SDSS J092919.45+033303.4, with specfit analysis results. Top panel: full spectrum as a function of rest-frame wavelength, after normalization at 1350 Å. The actual continuum ranges employed in the fitting of the three spectral regions discussed in the paper are marked. Bottom panels: decomposition of the blends. Black lines: observed spectrum under continuum subtraction. Magenta dashed lines: full model of the observed spectrum. Thick black lines: BC of SiIV, CIV, HeIIλ1640, AlIII and SiIII]. Blue lines: blue-shifted components of SiIV + OIV], CIV and HeIIλ1640. Green line: FeIII(UV34) template. Red line: CIII] emission. Gray lines: faint lines affecting the blends or AlIII BLUE component.