Well, hopefully the changes between versions aren't too big, because at some point it doesn't make sense to consider them to be the same language. The idea is

Well, hopefully the changes between versions aren't too big, because at some point it doesn't make sense to consider them to be the same language. The idea is that each version would still be translated into a common internal representation pretty early on after parsing, so it would almost be like supporting multiple versioned mime-types in a REST API. And it's probably harder to do with languages that already exist, but if the spec is defined from the start with versioning in mind, then it might not be so difficult.