public static function copyright($atts = array())
 {
     $defaults = array();
     $defaults['owner'] = Footer_Credits_Options::get_term('owner');
     $defaults['copyright_start_year'] = Footer_Credits_Options::get_term('copyright_start_year');
     $defaults['footer_class'] = self::CODE;
     $params = shortcode_atts($defaults, $atts);
     //apply plugin defaults
     return sprintf('<span class="%1$s">%2$s</span>', $params['footer_class'], self::copyright_owner($params));
 }