[mikaraento]

RFC 9413 referenced in a parent mentions HTML. It points out that formats meant to be human-authored may benefit more from being liberally accepted.

I also read that XHTML made template authoring hard, as the template itself might not be valid XHTML and/or different template inputs might make output invalid. (I sadly can't find the source of this point right now, but I can't claim credit for it).

[int_19h]

I don't recall XHTML being harder to generate from PHP and ASP templates. It's largely down to making sure that all tags in the output are always balanced, which isn't difficult at all.

With PHP specifically there was an issue where the use of shorthand <? syntax for code snippets would conflict with <?xml declaration that would normally be placed at the beginning of the XHTML document - it would see the <? and try to interpret the rest of it as PHP code, which obviously didn't work. The workaround was to disable short tags and always use <?php explicitly