UV incompatible with XHTML 5

[Conal-Tuohy]

UV version:

 universalviewer@3.0.36

I'm submitting a:

• [x] bug report
• [ ] feature request => please use the user stories repo
• [ ] support request => Please do not submit support requests here, use stackoverflow

Current behavior:

When UV is hosted in an XHTML 5 page, the contents panel remains empty, and Javascript exceptions are thrown in the console. Expected behavior:

UV should work equally well when hosted in an HTML 5 or an XHTML 5 page. Steps to reproduce:

Related code:

// insert any relevant code here

Other information:

See discussion in Slack and my PR #677 which partially addresses the issue.

[LlGC-szw]

All issues will be triaged for further investigation or closure by the 28 September 2023. If your issue is still relevant and would like for it be investigated further please comment by 14 September 2023.

[Conal-Tuohy]

I think XHTML5 compatibility is still worth having.

Note that at least some of the problems I originally had with embedding UV in an XHTML page were due to errors in the HTML markup which UV produced, which were errors in both HTML5 and XHTML5, and led to actual defects in functionality which were being unnoticed and weren't flagged by browsers in HTML5 mode because of the tolerant parsing rules for HTML5.

The stricter rules for XML mean that targeting XHTML5 is effectively a way to find errors and improve code quality.