Top panel: fit of the Mg II region in the 2016 May 30 TNG spectrum. The black solid line is the observed flux, the blue solid line indicates the continuum power law (slope α_λ = −1.02 ± 0.08), the green solid line represents the Fe II multiplets, the orange solid line is the narrow component of Mg II, the purple solid line indicates the Mg II broad component, while the red dashed line represents the best-fit model, obtained by adding all of the previous components. Bottom panel: residuals between the data and the model, in units of 10⁻¹⁷ erg s⁻¹ Å⁻¹.