Total reword

Author: javiereguiluz

reference/constraints/Timezone.rst

@@ -23,7 +23,7 @@ Basic Usage
 -----------
 
 Suppose you have a ``UserSettings`` class, with a ``timezone`` field that is a
-string meant to contain a `PHP timezone identifier`_ (e.g. ``America/New_York``):
+string which contains any of the `PHP timezone identifiers`_ (e.g. ``America/New_York``):
 
 .. configuration-block::
 
@@ -103,10 +103,15 @@ The value of this option must be a valid `ISO 3166-1 alpha-2`_ country code
 intlCompatible
 ~~~~~~~~~~~~~~
 
-**type**: ``boolean`` **default**: ``false``
+**type**: ``boolean`` **default**: depends on your application
 
-If ``true``, this constraint also considers valid any of the
-:ref:`ICU timezones <component-inlt-timezones>` provided by the Intl component.
+If ``false``, only the `PHP timezone identifiers`_ are considered valid. If
+``true``, the :ref:`ICU timezones <component-inlt-timezones>` provided by the
+Intl component are considered valid too.
+
+The default value of this option depends on your application. If the
+:doc:`Intl component </components/intl>` is available in the application, the
+default value is ``true``; otherwise, it's ``false`` by default.
 
 message
 ~~~~~~~
@@ -152,6 +157,6 @@ In addition, there are some special zone values:
 * ``\DateTimeZone::PER_COUNTRY`` restricts the valid timezones to a certain
   country (which is defined using the ``countryCode`` option).
 
-.. _`PHP timezone identifier`: https://www.php.net/manual/en/timezones.php
+.. _`PHP timezone identifiers`: https://www.php.net/manual/en/timezones.php
 .. _`DateTimeZone`: https://www.php.net/datetimezone
 .. _`ISO 3166-1 alpha-2`: https://en.wikipedia.org/wiki/ISO_3166-1_alpha-2