Columbia subject headings:
Catholic Church--Liturgy--History.
Liturgics.
Harvard subject headings:
Catholic Church--Liturgy--Congresses.
Catholic Church--Liturgy--History--Sources.
Catholic Church--Liturgy--History.
Liturgics--History--Middle Ages, 600-1500--Sources.
Princeton subject headings:
Catholic Church--Liturgy--Congresses.
Catholic Church--Liturgy--History--Congresses.