S2-BPT (S. Veilleux & D. E. Osterbrock 1987) showing SDSS z ∼ 0 galaxies (gray contour lines), KBSS LBGs (S17; gray dots with 3σ detections for every line), a stack of high-z galaxies from R. L. Sanders et al. (2023), CECILIA faint LAEs (pink circles with 2σ limits), CECILIA D40 (purple circle), a Lyman-break galaxy from A. J. Cameron et al. (2023), and CECILIA faint LBGs (pink squares). The solid black line is the classification curve used by L. J. Kewley et al. (2001) to divide the theoretical starburst region from objects of other types of excitation.