A kind of Utkālika Śruta (a category of Āgamas (canonical works), which is allowed to be studied at all time barring the akāla prahara (i.e., the period in which the study of Āgamas is prohibited)),
which contains the description of kalpa (that which is permitted) and akalpa (that which is forbideen).
kappamakappaṃ ca jattha sute vaṇṇijjati taṃ kappiyākappiyam.
(Nandí 77 Cū p. 57)