Gallica, the "Bibliothèque numérique de la Bibliothèque national de France" provides for free download a digitalized copy of one of the rarest liturgical books of the Ambrosian Rite: "Regole d'Alcuni Capi necessarii, E più frequenti per l'osservanza delle Sacre Cerimonie, e del Canto Fermo Ambrosiano".
This is another example of proper liturgical book "of diocesan right" (see my previous post).
In this case -which is quite an Ambrosian distinctiveness- the book is entitely written in vernacular, a beautiful later Renaissance Italian.
The "Regole d'Alcuni Capi" is a sort of brief ceremonial published by Federico Cardinal Borromeo in 1622 in order -as he explains in his introductory letter "Habbiamo più volte avvertito"- to put some order into the serious matter of sacred ceremonies according to the venerable Ambrosian Rite.
... And yes, this book is still in force for the extraordinary form of the Ambrosian Rite.
To download the full book, click on "Télécharger" link at the top of the page.