diff --git a/core/modules/editor/src/EditorXssFilter/Standard.php b/core/modules/editor/src/EditorXssFilter/Standard.php
index aed9f29..43ef797 100644
--- a/core/modules/editor/src/EditorXssFilter/Standard.php
+++ b/core/modules/editor/src/EditorXssFilter/Standard.php
@@ -97,6 +97,12 @@ public static function filterXss($html, FilterFormatInterface $format, FilterFor
 
   /**
    * Applies a very permissive XSS/HTML filter to data-attributes.
+   *
+   * @param string $html
+   *   The string to apply the data-attributes filtering to.
+   *
+   * @return string
+   *   The filtered string.
    */
   protected static function filterXssDataAttributes($html) {
     if (stristr($html, 'data-') !== FALSE) {
diff --git a/core/modules/filter/src/Tests/FilterUnitTest.php b/core/modules/filter/src/Tests/FilterUnitTest.php
index 7a55beb..d2b515b 100644
--- a/core/modules/filter/src/Tests/FilterUnitTest.php
+++ b/core/modules/filter/src/Tests/FilterUnitTest.php
@@ -232,8 +232,7 @@ function testCaptionFilter() {
     $input = '<img data-caption="Source:Wikipedia" src="llama.jpg" />';
     $expected = '<figure><img src="llama.jpg" /><figcaption>Source:Wikipedia</figcaption></figure>';
     $this->assertIdentical($expected, $test_with_html_filter($input));
-    $expected_xss_filtered = '<img data-caption="Source:Wikipedia" src="llama.jpg" />';
-    $this->assertIdentical($expected_xss_filtered, $test_editor_xss_filter($input));
+    $this->assertIdentical($input, $test_editor_xss_filter($input));
 
     // A pretty crazy edge case where we have two colons.
     $input = '<img data-caption="Interesting (Scope resolution operator ::)" src="llama.jpg" />';