This extract has been provided by John Lawler (source). The technical term for what we're seeing here is Pied-Piping.
This process, of moving the whole prepositional phrase instead of only its object, is what Pied-Piping means. The preposition gets piped
away to the front, marking its object.
Moreover, prepositional phrases can modify nouns that are objects of
other prepositional phrases, and they, too, are constituents, and can
be moved as a unit. So are, and so can, the noun phrases. Again, only
optionally. Which leads to such mind-numbing spectra of nonrestrictive
relatives as:
The government prescribes the height of the lettering on the covers of the reports.
the reports, **which** the government prescribes the height of the lettering on the covers of
the reports, of **which** the government prescribes the height of the lettering on the covers
the reports, the covers of **which** the government prescribes the height of the lettering on
the reports, on the covers of **which** the government prescribes the height of the lettering
the reports, the lettering on the covers of **which** the government prescribes the height of
the reports, of the lettering on the covers of **which** the government prescribes the height
the reports, the height of the lettering on the covers of **which** the government prescribes