Documented the default values of Accept headers

components/http_foundation.rst

@@ -269,6 +269,19 @@ If you need to get full access to parsed data from ``Accept``, ``Accept-Language
     $accepts = AcceptHeader::fromString($request->headers->get('Accept'))
         ->all();
 
+The default values that can be optionally included in the ``Accept-*`` headers
+are also supported::
+
+    $acceptHeader = 'text/plain;q=0.5, text/html, text/*;q=0.8, */*;q=0.3';
+    $accept = AcceptHeader::fromString($acceptHeader);
+
+    $quality = $accept->get('text/xml')->getQuality(); // $quality = 0.8
+    $quality = $accept->get('application/xml')->getQuality(); // $quality = 0.3
+
+.. versionadded:: 4.1
+    The support of default values in the ``Accept-*`` headers was introduced in
+    Symfony 4.1.
+
 Accessing other Data
 ~~~~~~~~~~~~~~~~~~~~
 
@@ -403,7 +416,7 @@ of methods to manipulate the HTTP headers related to the cache:
 .. note::
 
     The methods :method:`Symfony\\Component\\HttpFoundation\\Response::setExpires`,
-    :method:`Symfony\\Component\\HttpFoundation\\Response::setLastModified` and 
+    :method:`Symfony\\Component\\HttpFoundation\\Response::setLastModified` and
     :method:`Symfony\\Component\\HttpFoundation\\Response::setDate` accept any
     object that implements ``\DateTimeInterface``, including immutable date objects.