Note: No S, T, U, V, W, X; skip Y & Z
Grey = No Top-Level '0' Category (A & O)
Legend:
Yes = Exactly As Is
See Below = Specific L3 Beneath But Not This L2 Generally
General = Only Top Level L3 (equivalent to its L2)
Source: https://www.aeaweb.org/jel/guide/jel.php