[jancsika]

Am I correct that malformed pages in xhtml would have triggered the browser to output a red XML error and fail to render the page at all?

[Calavar]

Yes, but only if you served the XHTML with the proper MIME type of application/xhtml+xml. Nearly everyone served it as text/html, which would lead to the document being intepreted as this weird pseudo XHTML/HTML4 hybrid dialect with all sorts of brower idiosyncrasies [1].

[1] https://www.hixie.ch/advocacy/xhtml