§1. The joinder of the issue (contestatio litis) occurs when the terms of the controversy, derived from the petitions and responses of the parties, are defined through a decree of the judge.
§2. The petitions and responses of the parties, besides those in the libellus which introduces the litigation, can be expressed either in a response to the citation or in the oral declarations made before the judge; in more difficult cases, however, the judge must convene the parties to resolve the doubt or doubts which must be answered in the sentence.
§3. The decree of the judge must be communicated to the parties; unless they have already agreed to the terms, the parties can make recourse to the judge within ten days in order to change them; a decree of the judge, however, must resolve the question as promptly as possible (expeditissime).
Source: Code of Canon Law (Vatican.va)