only in patch2:
unchanged:
--- a/core/lib/Drupal/Core/Routing/RedirectDestinationInterface.php
+++ b/core/lib/Drupal/Core/Routing/RedirectDestinationInterface.php
@@ -38,6 +38,11 @@ public function getAsArray();
    * @endcode
    *
    * @return string
+   *   The value of the current request's 'destination' query
+   *   parameter, if present. This can be either a relative or absolute URL.
+   *   However, for security, redirection to external URLs is not performed.
+   *   If the query parameter isn't present, then the URL of the current
+   *   request is returned.
    */
   public function get();