Merge branch '3.4' into 4.0

* 3.4:
  Update dependency_injection.rst
  Update dependency_injection.rst
  Fix some misspellings
  Explained how the URL trailing slash redirection works

Author: javiereguiluz

components/validator.rst

@@ -23,7 +23,7 @@ Usage
 
 The Validator component behavior is based on two concepts:
 
-* Contraints, which define the rules to be validated;
+* Constraints, which define the rules to be validated;
 * Validators, which are the classes that contain the actual validation logic.
 
 The following example shows how to validate that a string is at least 10

create_framework/dependency_injection.rst

@@ -10,9 +10,10 @@ to it::
     namespace Simplex;
 
     use Symfony\Component\EventDispatcher\EventDispatcher;
-    use Symfony\Component\Routing;
     use Symfony\Component\HttpFoundation;
+    use Symfony\Component\HttpFoundation\RequestStack;
     use Symfony\Component\HttpKernel;
+    use Symfony\Component\Routing;
 
     class Framework extends HttpKernel\HttpKernel
     {
@@ -195,7 +196,7 @@ Now, here is how you can register a custom listener in the front controller::
     // ...
     use Simplex\StringResponseListener;
 
-    $container->register('listener.string_response', StringResposeListener::class);
+    $container->register('listener.string_response', StringResponseListener::class);
     $container->getDefinition('dispatcher')
         ->addMethodCall('addSubscriber', array(new Reference('listener.string_response')))
     ;

http_cache.rst

@@ -301,7 +301,7 @@ two things:
   (e.g. deleting a blog post). Caching them would prevent certain requests from hitting
   and mutating your application.
 
-* POST requests are generally considered uncachable, but `they can be cached`_
+* POST requests are generally considered uncacheable, but `they can be cached`_
   when they include explicit freshness information. However POST caching is not
   widely implemented, so you should avoid it if possible.
 

routing.rst

@@ -493,6 +493,30 @@ that are special: each adds a unique piece of functionality inside your applicat
 ``_locale``
     Used to set the locale on the request (:ref:`read more <translation-locale-url>`).
 
+Redirecting URLs with Trailing Slashes
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Historically, URLs have followed the UNIX convention of adding trailing slashes
+for directories (e.g. ``https://example.com/foo/``) and removing them to refer
+to files (``https://example.com/foo``). Although serving different contents for
+both URLs is OK, nowadays it's common to treat both URLs as the same URL and
+redirect between them.
+
+Symfony follows this logic to redirect between URLs with and without trailing
+slashes (but only for ``GET`` and ``HEAD`` requests):
+
+----------  ----------------------------------------  ------------------------------------------
+Route path  If the requested URL is ``/foo``          If the requested URL is ``/foo/``
+----------  ----------------------------------------  ------------------------------------------
+``/foo``    It matches (``200`` status response)      It doesn't match (``404`` status response)
+``/foo/``   It makes a ``301`` redirect to ``/foo/``  It matches (``200`` status response)
+----------  ----------------------------------------  ------------------------------------------
+
+In summary, adding a trailing slash in the route path is the best way to ensure
+that both URLs work. Read the :doc:`/routing/redirect_trailing_slash` article to
+learn how to avoid the ``404`` error when the request URL contains a trailing
+slash and the route path does not.
+
 .. index::
    single: Routing; Controllers
    single: Controller; String naming format