As we mentioned already, Domain Events talk about the past and describe changes in your Domain that have already occurred. By definition, it's impossible to change the past, unless you're Marty McFly and have a DeLorean, which is probably not the case. So just remember that Domain Events are immutable.
Symfony Event Dispatcher
Some PHP frameworks support Events. However, don't confuse those Events with Domain Events; they're different in characteristics and goals. For example, Symfony has the Event Dispatcher component, and if you need to implement an Event system for a state machine, you can rely on it. In Symfony, the transformation from requests to responses is handled by Events too. However, Symfony Events are mutable, and each of the listeners is capable of modifying, adding to, or updating the information in the Event.
Some PHP frameworks support Events. However, don't confuse those Events with Domain Events; they're different in characteristics and goals. For example, Symfony has the Event Dispatcher component, and if you need to implement an Event system for a state machine, you can rely on it. In Symfony, the transformation from requests to responses is handled by Events too. However, Symfony Events are mutable, and each of the listeners is capable of modifying, adding to, or updating the information in the Event.