Hi Hilmar - well, I agree it is a bug, since html4 is being requested. Unfortunately <br /> and <hr /> are ubiquitious in tex4ht-html4.tex; I guess Eitan didn't know about the problem.

It does not seem straightforward at all to factor them all out so they are conditional on html4. And I believe all that code is used for other html variants, so just removing the slashes would mean xhtml output etc. would no longer validate, so that's not viable.

Since html5 is pretty widespread by now, it's hard for me and Michal to work up a lot of enthusiasm for tinkering with the html4 output. I know that's sad, but there it is. Of course reasonable patches would be welcome (good luck :).

I'm not sure about this, Michal. If it's only claiming to be "traditional" HTML, not XHTML or HTML5, those XML-ish statements actually break browsers and validation. I've tried to add <hr/> and the like to plain HTML before, and it didn't work out well.

https://bugs.debian.org/536380
Hope the bug is still valid.

Command used:
mk4ht htlatex manual-web.tex "html,uni-html4,frames,css2,charset=utf-8,info" " -cunihtf -utf8"

Despite not having any XHTML or XML options enabled, it is outputting various bits of XML:

<br />
<hr class="endfloat" />
<br class="newline" />

Minimal exmample for the <br /> part:

\documentclass{article}
\begin{document}

Hello,\\
world
\end{document}
-----
Thanks!