/**
  * Return attributes to shortcode string.
  * 
  * @since 1.0.0
  * @access public
  * @param array $atts 
  * @param string $content 
  * @return string
  */
 public static function to_shortcode($sc_name, $atts, $content = null, $enclosed = true)
 {
     $shortcode = sprintf('[%s', $sc_name);
     $shortcode .= count($atts) > 0 ? TF_Model::parse_attr($atts) : '';
     $shortcode .= ']';
     $shortcode .= $enclosed ? $content . sprintf('[/%s]', $sc_name) : '';
     return $shortcode;
 }