Yii event is the first framework-specific package from Yii 3 family. Its goal is to make configuring events convenient. For the applications it provides three main config files:

• events.php - Common event handlers for web and console.
• events-web.php - Web event handlers.
• events-console.php - Console event handlers.

The config syntax is the following:

return [
    EventName::class => [
        // Just a regular closure, it will be called from the Dispatcher "as is".
        static fn (EventName $event) => someStuff($event),
        
        // A regular closure with additional dependency. All the parameters after the first one (the event itself)
        // will be resolved from your DI container within `yiisoft/injector`.
        static fn (EventName $event, DependencyClass $dependency) => someStuff($event),
        
        // An example with a regular callable. If the `staticMethodName` method contains some dependencies,
        // they will be resolved the same way as in the previous example.
        [SomeClass::class, 'staticMethodName'],
        
        // Non-static methods are allowed too. In this case `SomeClass` will be instantiated by your DI container.
        [SomeClass::class, 'methodName'],
        
        // An object of a class with the `__invoke` method implemented
        new InvokableClass(),
        
        // In this case the `InvokableClass` with the `__invoke` method will be instantiated by your DI container
        InvokableClass::class,
        
        // Any definition of an invokable class may be here while your `$container->has('the definition)` 
        'di-alias'
    ],
];

For convenience, there's a configuration checker that is used in current application templates to check if all handlers declared are correct.