Nice work @subcritical71
I had a quick look at the UK situation
The basic rules are in The Road Vehicles Lighting Regulations 1989 Shedule 12,
10. Electrical connections–
(a) Every stop lamp fitted to–
(i)a solo motor bicycle or a motor bicycle combination first used on or after 1st April 1986 shall be operated by the application of every service brake control provided for the use of the rider;
(ii)any other motor vehicle, shall be operated by the application of the service braking system.
(b) Every stop lamp fitted to a trailer drawn by a motor vehicle shall be operated by the application of the service braking system of that motor vehicle.
There is also an EU directive 91/663/EEC which says:
4.7.7 Electrical connections
Stop lamps must light up when the service brake is applied . They need not function if the device which starts and / or stops the engine is in a position which makes it impossible for the engine to operate .
Since this 1991 directive confirms the 1989 UK Law there was no need to amend the UK law. And since they are both from 30 years ago have no specific mention of regenerative braking.
However, the term “service braking system” might be argued by the lawyers to be anything that slows the vehicle faster than the “natural” deceleration rate when drive power is removed.
At some point I would expect the U.N. description will be adopted here. Rather like the directives on In Car Child Restraints and their use, the UK rules for which started in the U.N. , were confirmed in the EU and were then incorporated into UK Law.
Fortune favours the prepared; she has no favourites and takes no sides.
Truth is confirmed by inspection and delay; falsehood by haste and uncertainty : Tacitus