Top panel: normalised spectrum of J0017+1307 over the absorber H₂ Lyman-Werner band region (black) together with the synthetic profile corresponding to the maximum N(H₂) that is still consistent with the data. Bottom panel: positive residuals expressed in units of standard deviation as derived from the error spectrum, with the corresponding distribution shown in the right panel (red histogram). The green line corresponds to the expected Gaussian distribution of the residuals.