Symfony follows this logic to decide which method to execute inside the event

listener class:

#. If the ``kernel.event_listener`` tag defines the ``method`` attribute, that's

the name of the method to be executed;

#. If no ``method`` attribute is defined, try to execute the method whose name

is ``on`` + "camel-cased event name" (e.g. ``onKernelException()`` method for

the ``kernel.exception`` event);

#. If that method is not defined either, try to execute the ``__invoke()`` magic

method (which makes event listeners invokable);

#. If the ``_invoke()`` method is not defined either, throw an exception.

..versionadded::4.1

The support of the ``__invoke()`` method to create invokable event listeners

was introduced in Symfony 4.1.

..note::

There is an optional tag attribute called ``method`` which defines which method

to execute when the event is triggered. By default the name of the method is

``on`` + "camel-cased event name". If the event is ``kernel.exception`` the

method executed by default is ``onKernelException()``.

The other optional tag attribute is called ``priority``, which defaults to

``0`` and it controls the order in which listeners are executed (the highest

the priority, the earlier a listener is executed). This is useful when you

need to guarantee that one listener is executed before another. The priorities

of the internal Symfony listeners usually range from ``-255`` to ``255`` but

your own listeners can use any positive or negative integer.

There is an optional attribute for the ``kernel.event_listener`` tag called

``priority``, which defaults to ``0`` and it controls the order in which

listeners are executed (the highest the priority, the earlier a listener is

executed). This is useful when you need to guarantee that one listener is

executed before another. The priorities of the internal Symfony listeners

usually range from ``-255`` to ``255`` but your own listeners can use any

positive or negative integer.

.. _events-subscriber: