CKEditor5 rendering is stripping nested HTML content, providing data loss for user

[kevinlin98z]

📝 Provide detailed reproduction steps (if any)

1. Have CKEditor5 render the following payload:

<div>Dear Andy Coffey,</div><div>&nbsp;</div><div><span style=\"color:#000000; display:inline!important; float:none; font-family:&quot;Times New Roman&quot;; font-size:medium; font-style:normal; font-weight:400; letter-spacing:normal; text-align:start; text-decoration-color:initial; text-decoration-style:initial; text-indent:0px; text-transform:none; word-spacing:0px\">Thereference case number for this solution is:<span>&nbsp;</span></span><span style=\"font-size:11.0pt\"><span style=\"line-height:107%\"><span style=\"font-family:&quot;Calibri&quot;,sans-serif\"><span style=\"color:black\">3000373510</span></span></span></span></div><div><span style=\"color:#000000; display:inline!important; float:none; font-family:&quot;Times New Roman&quot;; font-size:medium; font-style:normal; font-weight:400; letter-spacing:normal; text-align:start; text-decoration-color:initial; text-decoration-style:initial; text-indent:0px; text-transform:none; word-spacing:0px\">Byanalyzing the system service logs uploaded by you we propose the following solution:</span></div><div>&nbsp;</div><div> <div><b>Action Plan:</b></div><br> We found 1 issue in FFDC file (7Z71CTO1WW_J30A09H2_xcc_mini-log_20240509-144330.zip):<br> <ul> <li> One event occurred on CMOS Battery at 2024-05-09T10:26:44Z.</li> </ul> We suggest following actions:<br><br> For event FQXSPPW0031J, \"Numeric sensor CMOS Battery going low (lower non-critical) has asserted.\", 2024-05-09T10:26:44Z<br> <ul> Complete the following steps until the problem is solved:<br>1. Remove the CMOS battery for 20 seconds and then install it back.<br>2. Replace the system CMOS battery<br>3. If the issue persists, please choose \"NO\" in the subsequent emails.</ul><br> </div><div>&nbsp;</div><div><strong style=\"color:#000000; font-family:&quot;Times New Roman&quot;; font-size:medium; font-style:normal; letter-spacing:normal; text-align:start; text-decoration-color:initial; text-decoration-style:initial; text-indent:0px; text-transform:none; word-spacing:0px\"><em>Wehope that by completing the above steps, the issue will be resolved. We will send you a follow-up email in 3 days from now to check the status. Please reply to the follow-up email and we will process your case based on the response selected.</em></strong></div>

2. Notice above payload is invalid HTML here:

3. CKEditor5 renders the above payload like below:

✔️ Expected result

What is the expected result of the above steps?

CKEditor5 rendering engine should not strip invalid <ul> content without <li> elements. If data absolutely has to be stripped, user should be notified.

❌ Actual result

What is the actual result of the above steps?

CKEditor5 rendering engine removes the entire <ul> content. This presents a data loss for the user, and is a regression compared to CKEditor4, which did not do this.

❓ Possible solution

Do not strip <ul> content that does not have <li> child elements (same applies to additional nesting elements like tables too). CKEditor4 did not have this behavior.

📃 Other details

• Browser: …
• OS: …
• First affected CKEditor version: CKEditor5
• Installed CKEditor plugins: …

---

If you'd like to see this fixed sooner, add a 👍 reaction to this post.

[Witoso]

Notes:

• our CKEditor 5 converters remove all text nodes that are not in li.
• most likely we need to we need to tune the upcast to not clear the text nodes. 
• it's possible that autoparagraphing will “just work”.
• TBD if we will wrap in li or p, the goal is to not have data loss, but data change is acceptable.