Directory on Popular Piety and the Liturgy (DPPL). First special term with which we familiarize ourselves: Pious Exercise. What on earth …?

7. The expression “pious exercise” in this Directory refers to those public or private expressions of Christian piety which, although not part of the Liturgy, are considered to be in harmony with the spirit, norms, and rhythms of the Liturgy. Moreover, such pious exercises are inspired to some degree by the Liturgy and lead the Christian people to the Liturgy (Cf. SC 13). Some pious exercises have been established by mandate of the Apostolic See or by mandate of the Bishops (Cf. SC 13). Many of these exercises are part of the cultic patrimony of particular Churches or religious families. Pious exercises always refer to public divine revelation and to an ecclesial background. They often refer to the grace revealed by God in Jesus Christ and, in conformity with the laws of the Church, they are practised “in accordance with approved customs or books” (SC 13).

Vatican II constructs the essence of this section. The liturgy, especially the Mass, is the desired end for devotional activity.

Not also the comment above on public divine revelation. Things like secrets, gnostic little bits that may have crept into piety, these are not part of the tradition that aims people to God and to the Mass. The emphasis that concludes this section is typical of the retrenchment of the later years of the John Pau II papacy: just making sure lay stuff stays within the bounds of approval.