Merge branch '4.4' into 5.4

* 4.4:
  add command related to tags
  added validation model ref link

Author: javiereguiluz

http_cache/validation.rst

@@ -9,7 +9,7 @@ data, the expiration model falls short. With the `expiration model`_, the
 application won't be asked to return the updated response until the cache
 finally becomes stale.
 
-The validation model addresses this issue. Under this model, the cache continues
+The `validation model`_ addresses this issue. Under this model, the cache continues
 to store responses. The difference is that, for each request, the cache asks the
 application if the cached response is still valid or if it needs to be regenerated.
 If the cache *is* still valid, your application should return a 304 status code
@@ -235,6 +235,7 @@ headers that must not be present for ``304`` responses (see
 :method:`Symfony\\Component\\HttpFoundation\\Response::setNotModified`).
 
 .. _`expiration model`: https://tools.ietf.org/html/rfc2616#section-13.2
+.. _`validation model`: https://tools.ietf.org/html/rfc2616#section-13.3
 .. _`HTTP ETag`: https://en.wikipedia.org/wiki/HTTP_ETag
 .. _`DeflateAlterETag`: https://httpd.apache.org/docs/trunk/mod/mod_deflate.html#deflatealteretag
 .. _`BrotliAlterETag`: https://httpd.apache.org/docs/2.4/mod/mod_brotli.html#brotlialteretag

reference/dic_tags.rst

@@ -8,6 +8,18 @@ services that require special processing, like console commands or Twig extensio
 This article shows the most common tags provided by Symfony components, but in
 your application there could be more tags available provided by third-party bundles.
 
+Run this command to display tagged services in your application:
+
+.. code-block:: terminal
+
+    $ php bin/console debug:container --tags
+
+To search for a specific tag, re-run this command with a search term:
+
+.. code-block:: terminal
+
+    $ php bin/console debug:container --tag=form.type
+
 assets.package
 --------------