Columbia subject headings:
Catholic Church--Liturgy--History--20th century.
Liturgics--Congresses.
Harvard subject headings:
Catholic Church--Liturgy--History--20th century.
Liturgics--Congresses.
Princeton subject headings:
Catholic Church--Liturgy--Texts--History and criticism--20th century--Congresses.
Liturgical adaptation--Catholic Church--History--Congresses.
Liturgics--Congresses.