In the Roman Catholic Church, except for the altogether distinct Ambrosian rite (see Ambrose, Saint) and for some variant forms among religious orders, especially that of the Dominicans, the service is the same everywhere, under regulation of the Holy See. The language of the liturgy is typically terse. The celebrant, who must be a priest, follows a prescribed missal and wears certain vestments. Mass is said at an altar containing relics; two candles must be burning. A congregation is not essential, but solitary Mass is discouraged. A High (solemn) Mass requires a priest, deacon, and choir. Low Mass, much more common, is the same service said by one priest. Normally at Low Mass a server or acolyte, traditionally called an altar boy but now often a girl, helps the celebrant. Most of the text is invariable, or "ordinary," but certain parts, called "proper," change with the occasion or day. Mass may be offered with a special intention, as in thanksgiving or for peace. A requiem is a proper Mass for the dead. Most priests say Mass daily. Sunday Mass is an important sociocultural factor in Roman Catholic life. All members are required to attend Mass on Sunday as a minimum participation in public worship.