Editing Introit (section)

== Use of the incipit ==
In the same way as Church documents are referred to by their [[incipit]] (their first words in Latin),<ref>Examples are the papal encyclical ''[[Humanae vitae]]'' and the Second Vatican Council's dogmatic constitution ''[[Lumen gentium]]''</ref> Mass formulas are known by the incipit of their Introit, which is the first text in the formula. Thus a Mass for the dead is referred to a ''[[Requiem]]'' Mass, and the three [[Christmas Day]] Masses have been called ''Dominus dixit'', ''Lux fulgebit'' and ''Puer natus''. So too, [[Gaudete Sunday]] is a name for the third Sunday in [[Advent]], [[Laetare Sunday]] for the fourth Sunday in [[Lent]], and [[Quasimodo Sunday]] for the [[Octave of Easter|Octave]] or Second Sunday of Easter, because of the incipit of the Entrance antiphons of those Sundays.