&gt; That something is used does not mean it is legitimate.<p>While I agree, in practice what this means is that either all browsers need to coordinate rollout precisely (and even then the result will be that many users just stay on insecure versions of browsers instead of updating) or you will have pages (or employers) telling users to switch to whatever browser lags in rolling this out.<p>We&#x27;ve seen this play out before.  The result is that you end up with users picking whichever browser defects (which reduces the incentive for other browsers to do this) or being stuck on the equivalent of IE6.<p>The benefit of changes that do NOT break compat is that browsers can just roll them out without needing to worry about the above side-effects.