/**
  * @param XCube_PropertyInterface $property
  * @param array $vars
  * @return bool
  */
 public function isValid(XCube_PropertyInterface $property, $vars)
 {
     if ($property->isNull()) {
         return true;
     }
     $value = $property->get();
     if (preg_match('/^[0-9]+$/', $value)) {
         return true;
     }
     return false;
 }