Today’s reading continues directives on adult baptism:
Both the rites for the baptism of adults are to be revised: not only the simpler rite, but also the more solemn one, which must take into account the restored catechumenate. A special Mass “for the conferring of baptism” is to be inserted into the Roman Missal.
Before Vatican II, the only official baptism rite was for adults; there was not a separate ritual for children or infants. Provisional rites were drawn up in the early 70’s, and promulgated (as the “brown book”) in the US in 1974. The final version, the “white book” came into use in 1988.