Isn&#x27;t that basically what we did with doctypes?  HTML has a lot of similar issues and it has slowly managed to move forward.  The real benefit was not having to mix old and new code and getting rid of all the quirks by requiring you specify that you want them if you want that old doc to work.<p>JavaScript could get to the same place just be letting you specify a different language in the script tag.<p>The big question is how we support legacy browsers for a time because many won&#x27;t support the new keywords.