Merge branch '6.0' into 6.1

* 6.0:
  Correct time type return
  Fix a typo
  Reword
  add tip about listener priority to mailer.rst

Author: javiereguiluz

components/phpunit_bridge.rst

@@ -540,7 +540,7 @@ is mocked so it uses the mocked time if no timestamp is specified.
 Other functions with an optional timestamp parameter that defaults to ``time()``
 will still use the system time instead of the mocked time. This means that you
 may need to change some code in your tests. For example, instead of ``new DateTime()``,
-you should use ``DateTime::createFromFormat('U', time())`` to use the mocked
+you should use ``DateTime::createFromFormat('U', (string) time())`` to use the mocked
 ``time()`` function.
 
 To use the ``ClockMock`` class in your test, add the ``@group time-sensitive``

mailer.rst

@@ -936,6 +936,8 @@ This makes use of the :ref:`styles Twig namespace <mailer-css-namespace>` we cre
 earlier. You could, for example, `download the foundation-emails.css file`_
 directly from GitHub and save it in ``assets/styles``.
 
+.. _signing-and-encrypting-messages:
+
 Signing and Encrypting Messages
 -------------------------------
 
@@ -1389,6 +1391,13 @@ is sent::
         }
     }
 
+.. tip::
+
+    When using a ``MessageEvent`` listener to
+    :doc:`sign the email contents <signing-and-encrypting-messages>`, run it as
+    late as possible (e.g. setting a negative priority for it) so the email
+    contents are not set or modified after signing them.
+
 Development & Debugging
 -----------------------