Represents an event cause by user's openning or closing something at the client.
Note: it is a bit confusing but
Events.ON_CLOSE is sent when user clicks a close button. It is a request to ask the server to close a window, a tab or others. If the server ignores the event, nothing will happen at the client. By default, the component is detached when receiving this event.
On the other hand,
OpenEvent) is a notification. It is sent to notify the server that the client has opened or closed something. And, the server can not prevent the client from opening or closing.