The latter are rankshifted into the nominal complement slot of clefts, whereas the antecedents of NRRCs display the structural assembly congruent with their rank.
However, the "non-NP" units functioning as complement in clefts are rankshifted into the nominal complement slot and are in this sense "nominalized" (Halliday 1985: 219).
I propose that it is precisely the "rankshifted," nominalized, status of such antecedents in clefts that explains their resistance to relative adverbs such as when, where, etc.
If the complement in clefts is realized by a rankshifted element such as adverb, prepositional phrase, or clause, then its semantic profile is that of a -- reified -- entity.
Prepositional phrases and clauses are rankshifted into the nominal complement slot and are reclassified as definite NPs.
Note also that the enumerating complement in there clefts accepts fewer types of rankshifted units than the identifying complement in it clefts.
But there can be no doubt that it clefts allow for a greater variety of rankshifted units than there clefts.
"Ordinary" enumerative existentials do not, of course, predicate any equation and do not normally contain rankshifted units.
In the latter case, we have rankshifted units that "quote" the form of the original class but superimpose the functions of a definitely identified NP on them.
The rankshifted antecedent of the RC in clefts still displays the class that matches up with the function of the relative pronoun.