Issue #3455342 by vladimiraus, bharath-kondeti, smustgrave: Improve...

/**

 * AJAX command for a JavaScript Drupal.message() call.

 *

 * Developers should be extra careful if this command and

 * \Drupal\Core\Ajax\AnnounceCommand are included in the same response. Unless

 * the `announce` option is set to an empty string (''), this command will

 * result in the message being announced to screen readers. When combined with

 * AnnounceCommand, this may result in unexpected behavior. Manual testing with

 * a screen reader is strongly recommended.

 * AJAX command that allows you to add messages from an Ajax response. The command will create a new Drupal.Message() object and call its addMessage() method.

 *

 * Usage examples:

 * Here are examples of how to suppress announcements:

 * @code

 *   $response = new AjaxResponse();

 *

 *   // A status message added in the default location.

 *   $response->addCommand(new MessageCommand('Your changes have been saved.'));

 *

 *   // A warning message added in the default location.

 *   $response->addCommand(new MessageCommand('There was a problem. Save your work.', NULL, ['type' => 'warning']));

 *

 *   // A status message added an alternate location.

 *   $response->addCommand(new MessageCommand('Hey look over here!', '#alternate-message-container'));

 *

 *   // An error added in an alternate location.

 *   $response->addCommand(new MessageCommand('Open the pod bay doors, HAL.',  '#alternate-message-container', ['type' => 'error']));

 * @endcode

 *

 * By default, previous messages in a location are cleared before the message

 * is added. If you would like to leave the previous messages in a location,

 * you may do so by setting the fourth parameter to FALSE:

 * Here are examples of how to suppress announcements:

 * @code

 *   $response->addCommand(new MessageCommand('Hey look over here.', NULL, ['type' => 'error'], FALSE));

 * @endcode

 *

 * Developers should take care when using MessageCommand and AnnounceCommand 

 * together in the same AJAX response. Unless the "announce" option is set to

 * an empty string (''), this command will result in the message being

 * announced to screen readers. When combined with AnnounceCommand, this may

 * result in unexpected behavior. Manual testing with a screen reader is

 * strongly recommended.

 *

 * If you wish to display a message without the text being announced to screen

 * readers, add options.announce = '' (i.e. an empty string):

 * @code

 *   $command = new MessageCommand("I won't be announced", NULL, [

 *     'announce' => '',

 *   ]);

 * @endcode

 *

 * If you wish to set the announcement priority to assertive, you can do that

 * this way: 

 * @code

 *   $response->addCommand(new MessageCommand('You added 3 cat pics.', '.js-media-library-messages', [

 *     'priority' => 'assertive',

 *   ]);

 * @endcode

 *

 * @see \Drupal\Core\Ajax\AnnounceCommand

 * @see https://www.drupal.org/docs/develop/drupal-apis/ajax-api/core-ajax-callback-commands#s-messagecommand

 *

 * @ingroup ajax

 */