The Tabernacle in pre-1983 Canon Law

From the 1917 Pio-Benedictine Code of Canon Law
(the canon law in effect when Eucharisticum Mysterium was published):

Canon 1268

§1. The most holy Eucharist cannot be kept continually, that is, habitually, except on only one altar of the church.

§2. It shall be kept in the most excellent and the most noble place of the church and therefore regularly on the major altar unless it seems that the veneration and cult of such a sacrament is more convenient and decent elsewhere, observing the prescriptions of liturgical law, which pertain to the final days of the great week.

§3. But in cathedral churches or in collegial or conventual ones in which choral functions are conducted at the main altar, lest ecclesiastical officials be impeded, it is opportune that the most holy Eucharist not regularly be kept at the major altar but in another chapel or altar.

§4. Let rectors of churches take care that the altar in which the most holy Sacrament is reserved be decorated above all the others so that by this appearance the faithful be moved to greater piety and devotion.

Canon 1269

§ 1 The most Holy Eucharist must be preserved in an immovable tabernacle located in the center part of the altar.

§ 2 The tabernacle shall be well-constructed, closed on all sites, decently decorated according to the norm of liturgical law, empty of all foreign things, and thus carefully kept so that any sort of danger of sacrilege or profanation is excluded.

§ 3 If grave causes, approved by the local Ordinary, so persuade, it is not forbidden to preserve the most Holy Eucharist at nighttime outside the altar but on a corporal in a safe and decent place with due regard for the prescription of Canon 1271.

§ 4 The key of the tabernacle in which the most Holy Sacrament is preserved must be diligently kept, gravely burdening the conscience of the priest who has care of the church or oratory.