The NEC-2 input format is based on "cards" (e.g. CE, GW, GE, FR, EX, RP, EN).
The authoritative reference for these cards is the NEC-2 Part 3 (Program Description)
manual:
https://www.nec2.org/other/nec2prt3.pdf
Consult it when you need the field layout, parameters, or semantics of a specific card.