In this chapter, the author reveals his admiration for the teaching and published work of Timothy J. McGee, who has inspired him, and innumerable other students and scholars. Traditional rubrics in medieval liturgical books are fairly clear-cut in their intent: they are ritual or ceremonial directions, ranging from the short and mundane to the very detailed and wide-ranging, such as the rubrica magna placed in breviaries after Trinity. The author discusses the rubrics found in Tr93 and Tr90, which range from the mundane to the perplexing, and evaluate their possible interpretations for the performers of the music. Tr93 is one of the most important sources of polyphonic music of the mid-fifteenth century in terms of the sheer number of complete musical works it contains, its generally clear organization, legible notation and the favourable state in which it has been preserved.