The UV diagnostic diagrams plotted O III] λ λ 1661,1666/He II λ1640 vs. C IV λ λ 1548,1551/C III] λ λ 1907,1909 (left) and O III] λ λ 1661,1666/He II λ1640 vs. C IV λ λ 1548,1551/He II λ1640 (right panels) for the fully radiation-bounded NPI models with mass-loading rates ﹩\mathrm{log}{\dot{M}}_{\mathrm{sc}}=-4﹩, −3, −2, and −1 M _⊙ yr⁻¹ (from top to bottom), ambient densities n _amb = 1, 10, 10², and 10³ cm⁻³ (labeled on plots), metallicities ﹩\hat{Z}\equiv Z/﹩ Z _⊙ = 1 (blue), 0.5 (red), 0.25 (green), and 0.125 (yellow color), and wind velocities V _∞ = 250 (dashed), 500 (dashed–dotted), and 1000 km s⁻¹ (dotted lines). For the subsolar models, we use the solar model parameters scaled as ﹩{\dot{M}}_{\mathrm{sc}}\propto {Z}^{0.72}﹩ and V _∞ ∝ Z ^0.13. The optically thin and thick models are plotted by filled and empty circles, respectively. The wind catastrophic cooling (CC) and catastrophic cooling with the bubble (CB) modes are labeled by the plus (“+”) and cross (“×”) symbols, respectively. The CPI results from Paper II are shown by lightly shaded colors. The plotted observations are from Berg et al. (2016), Amorín et al. (2017), and Senchyna et al. (2017).