Observed X-shooter spectrum (ID 5 in Table 1) and synthetic spectra of selected regions that show nitrogen emission lines. The observed spectrum is shown as a solid blue line, while the dotted red line is our best-fitting model. The observed spectrum is corrected for the velocity of the SMC and the barycentric motion. The line identification marks correspond to the wavelengths in the rest frame. Panel a shows the area around the N IV λ4057. Panel b shows the region of N III λλ4511−4523, N V λλ4604, 4620, and N III λλ4634, 4641. The N III and N V lines are not observable in the spectrum. Panel c shows the region of the N IV λλ7103−7129 complex.