§1. In churches or oratories where it is permitted to reserve the Most Holy Eucharist, there can be expositions with the pyx or the monstrance; the norms prescribed in the liturgical books are to be observed.
§2. Exposition of the Most Blessed Sacrament is not to be held in the same area of the church or oratory during the celebration of Mass.
Source: Code of Canon Law (Vatican.va)