Example of UV spectral fitting. Best-fit model (left panel, orange curve) and residuals (right panel, in units of 1σ uncertainties on the data and cumulative reduced χ²) are presented for Ark 120. Redshift and Galactic extinction at the source location are shown on top of the plot. The main model components are plotted with different colours: the solid red line is the sum of continuum and host galaxy components; the black solid line is the absorption component; the dot-dashed green line is the Balmer component; the solid green line is the UV iron template; the sum of all broad and narrow emission-line components is shown with blue and brown lines, respectively. The red square symbols are the continuum luminosities estimated by QSFit.