/**
  * Get accessor method for instance property.
  *
  * @return WP_DOM_Util Instance of the class.
  */
 public static function get_instance()
 {
     // Check if an instance has not been created yet.
     if (null == self::$instance) {
         // Set instance of class.
         self::$instance = new self();
     }
     // Return instance.
     return self::$instance;
 }