diff --git a/core/lib/Drupal/Component/Utility/String.php b/core/lib/Drupal/Component/Utility/String.php
index 3cd6472..7dba3fa 100644
--- a/core/lib/Drupal/Component/Utility/String.php
+++ b/core/lib/Drupal/Component/Utility/String.php
@@ -72,7 +72,7 @@ public static function decodeEntities($text) {
    *   - @variable: Escaped to HTML using String::checkPlain(). Use this as the
    *     default choice for anything displayed on a page on the site.
    *   - %variable: Escaped to HTML and formatted using String::placeholder(),
-   *     which makes it display as <em>emphasized</em> text.
+   *     which makes it display as <em class="placeholder">emphasized</em> text.
    *   - !variable: Inserted as is, with no sanitization or formatting. Only use
    *     this for text that has already been prepared for HTML display (for
    *     example, user-supplied text that has already been run through