public function add($label, $content = null, $tabId = null, $active = false)
    {
        $tabId = is_null($tabId) ? $this->getTabId() : $tabId;
        $label = is_null($label) ? $tabId : $label;

        $this->tabs[$tabId] = array (
            'label'     => $label,
            'content'   => $content,
            'active'    => $active,
        );

        return $this;
    }