public static function instance($extra_attr = array(), $id = NULL)
 {
     CrayonLog::debug('instance');
     // Create Crayon
     $crayon = new CrayonHighlighter();
     /* Load settings and merge shortcode attributes which will override any existing.
      * Stores the other shortcode attributes as settings in the crayon. */
     if (!empty($extra_attr)) {
         $crayon->settings($extra_attr);
     }
     if (!empty($id)) {
         $crayon->id($id);
     }
     return $crayon;
 }