Someone posted 92 mb zip of some 2015-2017 era reading material for this new 'HDR' thing.

May be you can find original link on doom9 but here is copy, hopefully:

https://drive.google.com/file/d/1SCIqdqM4ZNBpN02zxmGe1hchpVUyqgcr/view?usp=drivesdk