- Chg #3897: Raised visibility of `yii\web\View::registerAssetFiles()` to protected (samdark)
- Chg #3899: Moved `MailEvent` class to `yii\mail` namespace (cebe)
- Chg #3956: Flash messages set via `Yii::$app->session->setFlash()` will be removed only if they are accessed (qiangxue)
- Chg #3989: The default value for `yii\log\FileTarget::$rotateByCopy` now defaults to true to work on windows by default (cebe)
- Chg #4071: `mail` component renamed to `mailer`, `yii\log\EmailTarget::$mail` renamed to `yii\log\EmailTarget::$mailer` (samdark)
- Chg: Replaced `clearAll()` and `clearAllAssignments()` in `yii\rbac\ManagerInterface` with `removeAll()`, `removeAllRoles()`, `removeAllPermissions()`, `removeAllRules()` and `removeAllAssignments()` (qiangxue)
- Chg: Added `$user` as the first parameter of `yii\rbac\Rule::execute()` (qiangxue)