Issue #3252587 by longwave, smustgrave, Chalk, borisson_, alexpott: Extend the $skip_protocol_filtering list of attributes to use Tailwind CSS classes with prefix ":"

core/lib/Drupal/Component/Utility/Xss.php

@@ -237,6 +237,7 @@ class Xss {
               'alt',
               'rel',
               'property',
+              'class',
             ]);
 
             $working = $mode = 1;

core/tests/Drupal/Tests/Component/Utility/XssTest.php

@@ -504,8 +504,8 @@ class XssTest extends TestCase {
   public function providerTestAttributes() {
     return [
       [
-        '<img src="http://example.com/foo.jpg" title="Example: title" alt="Example: alt">',
-        '<img src="http://example.com/foo.jpg" title="Example: title" alt="Example: alt">',
+        '<img src="http://example.com/foo.jpg" title="Example: title" alt="Example: alt" class="md:block">',
+        '<img src="http://example.com/foo.jpg" title="Example: title" alt="Example: alt" class="md:block">',
         'Image tag with alt and title attribute',
         ['img'],
       ],