Analysis of the 1900 Å blend and the [O II]λ3728 region (small box within the figure) as described in Sect. 3.2. The abscissa scale is rest frame wavelength in Å. The ordinate scale is the specific flux in units of 10⁻¹⁷ ergs s⁻¹ cm⁻² Å⁻¹. Top: example of a Pop. A source fitted with a Lorentzian profile. Bottom: example of a Pop. B source fitted with a Gaussian profile. The black lines identify the BC of Al IIIλ1860, Si III]λ1892, and C III]λ1909 (red and grey lines are the VBC and NC of C III]λ1909, respectively, if present). The dashed blue line is the multi-component model obtained by specfit. Green lines trace the adopted Fe II (pale) and Fe III templates (dark).