vocabularies

Which egg-holding form an egg tray is — an open tray (an uncovered filler-flat of moulded cells, stackable, the 30-egg trade tray) or a lidded box (a hinged or lidded carton enclosing its cells for carrying and protection, the 10- or 12-egg household egg box). These forms share the EggTray slot-profile (moulded per-egg cells counted by egg_capacity) and differ only by this enclosure plus capacity, colour and material — so they are VALUES here, not classes.

Answers the question: egg tray type.