Canon 350. §1 The College of Cardinals is divided into three orders: the episcopal order, to which belong those Cardinals to whom the Roman Pontiff assigns the title of a suburbicarian Church, and eastern-rite Patriarchs who are made members of the
College of Cardinals; the presbyteral order, and the diaconal order.

§2 Cardinal priests and Cardinal deacons are each assigned a title or a deaconry in
Rome by the Roman Pontiff.
[NB see Rescript “ex audientia Ss.mi” of 26 June 2018 by which four Cardinals were coopted into the Order of Bishops and made equivalent to Cardinals who hold the title of a suburbicarian Church, in derogation of can. 350 §§1-2 and 352 §§2-3
(Communicationes 50 (2018), pp. 431-432).]

§3 Eastern Patriarchs within the College of Cardinals have their patriarchal see as a title.

§4 The Cardinal Dean has the title of the diocese of Ostia, together with that of any other Church to which he already has a title.

§5 By a choice made in Consistory and approved by the Supreme Pontiff, Cardinal priests may transfer to another title; Cardinal deacons may transfer to another deaconry and, if they have been a full ten years in the diaconal order, to the presbyteral order: priority of order and of promotion is to be observed.

§6 A Cardinal who by choice transfers from the diaconal to the presbyteral order, takes precedence over all Cardinal priests who were promoted to the Cardinalate after him.