Found:

complement

**SYNTAX: **YP in [_{H'} H YP], where H is a head and H' the projection of H. According to **X-bar theory**, the complement
of a head X^{0} is defined either as a position attached or adjoined to X', or as a **sister** of X^{0}. Thus, in configuration (i), either A and B are complements of X^{0}, or just B (the sister of X^{0}).

(i) X' /| / | A X' /| / | B XSometimes, the complement of a head X^{0}

LIT. | Chomsky, N. (1986a) Chomsky, N. (1981) Williams, E. (1980) |