(g − r, r − z) colour-colour plot. The black lines indicate the selection criteria defined by Akiyama et al. (2018), including the complementary criteria from this work. The small grey points indicate the point-like sources in the 4XXL-HSC sample, while the orange squares represent the high-z candidates in Cases A, B, and C (see text for details). We over-plot the specz-z sample (asterisks) colour-coded with the redshift, while we highlight the dropouts with z_phot ≥ 3.5 in blue.