Catechism of the Catholic Church §1675 — excerpt
These expressions of piety extend the liturgical life of the Church, but do not replace it. They "should be so drawn up that they harmonize with the liturgical seasons, accord with the sacred liturgy, are in some way derived from it and lead the people…
This translation is under copyright, so only the cited words are quoted here. Follow the link for the full text. Translation: English translation of the Catechism of the Catholic Church, 2nd ed. (Libreria Editrice Vaticana), as posted at vatican.va.
Also cites: SC 13 # 3