I posted this a few days ago as part of my review of Franz Posset's book, The Real Luther. By the way, Posset is a Roman Catholic scholar.
The most interesting section of this book so far has been Posset's treatment of Luther and the Scriptures. He mentions in passing, "As an aside, on the eve of the 'Reformation' there was a canonistic tradition supporting the assertion of the supreme authority of Scripture over councils or ecclesiastical authorities"(p. 63). He then argues that the reformed friary Luther joined had Constitutions (this document is still extant). In Chapter 17 of the Augutinian's Constitutions "the following directive is given which suggests the meaning of the maxim Scripture Alone,"
[A friar] is to read the Sacred Scripture avidly, listen to it devoutly, and learn it fervently. Sacram scripturam avide legat, devote audiat et ardenter addiscat.
Posset provides a footnote for his "aside" which I plan on exploring.