§1. In addition to the things enumerated in can. 1504, the libellus which introduces the litigation must: 1/ set forth briefly, completely, and clearly the facts on which the requests of the petitioner are based; 2/ indicate the proofs by which the petitioner intends to demonstrate the facts but which cannot be presented at once, in such a way that the judge can collect them immediately.
§2. The documents on which the petition is based must be attached to the libellus, at least in an authentic copy.
Source: Code of Canon Law (Vatican.va)