ISBD:

Code i (Leader/18) indicates at a minimum the use of ISBD practices in records. This category includes:

records done according to AACR 1 revised chapter 6, Separately Published Monographs

records exemplifying ISBD punctuation practices applied to pre-AACR 2 records

new records that are basically formulated according to AACR 2 but contain heading forms not used under those rules

records that use ISBD punctuation but whose other conventions are unknown