It is done, secundum usum Sarum.

This proverb, says Fuller, coming out of the church, has since enlarged itself into civil use. It begun on this occasion: many offices, or forms of service, were used in several churches in England; as the office of York, Hereford, Bangor, &c. which caused a deal of confusion in God’s worship; until Osmond, Bishop of Sarum, about the year of our Lord 1090, made that ordinal, or office, which was generally received all over England; so that churches, henceforward, easily understood one another, all speaking the same words in their liturgy.

It is now applied to those persons who do, and actions which are formally and solemnly done, in so regular a way, by authentic precedents, and patterns of unquestionable authority, that no just exceptions can be taken thereat.