- Enh #4080: Added proper handling and support of the symlinked directories in `FileHelper`, added $options parameter in `FileHelper::removeDirectory()` (resurtm)
- Enh #4086: changedAttributes of afterSave Event now contain old values (dizews)
- Enh #4114: Added Security::generateRandomHexKey(), used it for various tokens and default key generation (samdark)
- Enh: Added support for using sub-queries when building a DB query with `IN` condition (qiangxue)
- Enh: Supported adding a new response formatter without the need to reconfigure existing formatters (qiangxue)
- Enh: Added `yii\web\UrlManager::addRules()` to simplify adding new URL rules (qiangxue)