Describe validation callables

Author: W0rma

validation/callables.rst

@@ -0,0 +1,30 @@
+.. index::
+    single: Validation; Callables
+
+How to Use Validation Constraints in Callable Validation (Validation Callables)
+===============================================================================
+
+Sometimes you need to reuse Symfony's constraints in places like the Symfony Console,
+to validate the answer to a console question. ``Validation::createCallable()``
+can be used to create a callable based on the given constraints::
+
+    use Symfony\Component\Console\Style\SymfonyStyle;
+    use Symfony\Component\Validator\Constraints\NotNull;
+    use Symfony\Component\Validator\Validation;
+
+    $io = new SymfonyStyle($input, $output);
+    $validation = Validation::createCallable(new NotBlank());
+
+    $wsdl = $io->ask('Wsdl location URL', null, $validation);
+
+The argument of ``createCallable()`` is variadic, so you can pass any number of constraints::
+
+    // ...
+    use Symfony\Component\Validator\Constraints\Length;
+    use Symfony\Component\Validator\Constraints\Url;
+
+    $validation = Validation::createCallable(new Length(['max' => 255]), new Url());
+
+.. versionadded:: 5.1
+
+    ``Validation::createCallable()`` was introduced in Symfony 5.1.