EV1 plane FWHM(Hβ) vs. r_Fe II. The distribution of a subset of SDSS DR16Q quasars from Wu & Shen (2022) is shown in black (see text for selection criteria). The colourmap gives the mean log₁₀EW([O III]) in bins of size Δ r_Fe II = 0.1 and ΔFWHM(Hβ) = 500 km s⁻¹. J0313-1806 is shown as a green star. WLQs from Chen et al. (2024) are shown as circles (measured EW([O III] λ5007)) or triangles (upper limits), colour-coded according to their log₁₀EW([O III]). J0313–1806 and several WLQs lie outside the xA regime (r_Fe II > 1) but nonetheless show strikingly weak [O III] λ5007 emission compared to SDSS DR16Q quasars in the same EV1 bins.