public function __construct($node, $parent)
{
parent::__construct($node, $parent);
self::$possible_attributes = array_merge(parent::$possible_attributes, self::$possible_attributes);
self::$required_attributes = array_merge(parent::$required_attributes, self::$required_attributes);
self::$possible_children = array_merge(parent::$possible_children, self::$possible_children);
self::$required_children = array_merge(parent::$required_children, self::$required_children);
}