- Chg #4051: Renamed `yii\caching\GroupDependency` to `TagDependency` and added support for associating multiple tags to a single cached data item (qiangxue)
- Chg #4071: `mail` component renamed to `mailer`, `yii\log\EmailTarget::$mail` renamed to `yii\log\EmailTarget::$mailer` (samdark)
- Chg #4147: `BaseMailer::compose()` will not overwrite the `message` parameter if it is explicitly provided (qiangxue)
- Chg #4188: API exceptions are now exposing less data when YII_DEBUG is false (samdark)
- Chg #4201: change default value of `SyslogTarget::facility` from LOG_SYSLOG to LOG_USER (dizews)
- Chg #4211: BaseActiveRecord::populateRecord now silently hide selected columns that are not defined in AR instead of failing with an error (miramir)
- Chg #4227: `\yii\widgets\LinkPager::$hideOnSinglePage` is now `true` by default (samdark)