Don't try to make it a technical issue, because it totally isn't. Every single one of those files goes through a compiler of some kind. Source code gets transfo

Don't try to make it a technical issue, because it totally isn't. Every single one of those files goes through a compiler of some kind. Source code gets transformed to a tree, AST, whatever. They only thing changing here is that somewhere near the root of that tree there's a version. In many languages there is already a mechanism for specifying that kind of info, like pragmas or CDATA in SGML descended markup languages. And it's not hard to introduce either way. Javascript borrowed 'use strict' from Perl 5, for example. In the end you write something in a language. What language you use to write that isn't defined in some external file, it's an inherent property of the text. You can't write a note in Ye Olde English and expect it to be understood by modern people without issues.