Median composite spectrum of VANDELS sources (grey). The upper and lower panels show zoomed-in regions around the HeIIλ1640+OIII]λ1666 and CIII]λ1909 lines, respectively. The central bandpasses, as indicated in Table 3, are marked in black, while the two local continuum windows are marked in blue and red. The green points and dashed lines indicate the mean flux in the continuum bandpasses and the linear pseudo-continuum.