document the 2.5 validation options

reference/configuration/framework.rst

@@ -48,6 +48,12 @@ Configuration
 * `translator`_
     * :ref:`enabled <translator.enabled>`
     * `fallback`_
+* `validation`_
+    * `cache`_
+    * `enable_annotations`_
+    * `translation_domain`_
+    * `strict_email`_
+    * `api`_
 
 secret
 ~~~~~~
@@ -517,6 +523,70 @@ This option is used when the translation key for the current locale wasn't found
 
 For more details, see :doc:`/book/translation`.
 
+validation
+~~~~~~~~~~
+
+cache
+.....
+
+**type**: ``string``
+
+This value is used to determine the service that is used to persist class
+metadata in a cache. The actual service name is built by prefixing the configured
+value with ``validator.mapping.cache.`` (e.g. if the value is ``apc``, the
+``validator.mapping.cache.apc`` service will be injected). The service has
+to implement the :class:`Symfony\\Component\\Validator\\Mapping\\Cache\\CacheInterface`.
+
+enable_annotations
+..................
+
+**type**: ``Boolean`` **default**: ``false``
+
+If this option is enabled, validation constraints can be defined using annotations.
+
+translation_domain
+..................
+
+**type**: ``string`` **default**: ``validators``
+
+The translation domain that is used when translating validation constraint
+error messages.
+
+strict_email
+............
+
+.. versionadded:: 2.5
+    The ``strict_email`` option was introduced in Symfony 2.5.
+
+**type**: ``Boolean`` **default**: ``false``
+
+If this option is enabled, the `egulias/email-validator`_ library will be
+used by the :doc:`/reference/constraints/Email` constraint validator. Otherwise,
+the validator uses a simple regular expression to validate email addresses.
+
+api
+...
+
+.. versionadded:: 2.5
+    The ``api`` option was introduced in Symfony 2.5.
+
+**type**: ``string``
+
+Starting with Symfony 2.5, the Validator component introduced a new validation
+API. The ``api`` option is used to switch between the different implementations:
+
+``2.4``
+    Use the vaidation API that is compatible with older Symfony versions.
+
+``2.5``
+    Use the validation API introduced in Symfony 2.5.
+
+``2.5-bc`` or ``auto``
+    If you omit a value or set the ``api`` option to ``2.5-bc`` or ``auto``,
+    Symfony will use an API implementation that is compatible with both the
+    legacy implementation and the ``2.5`` implementation. You have to use
+    PHP 5.3.9 or higher to be able to use this implementation.
+
 Full default Configuration
 --------------------------
 
@@ -646,3 +716,4 @@ Full default Configuration
 
 .. _`protocol-relative`: http://tools.ietf.org/html/rfc3986#section-4.2
 .. _`PhpStormOpener`: https://github.com/pinepain/PhpStormOpener
+.. _`egulias/email-validator`: https://github.com/egulias/EmailValidator