export_descr_unit.txt

[The_Mark]

; category (infantry, cavalry, siege, handler, ship or non_combatant)
; class (light, heavy, missile or spearmen)
; Category and class define the basic unit type. They're used for setting some default attributes,
; and for determining where units are placed in a formation, amongst other things.

There is actually one more valid unit class, skirmish. It is unused in EDU but it is used in descr_formations_ai and all needed text strings exist. Dunno why it wasn't used.