public function addTab($key, $label, $icon, $priority = 0, $messageCount = 0)
    {
        $this->tabs[$key] = [
            'priority'  => $priority,
            'key'       => $key,
            'label'     => $label,
            'icon'      => $icon,
            'count'     => $messageCount,
        ];
        $this->items[$key] = [];

        return $this;
    }