The precise origin of Mod A is controversial, with Pavia/Milan, Pisa and Bologna all being proposed.
[1] Firm evidence of ownership of the book by the Biblioteca Estense only occurs in the early nineteenth century, although a 1495 catalogue of the Este family library in Ferrara might refer to it.
[3] Excluding flyleaves and modern additions, Mod A comprises 51 parchment folios divided into five gatherings.
Most of the compositions display the intricate and complex rhythms that define ars subtilior.
Mod A is the most important source of the compositions of Matteo da Perugia, containing thirty attributed full works and two single parts by him.