This folder contains official Yii 2 extensions. To add a new extension named `xyz` (must be in lower case), take the following steps: 1. create a folder named `xyz` under `yii` and put all relevant source code there; 2. create the following accessory files (please refer to any existing extension): * `composer.json` * `README.md` * `CHANGELOG.md` * `LICENSE.md` 3. ask Qiang to create a subsplit for `xyz` and a composer package named `yii2-xyz`; 4. modify `/composer.json` and add `xyz` to the `replace` section; 5. modify `/build/controllers/PhpDocController.php` about the method `actionProperty()`.