/**
* Xapp_Singleton interface impl.
*
* static singleton method to create static instance of driver with optional third parameter
* xapp options array or object
*
* @error 15501
* @param null|mixed $options expects optional xapp option array or object
* @return XApp_Commander_Bootstrap
*/
public static function instance($options = null)
{
if (self::$_instance === null) {
self::$_instance = new self($options);
}
return self::$_instance;
}