29 Servers, lectors commentators, and members of the choir also exercise a genuine liturgical function. They ought, therefore, to discharge their office with the sincere piety and decorum demanded by so exalted a ministry and rightly expected of them by God's people. Consequently they must all be deeply imbued with the spirit of the liturgy, each in his own measure, and they must be trained to perform their functions in a correct and orderly manner.
Source: Sacrosanctum Concilium (Vatican.va)