The Papal Magisterium

Where in Vatican I does it say that it (along with infallibility) is limited to certain document types written by the bishop of Rome, or that certain formulae must be used to signal that it is ex cathedra?

Let's not forget that Francis believes even the things he says to the media are part of his magisterium: https://t.co/pw5uOm0v2n @CMReport

— Steve Skojec (@SteveSkojec) October 21, 2020