if doc.sub.items then
	local register_factoid = doc.sub.items.register_factoid
	local function group_factoid(cat, gr, f)
		register_factoid(cat, "groups", function(_, def)
			return f(def.groups[gr] or 0) or ""
		end)
	end
	for cat, cinfo in pairs{
		nodes = {
			advtrains_signal = function(x)
				if x == 1 then
					return "This is a signal with a static aspect."
				elseif x == 2 then
					return "This is a signal with an adjustable aspect."
				end
			end,
			not_blocking_trains = "This block does not block trains.",
			save_in_at_nodedb = "This block is saved in the Advtrains node database.",
		},
		craftitems = {
			at_control = "This wagon has at least one driver stand.",
			at_freight = "This wagon can hold freight.",
			at_loco = "This wagon is a locomotive.",
			at_pax = "This wagon has at least one seat for passengers.",
		}
	} do
		for group, ginfo in pairs(cinfo) do
			local tp = type(ginfo)
			if tp == "string" then
				group_factoid(cat, group, function(x)
					if x > 0 then
						return ginfo
					end
				end)
			elseif tp == "function" then
				group_factoid(cat, group, ginfo)
			end
		end
	end
end