What I can't work out how to do though is to work in UHD at Rec. 2020. This seems to be a pretty standard delivery requirement with no clear way to impliment in PP.
I can set the colour space of footage coming in to Premiere to be Rec. 2020, but it seems like you either have to put that in a Rec. 709 sequence or a Rec. 2100 one. So how can I be sure that my colour gamut is correct if it is a Rec. 709 sequence, or that my levels are correct if it is a Rec. 2100 sequence?
For instance, in a Rec. 2100 sequence text seems to be generated at 1000 nits (which is incorrect even for HDR - 203 nits is the generally agreed levels for graphics white).
I should add, in the Project Settings menu you can set HDR Graphics White (Nits) to 100 which does fix the generated text levels - they will then be 100 nits. Maybe there is an issue with naming of the colour management? 100 nits and wide Colour gamut is Rec.2020 (technically I think Rec. 2020 only describes the color gamut and not the brightness range, where as Rec. 2100 describes the color gamut and the 1000 nits of max luminance).
As it is I find it very difficult to have confidence in what PP is doing. I would appreciate other peoples opinions and experiences of this.