[jontro]

To me it’s a bit ambiguous if the original question is about both html and xhtml. It’s tagged with both

[goto11]

The headline says XHTML. HTML does not even have the self-closing tags the question is concerned about.

[jameshart]

The headline said that the author was specifically looking to avoid 'xhtml self-contained tags', but that doesn't mean they could assume the document they were looking in was valid XHTML - just that it might contain XHTML-style 'self-closing' tags.

I've seen plenty of plain HTML files that aren't well-formed XML yet contain <br/> tags.