When the web was young, it was fine if people missed a tag somewhere, or mis-nested tags, or did other mistakes. The browsers were forgiving. Moreover, the stan

When the web was young, it was fine if people missed a tag somewhere, or mis-nested tags, or did other mistakes. The browsers were forgiving. Moreover, the standard was forgiving. This is useful when you want mass adoption. It makes early adopters' lives easy and increases spread. It's been a long while since those times. We have validators, editors that match tags, tools that write markup for you and other fancy gadgets, and people whose professions contain a good amount of markup-writing. You know what? It's not acceptable to not conform anymore. Too much effort is spent on trying to make meaning out of peoples' broken markup, rendering pages that shouldn't normally be rendered. Even the major browser vendors can't decide how standards compliant markup should be rendered, only recently has there been visible improvement. It's not that the vendors are dumb or unable, it's that their job is difficult because of the giant kludge they have to work with. XML is "elegant" compared to HTML in the sense that it's uniform, it's consistent, kinda like lisp syntax. Parsing it is easy. This is even more important with all the talk of the "semantic web". Notice how difficult it is to extract meaning out of natural language, and how natural language has non-uniform (or very complicated) grammar. Now notice how simple, in comparison, it is to extract meaning out of something with a small and simple grammar, such as a small programming language. This is what we want. The point is, once we fix the infrastructure, we can add new functionality as needed. XHTML might not have a canvas tag and HTML may, but what's to happen if in the future we decide that we need some other extension? We revise the whole standard? Ridiculous.