Found:

Functional Projection

SYNTAX: The syntactic Xbar projection of a functional head, such as COMP (CP), INFL (IP), or Det (DP). The underlying assumption is that, like lexical heads N, A, V and P, functional heads have a syntactic projection as dictated by X-bar theory. A fundamental question is whether there is a limit to the number of functional categories. It seems reasonable to assume that their projection is in some sense parasitic on, or an extension of, a lexical projection.

LIT.	Abney, S. (1987) Chomsky, N. (1986b) Ouhalla, J. (1990)