public static function tab($atts, $content = null)
 {
     extract(shortcode_atts(array('title' => ''), $atts));
     self::$tabsCounters = self::$tabsCounters > 0 ? (int) self::$tabsCounters : 0;
     self::$tabsCounters++;
     self::$tabsTitles[self::$tabsCounters] = $title;
     $output = '<div class="tab-pane' . (self::$tabsActive === true ? ' active' : '') . '" id="tab' . self::$tabsCounters . '"><p>' . do_shortcode($content) . '</p></div>';
     self::$tabsActive = false;
     return $output;
 }