R23–Ne3O2 diagram, probing the ionisation and excitation of the ISM. R23–Ne3O2 closely resembles the R23–O32 diagram with the additional advantage that the [Ne III] λ3869/[O II] λλ3726,329 ratio is less sensitive to the applied dust-correction, or any wavelength-dependent flux calibrations. JADES galaxies are plotted as in Fig. 5. Fewer literature samples present [Ne III] ratios so we show only SDSS, blueberries, MOSDEF, and the z ∼ 7.7 composite CEERS spectrum from Tang et al. (2023). These are each plotted in the same way as in previous figures.