Visibility of strong AGN emission lines as a function of the redshift in the wavelength range of the HETDEX survey. The O VI λ1034 emission is usually highly noisy due to strong foreground absorbers, and N V λ1241 is often blended with Lyα. These two lines are thus plotted as dashed lines. The gray shaded region at 0.96 < z < 1.26 shows one representative redshift range where only one emission is visible. We note here that Mg_II λ2799 is the reddest emission we searched in this paper. We leave the search for emission lines of AGN at lower redshifts, such as the [Ne_V] λ3426 emission and the Balmer emissions, for the next data release.