Nevertheless, relational information is to be regarded as the traditional practice of grammarians. Analogously, the appearance of parasitic gaps in domains relatively inaccessible to ordinary extraction suffices to account for an abstract underlying order. It may be, then, that a descriptively adequate grammar cannot be arbitrary in a descriptive fact. It must be emphasized, once again, that most of the methodological work in modern linguistics delimits a corpus of utterance tokens upon which conformity has been defined by the paired utterance test. To provide a constituent structure for T(Z,K), any associated supporting element is unspecified with respect to a parasitic gap construction.
see also: WikiPedia -- Chomskybot