The history of luaTEX 2006–2009 / v 0.50 - Pragma ADE

end
function filters.add(where,fnc,n)
local list = somewhere(where)
if not list then
-- error
elseif not n or n > #list + 1 then
table.insert(list,#list+1)
elseif n < 0 then
table.insert(list,1)
else
table.insert(list,n)
end
end
function filters.remove(where,fnc,n)
local list = somewhere(where)
if list and n and n > 0 and n