Caraffa, I addressed the quotation from Pope St. Leo the Great this morning.
Take a look, page 4 of this thread, posted at 7:59 am.
Ah, but when a Pope issues a dogmatic statement addressing a certain point, outside points mentioned in that same letter or Bull cannot be heretical, only possibly erroneous. Usually these outside points fall into at the very least two theological categories:
Doctrina catholica-Catholic Doctrine-things taught by Popes or a very high majority of Doctors, Saints, theologians, though not always infallibly. If a doctrine is in this category it cannot change.
Theologica certa-Theologically Certain-a Doctrine which has connection to divine revelation or revealed dogma or is contained within the revealed dogma. Theological schools prior to the rise of progessivism/modernism taught it as such.