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;