form

$form['advanced'] = array(
 '#type' => 'details',
 '#title' => t('Advanced settings'),
 '#description' => t('Lorem ipsum.'),
 '#open' => TRUE, // Controls the HTML5 'open' attribute.

<?php
namespace Drupal\mymodule\Plugin\Block;
use Drupal\Core\Block\BlockBase;
use Drupal\Co

/**
 * {@inheritdoc}
 */
public function buildForm(array $form, FormStateInterface $form_state) {
 $form['actions'] = [
   '#type' => 'actions',
 ];
 if ($markup = $form_state->get(

/** @var \Drupal\Core\Entity\EntityForm $form_object */
$form_object = $form_state->getFormObject();
if ($form_object instanceof EntityForm) {
  $entity = $form_object->getEntity();
  // Do something with the entity.
}

/**
* Implements hook_form_FORM_ID_alter().
*/
function mymodule_form_user_register_form_alter(&$form, FormStateInterface $form_state, $form_id) {
 $form['actions']['submit']['#submit'][] = '_mymodule_user_register_form_submit';
}

/**
 * Import categories batch.
 */
public static function importCategories($arg1, $arg2, &$context) {
 $a = 1;
}
/**
 * {@inheritdoc}
 */
public 

/**
* {@inheritdoc}
*/
public function buildForm(array $form, FormStateInterface $form_state) {
  $validators = [
    'file_validate_extensions' => ['xml'],
  ];
  $form['upload'] = [
    '#type'

/**
 * The entity type manager.
 *
 * @var \Drupal\Core\Entity\EntityTypeManagerInterface
 */
protected $entityTypeManager;
/**
 * The form constructor.
 *
 * @param \Drupal\Core\Entity\EntityTypeManagerInterface $entity_type_manager
 *   The entity type manager.
 */
public function