Transfer characteristics imply absolute luminance in reference viewing environment
Choosing a transfer characteristic for an image description must also imply the luminance range and reference white luminance. A lot of specs don't do a good job at specifying both the luminances and the viewing environment so falling back to a generic "SDR" range for them should be possible when they are close enough. The protocol should explain all of this.
To support content that matches the actual display and the actual viewing environment a way to override this implied range must be supported (!44).