- Deprecated `yii\base\BaseObject::className()` in favor of native PHP syntax `::class`, which does not trigger autoloading
- Deprecated XCache and Zend data cache support as caching backends
- Deprecated `yii\BaseYii::powered()` method
- Added `yii\base\InvalidArgumentException` and deprecated `yii\base\InvalidParamException`
- Added `yii\BaseYii::debug()` and deprecated `yii\BaseYii::trace()`
- Bug #13350: Fixed bug with incorrect caching of `yii\web\UrlRule::createUrl()` results in `yii\web\UrlManager`.
- Bug #14094: Fixed bug when single `yii\web\UrlManager::createUrl()` call my result multiple calls of `yii\web\UrlRule::createUrl()` for the same rule.
- Enh #11288: Added support for caching of `yii\web\UrlRule::createUrl()` results in `yii\web\UrlManager` for rules with defaults.