$bootstrap public property
List of components that should be run during the application bootstrapping process. Each component may be specified in one of the following formats: an application component ID as specified via $components. a module ID as specified via $modules. a class name. a configuration array. During the bootstrapping process, each component will be instantiated. If the component class implements yii\base\BootstrapInterface, its bootstrap() method will be also be called.
pub