§1. After having received the petition and heard the parties, the judge is to decide as promptly as possible (expeditissime) whether the proposed incidental question seems to have a foundation and a connection with the principal trial or rather must be rejected at the outset. If the judge admits the incidental question, the judge is to decide whether it is of such gravity that it must be resolved by an interlocutory sentence or by a decree.
§2. If the judge decides not to resolve the incidental question before the definitive sentence, however, the judge is to decree that the question will be considered when the principal case is decided.
Source: Code of Canon Law (Vatican.va)