code/datums/elements/turf_transparency.dm

/proc/request_z_pillar	Returns a z pillar to insert turfs into
/obj/effect/abstract/z_holder	Exists to be placed on the turf of walls and such to hold the vis_contents of the tile below Otherwise the lower turf might get shifted around, which is dumb. do this instead.
/datum/z_pillar	Grouping datum that manages transparency for a block of space Setup to ease debugging, and to make add/remove operations cheaper