class VerticalTabsDemo

class VerticalTabsDemo extends DemoBase {
    
    /**
     * Build the form.
     *
     * @inheritdoc
     */
    public function buildForm(array $form, FormStateInterface $form_state) {
        $form['description'] = [
            '#type' => 'item',
            '#markup' => $this->t('This example demonstrates the use of vertical tabs to group elements.'),
        ];
        $form['information'] = [
            '#type' => 'vertical_tabs',
            '#default_tab' => 'edit-publication',
        ];
        $form['author'] = [
            '#type' => 'details',
            '#title' => 'Author',
            '#group' => 'information',
        ];
        $form['author']['name'] = [
            '#type' => 'textfield',
            '#title' => $this->t('Name'),
        ];
        $form['publication'] = [
            '#type' => 'details',
            '#title' => $this->t('Publication'),
            '#group' => 'information',
        ];
        $form['publication']['publisher'] = [
            '#type' => 'textfield',
            '#title' => $this->t('Publisher'),
        ];
        $form['actions'] = [
            '#type' => 'actions',
        ];
        // Add a submit button that handles the submission of the form.
        $form['actions']['submit'] = [
            '#type' => 'submit',
            '#value' => $this->t('Submit'),
        ];
        return $form;
    }
    
    /**
     * Getter method for Form ID.
     *
     * @inheritdoc
     */
    public function getFormId() {
        return 'form_api_example_vertical_tabs_demo';
    }

}