Issue #2874067 by kkalashnikov, Nikolay Shapovalov, quietone, b_sharpe,...

 * Example:

 * @code

 * // A cache item with nodes, users, and some custom module data.

 * $tags = array(

 * $tags = [

 *   'my_custom_tag',

 *   'node:1',

 *   'node:3',

 *   'user:7',

 * );

 * ];

 * \Drupal::cache()->set($cid, $data, CacheBackendInterface::CACHE_PERMANENT, $tags);

 *

 * // Invalidate all cache items with certain tags.

 * \Drupal\Core\Cache\Cache::invalidateTags(array('user:1'));

 * \Drupal\Core\Cache\Cache::invalidateTags(['user:1']);

 * @endcode

 *

 * Drupal is a content management system, so naturally you want changes to your

 *

 *   public function buildForm(array $form, FormStateInterface $form_state) {

 *     // Create a $form API array.

 *     $form['phone_number'] = array(

 *     $form['phone_number'] = [

 *       '#type' => 'tel',

 *       '#title' => $this->t('Your phone number'),

 *     );

 *     $form['save'] = array(

 *     ];

 *     $form['save'] = [

 *       '#type' => 'submit',

 *       '#value' => $this->t('Save'),

 *     );

 *     ];

 *     return $form;

 *   }

 *

 * $form = \Drupal::formBuilder()->getForm('Drupal\my_module\Form\ExampleForm', $extra);

 * ...

 * public function buildForm(array $form, FormStateInterface $form_state, $extra = NULL)

 *   $form['phone_number'] = array(

 *   $form['phone_number'] = [

 *     '#type' => 'tel',

 *     '#title' => $this->t('Your phone number'),

 *     '#value' => $extra,

 *   );

 *   ];

 *   return $form;

 * }

 * @endcode

 * Ajax response. This is done in the text field form array element

 * in \Drupal\config_translation\FormElement\DateFormat::getFormElement():

 * @code

 * '#ajax' => array(

 * '#ajax' => [

 *   'callback' => 'Drupal\config_translation\FormElement\DateFormat::ajaxSample',

 *   'event' => 'keyup',

 *   'progress' => array(

 *   'progress' => [

 *     'type' => 'throbber',

 *     'message' => NULL,

 *   ),

 * ),

 *   ],

 * ],

 * @endcode

 *

 * As you can see from this example, the #ajax property for a form element is

 * 'wrapper' method and return HTML markup. This is not the case if you return

 * commands, but if you would like to show status messages, you can add

 * @code

 * array('#type' => 'status_messages')

 * ['#type' => 'status_messages']

 * @endcode

 * to a render array, use \Drupal::service('renderer')->render() to render it,

 * and add a command to place the messages in an appropriate location.

 *   @code

 *   public static function getSubscribedEvents() {

 *     // Subscribe to kernel terminate with priority 100.

 *     $events[KernelEvents::TERMINATE][] = array('onTerminate', 100);

 *     $events[KernelEvents::TERMINATE][] = ['onTerminate', 100];

 *     // Subscribe to kernel request with default priority of 0.

 *     $events[KernelEvents::REQUEST][] = array('onRequest');

 *     $events[KernelEvents::REQUEST][] = ['onRequest'];

 *     return $events;

 *   }

 *   @endcode

 * into a table. The table must have an ID attribute set and it

 * may be set as follows:

 * @code

 * $table = array(

 * $table = [

 *   '#type' => 'table',

 *   '#header' => $header,

 *   '#rows' => $rows,

 *   '#attributes' => array(

 *   '#attributes' => [

 *     'id' => 'my-module-table',

 *   ),

 * );

 *   ],

 * ];

 * return \Drupal::service('renderer')->render($table);

 * @endcode

 *

 * In a situation where a single weight column is being sorted in the table, the

 * classes could be added like this (in the theme function):

 * @code

 * $form['my_elements'][$delta]['weight']['#attributes']['class'] = array('my-elements-weight');

 * $form['my_elements'][$delta]['weight']['#attributes']['class'] = ['my-elements-weight'];

 * @endcode

 *

 * Each row of the table must also have a class of "draggable" in order to

 * enable the drag handles:

 * @code

 * $row = array(...);

 * $rows[] = array(

 * $row = [...];

 * $rows[] = [

 *   'data' => $row,

 *   'class' => array('draggable'),

 * );

 *   'class' => ['draggable'],

 * ];

 * @endcode

 *

 * When tree relationships are present, the two additional classes

 *

 * Calling drupal_attach_tabledrag() would then be written as such:

 * @code

 * drupal_attach_tabledrag('my-module-table', array(

 * drupal_attach_tabledrag('my-module-table', [

 *   'action' => 'order',

 *   'relationship' => 'sibling',

 *   'group' => 'my-elements-weight',

 * );

 * ];

 * @endcode

 *

 * In a more complex case where there are several groups in one column (such as

 * the block regions on the admin/structure/block page), a separate subgroup

 * class must also be added to differentiate the groups.

