Observed spectrum of SDSS J014828+150221 (solid black) in the region of the Mg ib triplet with the best fit superimposed (solid pink). The green boxes enclose the range for the fit on the Mg i lines, the light-blue box that for the fit on the Fe ii line. The magenta horizontal solid lines represent the continuum, the magenta horizontal dashed lines represent one σ of the S/N of the observed spectrum in the region, and the magenta horizontal dotted lines represent three σ of the S/N. The magenta vertical solid lines show the wavelength at the centre of the fitting range at rest, and the magenta vertical dashed lines show the same after the shift assumed by the fitting.