"Preachers shall behave themselves modestly and soberly in every department of their life. But especially shall they see to it that they teach nothing in the way of a sermon, which they would have religiously held and believed by the people, save what is agreeable to the teaching of the Old or New Testament, AND what the Catholic fathers and ancient bishops have collected from this selfsame doctrine." - Canon 6, Convocation of 1571, Church of England
It seems that this canon prevents using Article VI in such a way as to allow exegesis that is untethered to the previous exegetical work of the Catholic fathers. In other words, Anglican clergymen are not permitted to be like Presbyterians, Baptists and free-church Evangelicals, where everyone in effect becomes his own pope.
An Anglo-Catholic priest shared this canon with a bunch of "Reformation Anglicans" on a Facebook discussion page, when a number of them were arguing against the doctirne of the perpetual virginity of Mary. You should have heard all the heads exploding, since this was a canon that dated back to the Edwardian and early Elizabethan phases of the English Reformation. I complemented this by asking the question of which Anglican divines, prior to modern times, ever denied this doctrine. Both the priest and I were soon disinvited to this particular Facebook page, for this challenge and for pointing out related pathologies of Realignment Anglicanism in general, and in the Anglican Church in North America (ACNA) in particular.