 * @code

 * $form['my_elements'][$region][$delta]['weight']['#attributes']['class'] = array('my-elements-weight', 'my-elements-weight-' . $region);

 * $form['my_elements'][$region][$delta]['weight']['#attributes']['class'] = ['my-elements-weight', 'my-elements-weight-' . $region];

 * @endcode

 *

 * The 'group' option is still 'my-element-weight', and the additional

 *

 * @code

 * foreach ($regions as $region) {

 *   drupal_attach_tabledrag('my-module-table', array(

 *   drupal_attach_tabledrag('my-module-table', [

 *     'action' => 'order',

 *     'relationship' => 'sibling',

 *     'group' => 'my-elements-weight',

 *     'subgroup' => 'my-elements-weight-' . $region,

 *   ));

 *   ]);

 * }

 * @endcode

 *

 * index is not sufficient, and supporting this would make the

 * "helper" too complicated and cumbersome to be of any help.

 *

 * As usual with functions that can return array() or FALSE, do not

 * As usual with functions that can return [] or FALSE, do not

 * forget to use === and !== if needed.

 *

 * @param $element

 *

 * Example:

 * @code

 * $batch = array(

 * $batch = [

 *   'title' => t('Exporting'),

 *   'operations' => array(

 *     array('my_function_1', array($account->id(), 'story')),

 *     array('my_function_2', array()),

 *   ),

 *   'operations' => [

 *     ['my_function_1', [$account->id(), 'story']],

 *     ['my_function_2', []],

 *   ],

 *   'finished' => 'my_finished_callback',

 *   'file' => 'path_to_file_containing_my_functions',

 * );

 * ];

 * batch_set($batch);

 * // Only needed if not inside a form _submit handler.

 * // Setting redirect in batch_process.

 *   }

 *   $limit = 5;

 *   $result = \Drupal::database()->select('example')

 *     ->fields('example', array('id'))

 *     ->fields('example', ['id'])

 *     ->condition('id', $context['sandbox']['current_id'], '>')

 *     ->orderBy('id')

 *     ->range(0, $limit)

 *   \Drupal::messenger()->addMessage($message);

 *   // Providing data for the redirected page is done through the session.

 *   foreach ($results as $result) {

 *     $items[] = t('Loaded node %title.', array('%title' => $result));

 *     $items[] = t('Loaded node %title.', ['%title' => $result)];

 *   }

 *   $session = \Drupal::getRequest()->getSession();

 *   $session->set('my_batch_results', $items);

 *     callback_batch_operation() and an array of parameter.

 *     Example:

 *     @code

 *     array(

 *       array('callback_batch_operation_1', array($arg1)),

 *       array('callback_batch_operation_2', array($arg2_1, $arg2_2)),

 *     )

 *     [

 *       ['callback_batch_operation_1', [$arg1)],

 *       ['callback_batch_operation_2', [$arg2_1, $arg2_2]],

 *     ]

 *     @endcode

 *   - title: A safe, translated string to use as the title for the progress

 *     page. Defaults to t('Processing').

 *   are dumped up to a stdClass object. The object can have value, required

 *   and comment properties.

 *   @code

 *   $settings['settings']['config_sync_directory'] = (object) array(

 *   $settings['settings']['config_sync_directory'] = (object) [

 *     'value' => 'config_hash/sync',

 *     'required' => TRUE,

 *   );

 *   ];

 *   @endcode

 *   gets dumped as:

 *   @code

 *     - Any HTML attributes, such as "colspan", to apply to the table cell.

 *     Here's an example for $rows:

 *     @code

 *     $rows = array(

 *     $rows = [

 *       // Simple row

 *       array(

 *       [

 *         'Cell 1', 'Cell 2', 'Cell 3'

 *       ),

 *       ],

 *       // Row with attributes on the row and some of its cells.

 *       array(

 *         'data' => array('Cell 1', array('data' => 'Cell 2', 'colspan' => 2)), 'class' => array('funky')

 *       ),

 *     );

 *       [

 *         'data' => ['Cell 1', ['data' => 'Cell 2', 'colspan' => 2]], 'class' => ['funky']

 *       ],

 *     ];

 *     @endcode

 *   - footer: An array of table rows which will be printed within a <tfoot>

 *     tag, in the same format as the rows element (see above).

 *       associative array of HTML attributes.

 *     Here's an example for $colgroup:

 *     @code

 *     $colgroup = array(

 *     $colgroup = [

 *       // <colgroup> with one <col> element.

 *       array(

 *         array(

 *           'class' => array('funky'), // Attribute for the <col> element.

 *         ),

 *       ),

 *       [

 *         [

 *           'class' => ['funky'], // Attribute for the <col> element.

 *         ],

 *       ],

 *       // <colgroup> with attributes and inner <col> elements.

 *       array(

 *         'data' => array(

 *           array(

 *             'class' => array('funky'), // Attribute for the <col> element.

 *           ),

 *         ),

 *         'class' => array('jazzy'), // Attribute for the <colgroup> element.

 *       ),

 *     );

 *       [

 *         'data' => [

 *           [

 *             'class' => ['funky'], // Attribute for the <col> element.

 *           ],

 *         ],

 *         'class' => ['jazzy'], // Attribute for the <colgroup> element.

 *       ],

 *     ];

 *     @endcode

 *     These optional tags are used to group and set properties on columns

 *     within a table. For example, one may easily group three columns and