SDSS spectrum of SDSS J1251+0613 (blue dots plus error bars) and the composite spectrum of SDSS quasars (dashed red line) from Vanden Berk et al. (2001). The composite spectrum is scaled with the continuum intensity about 52 × 10⁻¹⁷ erg/s/cm²/Å at 5000 Å. The vertical dashed lines in dark green mark the positions of the commonly apparent and strong forbidden and permitted narrow emission lines in blue quasars.