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