy to receive
you>.
** 122.** Then, standing at the altar or at the chair and facing the people, the priest says, with hands outstretched: . There may be a brief period of silence, unless this has been already observed immediately after communion. He
recites the prayer after communion, at the end of which the people make the response:
.
** 2002 GIRM (the current one)**
** 124.** …Then, facing the people and extending his hands, the priest greets the people, using one of the formulas indicated. The priest himself or some other minister may also very briefly introduce the faithful to the Mass of the day.
** 146.** Upon returning to the middle of the altar, the priest, facing the people and extending and then joining his hands, invites the people to pray, saying, Orate, fraters (Pray, brethren). The people rise and make their response: Suscipiat Dominus
(May the Lord accept). Then the priest, with hands extended, says the prayer over the offerings. At the end the people make the acclamation, Amen.
** 157.** When the prayer is concluded, the priest genuflects, takes the host consecrated in the same Mass, and, holding it slightly raised above the paten or above the chalice, while facing the people, says, Ecce Agnus Dei (This is the Lamb of God). With the people he adds, Domine, non sum dignus (Lord, I am not worthy).
This is not to say that celebrating the Mass versus populum is not permitted. But it is not intended to be the norm. Vatican II did not change that. And Pope Benedict seems to intend to restore Ad Orientem worship to the Church.
James