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.)