message: docs: expand doc for app_initializer token
  PR Close
diff: @@ -12,7 +12,15 @@ import {Inject, Injectable, InjectionToken, Optional} from './di';
  /**
  - * A function that will be executed when an application is initialized.
  + * An injection token that allows you to provide one or more initialization functions.
  + * These function are injected at application startup and executed during
  + * app initialization. If any of these functions returns a Promise, initialization
  + * does not complete until the Promise is resolved.
  + *
  + * You can, for example, create a factory function that loads language data
  + * or an external configuration, and provide that function to the `APP_INITIALIZER` token.
  + * That way, the function is executed during the application bootstrap process,
  + * and the needed data is available on startup.
  *
  * @publicApi
  */
  