Needs-Triage-M123

Tried to reproduce the issue on reported chrome version #123.0.6312.59 using Linux debian as per steps mention in comment #1

Steps to reproduce :-
==============
1.Launched Google chrome
2.Opened the "data:application/xhtml+xml,<div xmlns="http://www.w3.org/1999/xhtml"><template shadowrootmode="open">OpenDeclarativeShadowDOMsupported</template></div>"

Attaching screencast for reference

Reporter:-Could you please review the attached screenscast and let us know if we missed anything from our endand also requesting to provide a screencast of actual and expected behaviour for better understanding of the issue.

Thanks..!!

Hello there,

Thank you for looking into this. It looks like you are reproducing the bug, but I might not have explained the situation very well.

I've attached my own screencast demonstrating the bug which I'll walk through here:

1. Launch Chromium
2. Paste the following into the URL bar (note the XHTML mimetype, making this an XHTML page):
   data:application/xhtml+xml,<div xmlns="http://www.w3.org/1999/xhtml"><template shadowrootmode="open">OpenDeclarativeShadowDOMsupported</template></div>
3. See that the page remains blank and in the web inspector the declarative shadow DOM has not been created (the <template> has not be substituted with a shadow-root etc.)
4. Now, to see the expected behaviour, change the mimetype in the URL to plain HTML (i.e. replace `application/xhtml+xml` with `text/html` making the page now a plain HTML page)
5. Notice that page now shows the "OpenDeclarativeShadowDOMsupported" message and the DOM inspector now show a newly created shadow root.

Unless I'm mistaken, what is shown here is that the declarative shadow DOM mechanism will only work for plain HTML pages and not for XHTML pages. As far as I understand, there is no reason that an XHTML page should not be able to make use of the declarative shadow DOM syntax.

Thanks again for your help,

Jonathan

Thank you for providing more feedback. Adding the requester to the CC list.

Able to reproduce this issue on chrome version #123.0.6312.59 using win 10,Mac 14.3.1,Linux debian  by following steps as per comment#0
Observed the page remains blank

Reproducible on
=============
125.0.6382.0 - Canary
125.0.6368.2- Dev
124.0.6367.8 - Beta
123.0.6312.59 -Stable

Attached screenshots for reference

The same issue seems to be reproducible from M-112 older versions. Hence, considering it as Non-Regression and marking it as untriaged

Thanks..!!

Mason, is there a plan to support this?

I don't believe this is correct, though I think this may be my fault for using somewhat dated terminology.

The spec specifically doesn't use the term XHTML any more, using only "HTML" to refer to the things which are defined via the HTML syntax, the XML Syntax for HTML (what I, sloppily, called XHTML) and defined via the DOM API. See https://html.spec.whatwg.org/multipage/introduction.html#html-vs-xhtml

As such, I believe the spec you linked to applies in this case, even though it talks about HTML. For example it even mentions namespaces (a feature called out as not supported by the HTML syntax in the introduction I linked to).

Would you agree?

...though, hmm... rereading this again, as you say, it seems declarative shadow DOM does seem to be a side effect of HTML-specific parsing, so you're a absolutely right...

Would you concur that this seems like a bit of a design error (or at least a bit wonky?)

Thanks again for the thorough analysis.

For reference, I've opened the following issue: https://github.com/whatwg/html/issues/10237