Median stacked 1D rest-frame emission-line spectrum of the full sample of 792 [O III] emitters at z = 5.5–7. Each galaxy spectrum has been normalised by its ([O III]λ5008+2.98[O III]λ4960)/2 flux before stacking. The shaded green region shows the uncertainty estimated through bootstrap resampling. We highlight the wavelengths of Hδ, Hγ, [O III]λ4364, Hβ, [O III]λλ4960, 5008, and HeIλ5877. For visualisation, we normalised the stacked spectrum by the Hβ luminosity such that Hβ peaks at unity.