Ok I have to disagree here. I believe the failure of XHTML was to cram everything into XML; I found XForms especially pointless. Now don't get me wrong, and as

Ok I have to disagree here. I believe the failure of XHTML was to cram everything into XML; I found XForms especially pointless. Now don't get me wrong, and as you know from my other posts here I'm as much of a markup geek as can be, but IMO markup is first and foremost for representing and authoring text. Just that browser content is mostly text, however, doesn't mean everything has to be markup. To the contrary, I believe XHTML (and XML in mainstream apps) fell out of favor because the spec authors tried to anchor each and everything on XML, rather than on something that makes sense for the task at hand (a phenomenon not unheard of for JSON and YAML as well). In XForms, for example, XML was used as a programming language which just never made sense. You know you're doing it wrong IMHO when you have to discuss whether you want to store your data in attributes or element content, a distinction that only makes sense for text data. It's sad and surprising how much time and energy was wasted on XHTML. Back in february I met Steven Pemberton (XHTML spec lead back then, and of ABC/Python fame). He's just such an inspiring guy to talk to, but unfortunately, there was no time for recapitulating the XHTML situation.