Analogously, the notion of level of grammaticalness does not affect the structure of the ultimate standard that determines the accuracy of any proposed grammar. For any transformation which is sufficiently diversified in application to be of any interest, the speaker-hearer's linguistic intuition is not subject to a descriptive fact. On our assumptions, this selectionally introduced contextual feature cannot be arbitrary in nondistinctness in the sense of distinctive feature theory. Let us continue to suppose that any associated supporting element raises serious doubts about the traditional practice of grammarians. To characterize a linguistic level L, the appearance of parasitic gaps in domains relatively inaccessible to ordinary extraction is to be regarded as the requirement that branching is not tolerated within the dominance scope of a complex symbol.
see also: WikiPedia -- Chomskybot