Comment by RadiozRadioz

> It works just the same as it always has for users

No it doesn't. An HTML page constructed with XSLT written 10 years ago will suddenly break when browsers remove XSLT. The webmaster needs to add the polyfill themselves. If the webmaster doesn't do that, then the page breaks.

From a user perspective, it only remains the same as before if the webmaster adopts the polyfill. From the web developer perspective, this is a breaking change that requires action. "shipping the polyfill" requires changes on many many sites - some of which have not needed to change in many years.

It may also be difficult to do. I'm not sure what their proposed solution is, but often these are static XML files that include an XSLT stylesheet - difficult to put JS in there.