Earlier quoted context omitted.
I disagree, and FWIW, I find your tone hostile. A prescriptivist would say it follows allowed grammar rules but is still unintelligible. A descriptivist would say it follows common usage patterns but takes it to such an extreme as to be unintelligible. You see this pattern more often with proper names: - That's the house Jack built. - That's the woman the house Jack built fell on. - That's the lawyer the woman the ho…
> At what point does it become "incorrect"? When it becomes unintelligible to most native speakers? Beyond 1 level of nesting. There's no rule allowing arbitrary nesting, nor do people commonly nest beyond 1 level. I'm not sure where you saw hostility in my comment.
Also, which example is 1 level of nesting? I think "That's the woman the house Jack built fell on." is 2 levels nesting, and I frequently hear constructs like that – in speaking. I agree it's rarer in writing though.
For example: What server is that? That's the server the consultant Jack brought in set up.
I'd never write that, because it's confusing. But I will naturally say things like that, without any problem in clarity, because you have more granular control over grouping and pausing, etc. If I said a sentence like that, you might hear it more as "That's the server the-consultant-Jack-brought-in set up."
Anyway, sorry if I misread your tone. It just came across very much as "I know what's right, and you're wrong." That might have been me projecting though. :)