> No they didn’t, unless you and I have wildly different definitions of “a fair amount”. The developers who did that were an extreme minority because Internet Explorer, which had >90% market share, didn’t support application/xhtml+xml. It was a curiosity, not something people actually did in non-negligible numbers.
Despite being an extreme minority of strict parsing enthusiasts who decided to explicitly opt into strict parsing, they still messed up enough for me to occasionally have encountered "XML Parse Error" pages. You'd think that if anyone managed to correctly generate strict XHTML, it'd be those people.
