Columbia subject headings:
Catholic Church--Liturgy.
Gregorian chants--History and criticism.
Manuscripts, Medieval.
Harvard subject headings:
Catholic Church--Liturgy--Sources.
Gregorian chants--History and criticism--Sources.
Music--500-1400--History and criticism--Sources.
Princeton subject headings:
Catholic Church--Liturgy.
Gregorian chants--History and criticism.
Manuscripts, Medieval.