Ionisation parameter and metallicity sensitive log(O₃₂) = log([O III] 5007/([O III] 3727) vs. log(R₂₃) = log(([O II] 3727 + [O III] 4959 + [O III] 5007/Hβ diagram. Symbols are the same as in Fig. 2. Additional markers were added for several low-z LyC leakers, i.e. the GPs from Izotov et al. (2016a,b, 2018a,b, green upward triangles) and low-mass galaxies from Izotov et al. (2021b, cyan left-facing triangles). Also shown are the intermediate-z LyC leakers Ion2 from de Barros et al. (2016, orange pentagram), four galaxies from Fletcher et al. (2019, dark red hexagrams, where we converted their listed [OIII] 4959,5007 values to [OIII] 5007 assuming [OIII] 5007/[OIII] 4959 = 2.98, Storey & Zeippen 2000), and AUDFs01 from Saha et al. (2020, purple right-facing triangle). The SDSS DR12 galaxies (black scatter diagram) are limited to those identified as SFGs with the BPT diagnostics from Kewley et al. (2001) and Kauffmann et al. (2003).