public static function accordion($atts, $content = null)
{
extract(shortcode_atts(array('title' => '', 'opened' => 'no'), $atts));
self::$accordionCounters = self::$accordionCounters > 0 ? (int) self::$accordionCounters : 0;
self::$accordionCounters++;
return '
<div class="panel panel-default">
<div class="panel-heading"><h5 class="panel-title"><a href="#collapse' . self::$accordionCounters . '" data-toggle="collapse" data-parent="#accordion' . self::$accordionsCounters . '">' . esc_html($title) . '</a></h5></div>
<div id="collapse' . self::$accordionCounters . '" class="panel-collapse collapse' . ($opened == 'yes' ? ' in' : '') . '"><div class="panel-body"><p>' . do_shortcode($content) . '</p></div></div></div>';
}
