Why can I FreeAndNil() a Delphi string? That's just wrong on so many levels. But I'm assured that it not only compiles, it runs. Please explain!

Why can I FreeAndNil() a Delphi string? That's just wrong on so many levels. But I'm assured that it not only compiles, it runs. Please explain!

Well, in the "no immediate error" sense. Strangely, just after that I start seeing access violations. Does anyone know why?