feature #4879 Documented true regex (WouterJ)

This PR was merged into the 2.7 branch.

Discussion
----------

Documented true regex

| Q   | A
| --- | ---
| Doc fix? | no
| New docs? | yes (symfony/symfony#11129)
| Applies to | 2.7+
| Fixed tickets | -

Commits
-------

6e6bae8 Small grammar-ish fix
050f7ce Documented true regex

components/console/helpers/questionhelper.rst

@@ -41,6 +41,24 @@ The second argument to
 is the default value to return if the user doesn't enter any input. Any other
 input will ask the same question again.
 
+.. tip::
+
+    You can customize the regex used to check if the answer means "yes" in the
+    third argument of the constructor. For instance, to allow anything that
+    starts with either ``y`` or ``j``, you would set it to::
+
+        $question = new ConfirmationQuestion(
+            'Continue with this action?',
+            false,
+            '/^(y|j)/i'
+        );
+
+    The regex defaults to ``/^y/i``.
+
+    .. versionadded:: 2.7
+        The regex argument was introduced in Symfony 2.7. Before, only answers
+        starting with ``y`` were considered as "yes".
+
 Asking the User for Information
 -------------------------------