Behaviour of Al IIIλ1860 (left) and C III]λ1909 (right) by population. a),b): shift with respect to rest frame vs. FWHM. c),d): shift vs. log L_bol. e),f): ratio of shift over FWHM vs. R_Edd. g),h): FWHM vs. log L_bol. Lines are the luminosity-dependent limit between Pop. A and Pop. B. of Sulentic et al. (2017, gold) and the empirical separation of Sulentic et al. (2000c, dashed). Colour-coding: Pop. (blue circles), Pop. xA (magenta stars), and Pop. B (red squares). Reported values are sub-sample medians, error bars are sIQRs. Marker sizes are as indicated in the legend of each plot.