Merge branch '2.3' into 2.5

* 2.3:
  [#4276] Making language correction we agreed on
  [Cookbook][External Parameters] Enhance description of environment variables
  Make a small grammatical adjustment

Author: weaverryan

components/http_foundation/session_configuration.rst

@@ -181,7 +181,7 @@ which runs reasonably frequently. The ``cookie_lifetime`` would be set to a
 relatively high value, and the garbage collection ``gc_maxlifetime`` would be set
 to destroy sessions at whatever the desired idle period is.
 
-The other option is to specifically checking if a session has expired after the
+The other option is specifically check if a session has expired after the
 session is started. The session can be destroyed as required. This method of
 processing can allow the expiry of sessions to be integrated into the user
 experience, for example, by displaying a message.

cookbook/configuration/external_parameters.rst

@@ -14,9 +14,13 @@ Environment Variables
 ---------------------
 
 Symfony will grab any environment variable prefixed with ``SYMFONY__`` and
-set it as a parameter in the service container. Double underscores are replaced
-with a period, as a period is not a valid character in an environment variable
-name.
+set it as a parameter in the service container. Some transformations are 
+applied to the resulting parameter name:
+
+* ``SYMFONY__`` prefix is removed;
+* Parameter name is lowercased;
+* Double underscores are replaced with a period, as a period is not 
+  a valid character in an environment variable name.
 
 For example, if you're using Apache, environment variables can be set using
 the following ``VirtualHost`` configuration:
@@ -94,6 +98,14 @@ You can now reference these parameters wherever you need them.
             )
         ));
 
+.. note::
+
+    Even in debug mode, setting or changing an environment variable
+    requires your cache to be cleared to make the parameter available.
+    In debug mode, this is required since only a change to a configuration
+    file that is loaded by Symfony triggers your configuration to be
+    re-evaluated.
+
 Constants
 ---------