/**
  * warning constructor.
  *
  * @param  $msg - warning message
  * @param  $code - warning code
  */
 public function __construct($msg, $code = AC_ERR_USER_WARNING)
 {
     parent::__construct($msg, $code);
     $backtrace = debug_backtrace();
     $this->msg = $msg . ' in ' . $backtrace[0]['file'] . ' on line ' . $backtrace[0]['line'];
 }