The framework supports client-side and server-side controllers. An event is always wired
to a client-side controller action, which can in turn call a server-side controller action.
For example, a client-side controller might handle an event and call a server-side
controller action to persist a record.
Server-side actions need to make a round trip, from the client to the server and back again, so
they usually complete more slowly than client-side actions.
For more details on the process of calling a server-side action,
see Calling a Server-Side Action.