By and large, the rules I learned in various English and grammar classes, beyond the initial sentence structure, were prohibitive rather than permissive; there'

By and large, the rules I learned in various English and grammar classes, beyond the initial sentence structure, were prohibitive rather than permissive; there's no rule explicitly _allowing_ arbitrary nesting, because why would need a rule to specify that, but there's also no rule that I'm aware of that _prohibits_ arbitrary nesting. In fact, the "rule" that matters here is general sentence structure. It's fine to embed a single secondary clause inside a primary clause: That's the woman [the house Jack built] fell on. The structure of the inner clause has no further restrictions on it than the structure of the outer clause. Thus, the entire above sentence is perfectly valid as an inner clause to a new outer clause: That's the lawyer [the woman <the house Jack built> fell on] hired. There's nothing in any grammar book that I'm aware of explicitly prohibiting infinite nesting of this sort; it's just silly and quickly becomes unintelligible. Though I definitely take Tenhundfeld's point that this sort of structure is a lot more common in spoken language, and in fact it's a lot more easily comprehensible with the aid of vocal cues and tones.