diff -r 490d5cc509ed -r cf61fcea0001 wp/wp-includes/class-wp-ajax-response.php
--- a/wp/wp-includes/class-wp-ajax-response.php	Tue Jun 09 11:14:17 2015 +0000
+++ b/wp/wp-includes/class-wp-ajax-response.php	Mon Oct 14 17:39:30 2019 +0200
@@ -1,6 +1,6 @@
 <?php
 /**
- * Send XML response back to AJAX request.
+ * Send XML response back to Ajax request.
  *
  * @package WordPress
  * @since 2.1.0
@@ -15,7 +15,7 @@
 	public $responses = array();
 
 	/**
-	 * Constructor - Passes args to {@link WP_Ajax_Response::add()}.
+	 * Constructor - Passes args to WP_Ajax_Response::add().
 	 *
 	 * @since 2.1.0
 	 * @see WP_Ajax_Response::add()
@@ -28,26 +28,37 @@
 	}
 
 	/**
-	 * Append to XML response based on given arguments.
+	 * Appends data to an XML response based on given arguments.
 	 *
-	 * The arguments that can be passed in the $args parameter are below. It is
-	 * also possible to pass a WP_Error object in either the 'id' or 'data'
-	 * argument. The parameter isn't actually optional, content should be given
-	 * in order to send the correct response.
+	 * With `$args` defaults, extra data output would be:
 	 *
-	 * 'what' argument is a string that is the XMLRPC response type.
-	 * 'action' argument is a boolean or string that acts like a nonce.
-	 * 'id' argument can be WP_Error or an integer.
-	 * 'old_id' argument is false by default or an integer of the previous ID.
-	 * 'position' argument is an integer or a string with -1 = top, 1 = bottom,
-	 * html ID = after, -html ID = before.
-	 * 'data' argument is a string with the content or message.
-	 * 'supplemental' argument is an array of strings that will be children of
-	 * the supplemental element.
+	 *     <response action='{$action}_$id'>
+	 *      <$what id='$id' position='$position'>
+	 *          <response_data><![CDATA[$data]]></response_data>
+	 *      </$what>
+	 *     </response>
 	 *
 	 * @since 2.1.0
 	 *
-	 * @param string|array $args Override defaults.
+	 * @param string|array $args {
+	 *     Optional. An array or string of XML response arguments.
+	 *
+	 *     @type string          $what         XML-RPC response type. Used as a child element of `<response>`.
+	 *                                         Default 'object' (`<object>`).
+	 *     @type string|false    $action       Value to use for the `action` attribute in `<response>`. Will be
+	 *                                         appended with `_$id` on output. If false, `$action` will default to
+	 *                                         the value of `$_POST['action']`. Default false.
+	 *     @type int|WP_Error    $id           The response ID, used as the response type `id` attribute. Also
+	 *                                         accepts a `WP_Error` object if the ID does not exist. Default 0.
+	 *     @type int|false       $old_id       The previous response ID. Used as the value for the response type
+	 *                                         `old_id` attribute. False hides the attribute. Default false.
+	 *     @type string          $position     Value of the response type `position` attribute. Accepts 1 (bottom),
+	 *                                         -1 (top), html ID (after), or -html ID (before). Default 1 (bottom).
+	 *     @type string|WP_Error $data         The response content/message. Also accepts a WP_Error object if the
+	 *                                         ID does not exist. Default empty.
+	 *     @type array           $supplemental An array of extra strings that will be output within a `<supplemental>`
+	 *                                         element as CDATA. Default empty array.
+	 * }
 	 * @return string XML response.
 	 */
 	public function add( $args = '' ) {
@@ -137,7 +148,7 @@
 		foreach ( (array) $this->responses as $response )
 			echo $response;
 		echo '</wp_ajax>';
-		if ( defined( 'DOING_AJAX' ) && DOING_AJAX )
+		if ( wp_doing_ajax() )
 			wp_die();
 		else
 			die();