Canon 144. §1 In common error, whether of fact or of law, and in positive and probable doubt, whether of law or of fact, the Church supplies executive power of governance for both the external and the internal forum.

§2 The same norm applies to the faculties mentioned in cann. 883, 966, and 1111 §1.

Canon 1127. §1 The prescripts of can. 1108 are to be observed for the form to be employed in a mixed marriage; if however a Catholic party contracts marriage with a non-Catholic party of an Eastern Rite, the canonical form of the celebration must be observed for liceity only; for validity, however, the presence of a priest is required notwithstanding whatever else is to be observed in accordance with the law.
[revised wording according to m.p. De concordia inter Codices, 31.V.2016]

§2 If there are grave difficulties in the way of observing the canonical form, the local
Ordinary of the catholic party has the right to dispense from it in individual cases, having however consulted the Ordinary of the place of the celebration of the marriage; for validity, however, some public form of celebration is required. It is for the Episcopal Conference to establish norms whereby this dispensation may be granted in a uniform manner.

§3 It is forbidden to have, either before or after the canonical celebration in accordance with §1, another religious celebration of the same marriage for the purpose of giving or renewing matrimonial consent. Likewise, there is not to be a religious celebration in which the catholic assistant and a non-catholic minister, each performing his own rite, ask for the consent of the parties.