Columbia subject headings:
Liturgics--History--18th century--Congresses.
Liturgics--History--19th century--Congresses.
Harvard subject headings:
Catholic Church--Europe, German-speaking--Liturgy--History--Congresses.
Liturgical movement--Catholic Church--History.
Liturgics--Germany--History--18th century.
Liturgics--Germany--History--19th century.
Princeton subject headings: