They represent the minimum and maximum luminance levels of the primary
color volume and the reference luminance level (reference white, SDR
white, ...) in the reference viewing environment.
They help anchoring the white level, optionally help with preserving the
dynamic range and help with adjusting from a "dark" to a "bright"
viewing environment.
The values have defaults which depend on the transfer characteristics.
This reflects the wayland color management protocol.
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/3953>
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