How do event priorities work in Symfony?

The Symfony event system uses integers to indicate the priority of an event listener where the higher the number, the earlier the event listener is executed.

The priorities of the internal Symfony event listeners usually range from -256 to 256. When adding your custom event listeners, you can define an integer to control when your event listener should run in relation to either Symfony’s internal event listeners or your other custom event listeners.

Sources & further readings

• Events and Event Listeners – Symfony docs