4 Means should be taken therefore in every part of the world for the protection and advancement of all the individual Churches and, to this end, there should be established parishes and a special hierarchy where the spiritual good of the faithful demands it. The hierarchs of the different individual Churches with jurisdiction in one and the same territory should, by taking common counsel in regular meetings, strive to promote unity of action and with common endeavor to sustain common tasks, so as better to further the good of religion and to safeguard more effectively the ordered way of life of the clergy. All clerics and those aspiring to sacred Orders should be instructed in the rites and especially in the practical norms that must be applied in interritual questions. The laity, too, should be taught as part of its catechetical education about rites and their rules. Finally, each and every Catholic, as also the baptized of every non-Catholic church or denomination who enters into the fullness of the Catholic communion, must retain his own rite wherever he is, must cherish it and observe it to the best of his ability , without prejudice to the right in special cases of persons, communities or areas, to have recourse to the Apostolic See, which, as the supreme judge of interchurch relations, will, acting itself or through other authorities, meet the needs of the occasion in an ecumenical spirit, by the issuance of opportune directives, decrees or rescripts.
Source: Orientalium Ecclesiarum (Vatican.va)