Why do some religious orders answer only to the Vatican?

I was told that there are some religious orders that are not under the diocese but, rather, report only to the Papal Nuncio (I think that is the correct spelling). Could you explain, or point me in the direction of resources, what this means in terms of how the orders are run or how they establish schools?

Some religious institutes are of diocesan rite and are under the bishop of the diocese in which they were founded. Others are of pontifical rite in that they are directly under the Sacred Congregation for Institutes of Consecrated Life and Societies of Apostolic Life in Rome.

Fr. VS

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