The French Organ Mass is a classic example of the so-called "alternatim" practice, a term which indicates a type of liturgy when alternate sections of liturgical items (such as a Mass or a Magnificat) were performed by different forces. In organ "alternatim" practice—and so, in the French Organ Mass—the organist plays when texts would otherwise have been sung. The tradition stemmed from the antiphonal psalmody of the early Western church. In France, organ playing was regulated by printed "ceremonials", which specified precisely when the organist should play. The surviving ceremonials are all similar in outline, but differ widely in details. A typical organ Mass comprised versets for the ordinary of the Mass except for the Credo (which was to be sung in its entirety).