///inventoryModifyByIndex(Inventory, Pocket, Index, ValueDifference)
///Modifies a specific index; don't call this normally.
if (debug_mode)
{
    if (!instance_exists(argument0))
    {
        show_error("[Inventory] Inventory does not exist; cannot get max item count.", 0);
        return 0;
    }
}

with (argument0)
{
    if (argument2 > Max[argument1]) return 0;
    var Str = Slot[argument1, argument2];
    var Quantity = real(string_copy(Str, string_pos("|", Str) + 1, string_length(Str)));
    var Name = string_copy(Str, 1, string_pos("|", Str) - 1);

    if (Quantity + argument3 <= 0)
    {
        Slot[argument1, argument2] = "";
        return 0;
    }

    Slot[argument1, argument2] = Name + "|" + string(Quantity + argument3);
    return Quantity + argument3;
}
return 1;