[1] Memorials are always supplanted by a coinciding solemnity, feast, Sunday, Ash Wednesday, Holy Week, or day of the Octave of Easter.
Celebrations of solemnities and feasts are distinguished from those of memorials by, for instance, recitation of the Gloria in excelsis in the Mass (an inclusion otherwise allowed only on Sundays) and the Te Deum in the Liturgy of the Hours.
The observance of memorials is integrated into the celebration of the occurring weekday (the feria) according to the norms set forth in the General Instruction of the Roman Missal (GIRM) and the Liturgy of the Hours.
[4] Celebrations of memorials occurring between 17 and 24 December and during Lent, which are then never obligatory, consist of replacing the collect of the day with that of the saint.
[9] In approximate correspondence to memorials, Pope John XXIII's 1960 Code of Rubrics spoke of "third-class feasts", as can be seen in the General Roman Calendar of 1960, and gave some of them, either permanently or on the occasions when their celebration coincided with one of higher rank, only a commemoration within the office actually celebrated.