CKEditor 5 strips out unordered list tags if field contains multiple UL classes

[steveb510]

📝 Provide detailed reproduction steps (if any)

1. A text field contains consecutive unordered lists, each with a unique class so it can be styled differently in CSS.
2. HTML validator confirms that it is valid code.

✔️ Expected result

That all ul tags are retained as coded

❌ Actual result

CKEditor5 strips out all but the first class, so items that should be styled as class2, class3, etc. are now styled as class1. See attached.

❓ Possible solution

Only solution is to disable CKEditor for fields that contain consecutive unordered lists. This is what I have done, so it's not a critical issue, but it would be nice to get a WYSIWYG preview of the field.

📃 Other details

• Browser: Firefox
• OS: Windows 11
• First affected CKEditor version: 5
• Installed CKEditor plugins: None

I'm using CKEditor5 in Backdrop CMS, which is a fork of Drupal 7.

I've attached two code samples, one showing the expected result and the other showing the actual result.

expected-result.txt
actual-result.txt

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[Reinmar]

By default CKEditor cleans up such lists. You can enable a plugin AdjacentListsSupport plugin covered in Merging adjacent lists section to change this behavior.

AFAIR, Drupal 9+ actually enables this plugin by default.