> By now, HTML and the standards surrounding it have become so big that starting from a blank slate nowadays is next to impossible. One important mitigating fa

> By now, HTML and the standards surrounding it have become so big that starting from a blank slate nowadays is next to impossible. One important mitigating factor is that newer standards often generalize older ones. For example, originally all the list elements had special case handling (and still might in other engines), but now it's possible to do all that with the user agent style sheet with new additions to CSS that generalized these things. It saves an enormous amount of work to implement the web at a particular point in time as opposed to starting at the beginning and keeping up with the changes until that same point in time. Not only that, but all the failed branches that were already explored mean that a new engine avoids quite a bit of technical debt. It's still quite hard. Here's a nice example of a layout bug on HN we thought would be simple to fix for the release, but turned ugly fast: https://github.com/servo/servo/issues/11821 https://github.com/servo/servo/issues/11821