“We wish therefore and prescribe, that all observe the law of the Church, and that at home or in the church they shall always wear the cassock, which is proper to the clergy. When they go out for duty or relaxation or on a journey, they may use a shorter [coat] which is to be black in color, and which reaches to the knees, so as to distinguish it from the dress of the laity. They should reject the more elegant and worldly styles of garments, which are found today. We enjoin upon our priests as a matter of strict precept that, both at home and abroad, and whether they are residing in their own diocese or outside of it, they shall wear the Roman collar.”
— Third Plenary Council of Baltimore (1884)