- Chg: `yii\web\Request::cookieValidationKey` must be explicitly specified for each application that wants to use cookie validation (qiangxue)
- New #3911: Added `yii\behaviors\SluggableBehavior` that fills the specified model attribute with the transliterated and adjusted version to use in URLs (creocoder)
- New #4193: Added `yii\filters\Cors` CORS filter to allow Cross Origin Resource Sharing (pgaultier)