Issue #3471588 - Add new permission

fapiv_example/fapiv_example.permissions.yml

+fapiv access example page:
+  title: 'Access an example page'
+  description: 'Allows a user to access an example page.'

fapiv_example/fapiv_example.routing.yml

@@ -4,4 +4,4 @@ fapiv_example.simple_form:
     _title: 'FAPI Validation Form Example'
     _form: '\Drupal\fapiv_example\Form\SimpleForm'
   requirements:
-    _permission: 'access content'
+    _permission: 'fapiv access example page'

fapiv_example/src/Form/SimpleForm.php

@@ -41,6 +41,7 @@ class SimpleForm extends FormBase {
       '#description' => $this->t('The Value should be JonhDoe.'),
       '#validators' => [
         ['rule' => 'length[7]', 'error' => 'Wrong name size of field %field.'],
+        'custom_validator',
       ],
       '#required' => TRUE,
     ];