“Taking conciliar custom into consideration and also the pastoral purpose of the present Council, the sacred Council defines as binding on the Church only those things in matters of faith and morals which it shall openly declare to be binding. The rest of the things which the sacred Council sets forth, inasmuch as they are the teaching of the Church’s supreme magisterium, ought to be accepted and embraced by each and every one of Christ’s faithful according to the mind of the sacred Council. The mind of the Council becomes known either from the matter treated or from its manner of speaking, in accordance with the norms of theological interpretation.”
From the “Preliminary Note” to Lumen Gentium, the so-called “Dogmatic Constitution” of the Church.
In other words, if the Church previously defined it as dogmatic, it’s dogmatic. If it’s new with Vatican II, it’s not dogmatic, but they’d really, really like it if we accept it.
“The truth is that this particular Council defined no dogma at all, and deliberately chose to remain on a modest level, as a merely pastoral council; and yet many treat it as though it had made itself into a sort of superdogma which takes away the importance of all the rest.”
Oddly enough, the “Nota Previa” which contains this passage is not in the Vatican website’s text of _Lumen Gentium_ and is extremely hard to find online. Seems to be something that they don’t want publicized.