// MODULENAME.module
 
/**
 * Implements hook_entity_base_field_info().
 */
function MODULENAME_entity_base_field_info(EntityTypeInterface $entity_type) {
  if ($entity_type->id() == 'taxonomy_term') {
    $fields = [];
 
    $fields['depth_level'] = BaseFieldDefinition::create('integer')
      ->setLabel(t('Depth'))
      ->setSetting('unsigned', TRUE)
      ->setDefaultValue(0);
 
    return $fields;
  }
}

/**
 * Implements hook_ENTITY_TYPE_presave(): flagging.
 */
function MODULENAME_flagging_presave(FlaggingInterface $flagging) {
  // Save user ip
  if ($flagging->hasField('field_ip')) {
    $flagging->set('field_ip', \Drupal::request()->getClientIp());

// src/Plugin/Filter/TableWrapperFilter.php
 
/**
 * @Filter(
 *   id = "table_wrapper_filter",
 *   title = @Translation("Table wrapper"),
 *   description = @Translation("Wrap tables to div."),
 *   type = Drupal\filter\Plugin\FilterInterface::TYPE_TRANSFORM_REVERSIBLE,
 *   weight = 20
 * )
 */
class TableWrapperFilter extends FilterBase {
 
  /**
   * {@inheritdoc}
   */
  public function process($text, $langcode) {
    $result = new FilterProcessResult($text);
 
    if (stristr($text, '<table') !== FALSE) {

(function ($, Drupal) {
  /**
   * Override AJAX eventResponse function.
   */
  var originalAjaxEventResponse = Drupal.Ajax.prototype.eventResponse;
 
  Drupal.Ajax.prototype.eventResponse = function (element, event) {
    var $element = $(element);

// MODULENAME.module
 
/**
 * Implements hook_field_formatter_third_party_settings_form().
 */
function MODULENAME_field_formatter_third_party_settings_form(FormatterInterface $plugin, FieldDefinitionInterface $field_definition, $view_mode, array $form, FormStateInterface $form_state) {
  $element = [];
 
  if ($plugin->getPluginId() == 'text_default') {
    $element['max_length'] = [
      '#type' => 'number',
      '#title' => t('Max length'),

# modulename.routing.yml
 
modulename.example_route:
  ...
  options:
    _admin_route: TRUE

// src/EventSubscriber/ModulenameRouteSubscriber.php
 
namespace Drupal\modulename\EventSubscriber;
 
use Drupal\Core\Routing\RouteSubscriberBase;
use Symfony\Component\Routing\RouteCollection;
 
class ModulenameRouteSubscriber extends RouteSubscriberBase {

/**
 * Preprocess function for menu--account.html.twig.
 */
function THEMENAME_preprocess_menu__account(&$vars) {
  if (\Drupal::currentUser()->isAnonymous()) {
    $login_link_url = $vars['items']['user.logout']['url']; /** @var Url $login_link_url */
    $login_link_url->mergeOptions([
      'attributes' => [
        'class' => ['use-ajax'],
        'data-dialog-type' => 'modal',
      ],
    ]);

class ExampleDraggableForm extends FormBase {
 
  /**
   * {@inheritdoc}
   */
  public function getFormId() {
    return 'example_draggable_form';
  }
 
  /**
   * {@inheritdoc}
   */
  public function buildForm(array $form, FormStateInterface $form_state) {
    $form['table'] = [
      '#type' => 'table',
      '#header' => ['Title', 'Weight'],
      '#empty' => 'Empty...',
      '#tabledrag' => [[
        'action' => 'order',
        'relationship' => 'sibling',
        'group' => 'node-weight',

class ModulenameController extends ControllerBase {
 
  public function exampleTabContent(NodeInterface $node) {
    return ['#markup' => 'Tab content...'];
  }
 
  public function exampleTabAccess(NodeInterface $node) {
    return AccessResult::allowedIf($node->bundle() === 'page');
  }
 
}

entity.node.example_tab:
  path: '/node/{node}/example-tab'
  defaults:

<?php
 
namespace Drupal\modulename\Element;
 
use Drupal\Core\Form\FormStateInterface;
use Drupal\Core\Render\Element\FormElement;
 
/**
 * @FormElement("fullname")
 */
class FullnameElement extends FormElement {
 
  /**
   * {@inheritDoc}
   */
  public function getInfo() {
    $class = get_class($this);
 
    return [
      '#input' => TRUE,
      '#process' => [
        [$class, 'processElement'],
      ],