§1. Without prejudice to the prescript of can. 1683, a new cause for petitioning cannot be admitted at the appellate grade, not even by way of useful accumulation; consequently, the joinder of the issue can only address whether the prior sentence is to be con-firmed or revised either totally or partially.
§2. New proofs, however, are admitted only according to the norm of can. 1600.
Source: Code of Canon Law (Vatican.va)