Merge branch '5.4' into 6.0

* 5.4:
  Adding class constants

Author: javiereguiluz

reference/constraints/Email.rst

@@ -131,6 +131,12 @@ This option defines the pattern used to validate the email address. Valid values
 * ``strict`` uses the `egulias/email-validator`_ library (which you must
   install separately) for validation according to `RFC 5322`_.
 
+.. tip::
+
+    The possible values of this option are also defined as PHP constants of
+    :class:`Symfony\\Component\\Validator\\Constraints\\Email`
+    (e.g. ``Email::VALIDATION_MODE_STRICT``).
+
 The default value used by this option is set in the
 :ref:`framework.validation.email_validation_mode <reference-validation-email_validation_mode>`
 configuration option.