femto113 parent
I think this would have been great if done from the beginning, but even in early versions of Mosaic malformed HTML would still appear "correct" visually, and since once it looked ok most people figured it was ok we've been buried under broken HTML from the beginning. The idea that the browser "handles every site without a problem" is slightly misleading though, since even if everything looks ok the user is paying a price of lower performance and a slower pace of innovation as browser developers devote huge amounts of time, money, and attention to not puking on all that broken HTML.
To a large degree this is it. Nobody bats an eye if a misplaced quote somewhere in a Python program causes the whole program to fail to start, but XHTML breaking pages on syntax errors was considered a terrible idea because the old way worked fine(tm).
However, Python source code is not typically dynamically generated, while HTML is, increasing the probability of errors the site author could not trivially predict and the user can do nothing about.