Model of the rest-frame spectrum of I20210N. Upper panel: full I20210N spectrum (black solid line), along with the best-fit starlight model adopted for continuum subtraction (yellow dot-dashed line), the best-fit reddened emission profiles (green short-dashed lines), the global spectral model (red solid line), and the masks applied to the telluric absorption lines (grey bands) shown superimposed to the data. Lower panels: zoom on the continuum-subtracted emission lines (black solid line), shown along with the global best fit (red solid line) and the best-fit single components (green short-dashed lines) for the blended [O II] doublet, Hα+[N II] and [S II] transitions. The standardized residuals after the best-fit subtraction are also shown in separate windows below each spectral region. In all panels, the zero-level flux (black long-dashed line) is indicated; in the panel with Hα+[N II] and [S II], the masks applied to the telluric absorption lines (grey bands) are shown superimposed to the data.