diff --git a/core/modules/rest/src/Tests/Views/StyleSerializerTest.php b/core/modules/rest/src/Tests/Views/StyleSerializerTest.php
index fd890f7..0a14c3c 100644
--- a/core/modules/rest/src/Tests/Views/StyleSerializerTest.php
+++ b/core/modules/rest/src/Tests/Views/StyleSerializerTest.php
@@ -400,6 +400,6 @@ public function testFieldapiField() {
     $node->save();
     $result = $this->drupalGetJSON('test/serialize/node-field');
     $this->assertEqual($result[1]['nid'], $node->id());
-    $this->assertTrue(strpos($this->getRawContent(), "<script") === FALSE, "The Raw page contents are escaped.");
+    $this->assertTrue(strpos($this->getRawContent(), "<script") === FALSE, "No script tag is present in the raw page contents.");
   }
 }
diff --git a/core/modules/system/theme.api.php b/core/modules/system/theme.api.php
index 179d9da..bf99cef 100644
--- a/core/modules/system/theme.api.php
+++ b/core/modules/system/theme.api.php
@@ -266,10 +266,13 @@
  *   the markup is very simple, such as an explanation in a paragraph tag, it
  *   is normally preferable to use #theme or #type instead, so that the theme
  *   can customize the markup. Note that the value is passed through
- *   \Drupal\Component\Utility\XSS::filterAdmin() which allows tags that are
- *   known to be safe. I.e <script> and <style> are not allowed. If your markup
- *   needs any of the tags that are not white listed, then you should implement
- *   a theme hook and template file and/or an asset library.
+ *   \Drupal\Component\Utility\Xss::filterAdmin(), which strips known XSS
+ *   vectors while allowing a permissive list of HTML tags that are not XSS
+ *   vectors. (I.e, <script> and<style> are not allowed.) See
+ *   \Drupal\Component\Utility\Xss::$adminTags for the list of tags that will
+ *   be allowed. If your markup needs any of the tags that are not in this
+ *   whitelist, then you should implement a theme hook and template file and/or
+ *   an asset library.
  *   @see core.libraries.yml
  *   @see hook_theme()
  *