That still wasn't serious enough. All it took to get browsers to accept non-XHTML pages was to change the MIME type. What I'm talking about is simply not displaying ill-formed pages at all, under any circumstances.
But with that MIME type it wasn't XHTML at all. It was being parsed as HTML which was possible only because of big similarity between those two formats. All you need to ensure the behavior you want is to disable HTML parsing (which is pretty much ensures being liberal in what the parser accepts already in its specification).
