public function registerModule($module, $overload = false)
    {
        if (is_string($module)) {
            // attempt to load the module
            $original_module = $module;
            $ok = false;
            foreach ($this->prefixes as $prefix) {
                $module = $prefix . $original_module;
                if (class_exists($module)) {
                    $ok = true;
                    break;
                }
            }
            if (!$ok) {
                $module = $original_module;
                if (!class_exists($module)) {
                    trigger_error(
                        $original_module . ' module does not exist',
                        E_USER_ERROR
                    );
                    return;
                }
            }
            $module = new $module();
        }
        if (empty($module->name)) {
            trigger_error('Module instance of ' . get_class($module) . ' must have name');
            return;
        }
        if (!$overload && isset($this->registeredModules[$module->name])) {
            trigger_error('Overloading ' . $module->name . ' without explicit overload parameter', E_USER_WARNING);
        }
        $this->registeredModules[$module->name] = $module;
    }