[css-color-hdr] HLG display issue, system gamma depends on monitor peak white

Author: svgeesus

css-color-hdr/Overview.bs

@@ -397,6 +397,8 @@ must map SDR media white
 to the same luminance as is used
 to display the 75% HLG value.
 
+Issue: see also tables 3 and 4 in ITU Rec.2408-0
+
 Absolute HDR using the PQ transfer function
 should map SDR media white
 to 140 cd/m², the same luminance as is used