Top panel: rest-frame composite spectrum (see Sect. 5.1). Abscissa corresponds to vacuum rest-frame wavelength in Å, while ordinate is in arbitrary intensity. Dot-dashed vertical lines identify the position at rest-frame of the strongest emission lines. Bottom panels: multicomponent fits after continuum subtraction for the 1400 Å blend, C IV1549 and 1900 Å blend spectral regions (Sect. 4.2). In all the panels continuous black line marks the broad component at rest-frame associated to Si IV1397, C IV1549, Al IIIλ1860 and Si III]1892 respectively, while the blue one corresponds to the blueshifted component associated to each emission. Dashed pink line marks the fit to the whole spectrum. Dot-dashed vertical lines correspond to the rest-frame wavelength of each emission line. In the Si IV1397 spectral range, the cyan line marks the contribution of O  I1304+Si  II1306 blend, while the magenta line corresponds to the C  II1335 emission line. In the C IV1549 region, the yellow one corresponds to the O  III1663+Al  II1670 blend. In the 1900 Å blend range, Fe III and Fe II contributions are traced by dark and pale green lines respectively, magenta line marks the N III1750 and the yellow one corresponds to the Si II1816. Lower panels correspond to the residuals, abscissa is in radial velocity units km s⁻¹.