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Tweak the explanation about event priorities #12795

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Dec 11, 2019
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Tweak the explanation about event priorities #12795

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20 changes: 11 additions & 9 deletions event_dispatcher.rst
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Expand Up @@ -115,11 +115,11 @@ using a special "tag":
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 higher
the number 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.
``0`` and it controls the order in which listeners are executed for a given
event (the higher the number 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:

Expand All @@ -131,10 +131,12 @@ that defines one or more methods that listen to one or various events. The main
difference with the event listeners is that subscribers always know which events
they are listening to.

In a given subscriber, different methods can listen to the same event. The order
in which methods are executed is defined by the ``priority`` parameter of each
method (the higher the number the earlier the method is called). To learn more
about event subscribers, read :doc:`/components/event_dispatcher`.
If different event subscriber methods listen to the same event, their order is
defined by the ``priority`` parameter. This value is a positive or negative
integer which defaults to ``0``. The higher the number, the earlier the method
is called. **Priority is aggregated for all listeners and subscribers**, so your
methods could be executed before or after the methods defined in other listeners
and subscribers. To learn more about event subscribers, read :doc:`/components/event_dispatcher`.

The following example shows an event subscriber that defines several methods which
listen to the same ``kernel.exception`` event::
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