sentences:  Before the 15th century, most musical settings of the Ordinary of the Mass were grouped according to movement.For instance, the Ivrea Codex and Apt Codex both contain mass movements, and these movements are grouped so that all of the Kyries are together, all of the Glorias are together, and so on.A priest selecting the music for the service would choose one from each group to be sung, and so any setting of a movement could be used in combination with any other.