drupal/core/modules/serialization/serialization.module

<?php

/**
 * @file
 * Provides a service for (de)serializing data to/from formats such as JSON and XML.
 */

use Drupal\Core\Url;
use Drupal\Core\Routing\RouteMatchInterface;

/**
 * Implements hook_help().
 */
function serialization_help($route_name, RouteMatchInterface $route_match) {
  switch ($route_name) {
    case 'help.page.serialization':
      $output = '';
      $output .= '<h3>' . t('About') . '</h3>';
      $output .= '<p>' . t('The Serialization module provides a service for serializing and deserializing data to and from formats such as JSON and XML.') . '</p>';
      $output .= '<p>' . t('Serialization is the process of converting data structures like arrays and objects into a string. This allows the data to be represented in a way that is easy to exchange and store (for example, for transmission over the Internet or for storage in a local file system). These representations can then be deserialized to get back to the original data structures.') . '</p>';
      $output .= '<p>' . t('The serializer splits this process into two parts. Normalization converts an object to a normalized array structure. Encoding takes that array and converts it to a string.') . '</p>';
      $output .= '<p>' . t('This module does not have a user interface. It is used by other modules which need to serialize data, such as <a href=":rest">REST</a>.', [':rest' => (\Drupal::moduleHandler()->moduleExists('rest')) ? Url::fromRoute('help.page', ['name' => 'rest'])->toString() : '#']) . '</p>';
      $output .= '<p>' . t('For more information, see the <a href=":doc_url">online documentation for the Serialization module</a>.', [':doc_url' => 'https://www.drupal.org/documentation/modules/serialization']) . '</p>';
      return $output;
  }
}