Answer the following question: Extract the answer to the question from the following context. Question: Who are the main subjects of the passage? Context: When not celebrating Mass but still serving a liturgical function, such as the semiannual Urbi et Orbi papal blessing, some Papal Masses and some events at Ecumenical Councils, cardinal deacons can be recognized by the dalmatics they would don with the simple white mitre (so called mitra simplex).
Answer:
cardinal deacons