That's my point. By the time you hit "until it doesn't", you're already doing JSON, and were for a while.

Also, is "parse well if there's a missing bracket" even a desirable property? If you get files with mangled syntax, something has already gone horribly wrong. And, chances are, there is no way to parse them that would be correct.

By "parses well" in that case I mean "can identify where the error is, and maybe even infer the missing closing tag if desirable;" i.e. error reporting and recovery.

If you've ever debugged a JSON parse error where the location of the error was the very end of a large document, and you're not sure where the missing bracket was, you'll know what I mean. (S-exprs have similar problems, BTW; LISPers rely on their editors so as not to come to grief, and things still sometimes go pear-shaped.)