diff --git a/core/lib/Drupal/Component/Utility/Xss.php b/core/lib/Drupal/Component/Utility/Xss.php
index 4127ef3..cf39407 100644
--- a/core/lib/Drupal/Component/Utility/Xss.php
+++ b/core/lib/Drupal/Component/Utility/Xss.php
@@ -44,7 +44,8 @@ class Xss {
    * @param array $html_tags
    *   An array of HTML tags.
    * @param bool $set_safe_markup
-   *   If TRUE call SafeMarkup::set() on result before returning it.
+   *   (optional) Defaults to TRUE and calls SafeMarkup::set() on result before
+   *   returning it.
    *
    * @return string
    *   An XSS safe version of $string, or an empty string if $string is not