L_X − L_UV relation in the redshift bins reported in the sub-titles. The sensitivity surfaces at the minimum, median and maximum redshift of the bin are represented in red with a full area, a dashed line and a shaded area respectively. These surfaces are obtained from the sensitivity lines in Fig. B.1 at the above-mentioned redshifts. The sources above the shaded sensitivity area in each z-bin give the cleanest XMM-XXL sample.