[O III]5007 Å/[O III]88 μm versus [O III]5007Å/Hβ diagram. Top and bottom panels show model grids computed with Cloudy with metallicities Z/Z_⊙ = 0.05 to Z/Z_⊙ = 0.2, respectively. Each model grid spans a range of ionization parameters (−3.5≤log U≤−1) and hydrogen densities (10 cm⁻³≤n_H≤10⁴ cm⁻³) in steps of 0.5 dex. Details on model parameters are provided in Table 1. The magenta-shaded regions show the plausible attenuation-corrected line ratios for JADES-GS-z14-0 inferred from observations by JWST/MIRI and ALMA. The dark regions report the range of line ratios assuming that the MIRI excess is only due to the optical line. The light regions illustrate the range of line ratios in the case the stellar age is 1 Myr and there is an inverse Balmer break in the spectrum. The gray arrow represents a reddening vector with A_V = 0.25 assuming the nebular dust attenuation follows an average SMC extinction curve.