--- /dev/null
+<?php
+
+namespace Drupal\form_test\Form;
+
+use Drupal\Core\Form\FormBase;
+use Drupal\Core\Form\FormStateInterface;
+
+/**
+ * Builds a simple form to test the #group property on #type 'vertical_tabs'.
+ */
+class FormTestGroupVerticalTabsForm extends FormBase {
+
+ /**
+ * {@inheritdoc}
+ */
+ public function getFormId() {
+ return 'form_test_group_vertical_tabs';
+ }
+
+ /**
+ * {@inheritdoc}
+ */
+ public function buildForm(array $form, FormStateInterface $form_state) {
+ $form['vertical_tabs'] = [
+ '#type' => 'vertical_tabs',
+ ];
+ $form['meta'] = [
+ '#type' => 'details',
+ '#title' => 'First group element',
+ '#group' => 'vertical_tabs',
+ ];
+ $form['meta']['element'] = [
+ '#type' => 'textfield',
+ '#title' => 'First nested element in details element',
+ ];
+ $form['meta_2'] = [
+ '#type' => 'details',
+ '#title' => 'Second group element',
+ '#group' => 'vertical_tabs',
+ ];
+ $form['meta_2']['element_2'] = [
+ '#type' => 'textfield',
+ '#title' => 'Second nested element in details element',
+ ];
+ return $form;
+ }
+
+ /**
+ * {@inheritdoc}
+ */
+ public function submitForm(array &$form, FormStateInterface $form_state) {
+ }
+
+}