public function setGetAllHtmlPrefix($referrerType)
    {
        // get singular label for referrer type
        $indexTranslation = '';
        switch ($referrerType) {
            case Common::REFERRER_TYPE_DIRECT_ENTRY:
                $indexTranslation = 'Referrers_DirectEntry';
                break;
            case Common::REFERRER_TYPE_SEARCH_ENGINE:
                $indexTranslation = 'General_ColumnKeyword';
                break;
            case Common::REFERRER_TYPE_SOCIAL_NETWORK:
                $indexTranslation = 'Referrers_ColumnSocial';
                break;
            case Common::REFERRER_TYPE_WEBSITE:
                $indexTranslation = 'Referrers_ColumnWebsite';
                break;
            case Common::REFERRER_TYPE_CAMPAIGN:
                $indexTranslation = 'Referrers_ColumnCampaign';
                break;
            default:
                // case of newsletter, partners, before Piwik 0.2.25
                $indexTranslation = 'General_Others';
                break;
        }

        $label = strtolower(Piwik::translate($indexTranslation));

        // return html that displays it as grey & italic
        return '<span class="datatable-label-category">(' . $label . ')</span>';
    }