GNU-divert-to-card S2K format

[Léonard Dallot]

Hello,

I am trying to write a program that read GPG privates keys that have
been exported to a GPG smartcard using GPG. Those keys are encoded
unsing a S2K Specifier that is described in RFC 4880 as
"experimental" (Tag 101). GPG (using gpg --list-packets) describes this
as "gnu-divert-to-card S2K", followed by a serial number.

I have tried to find a description of this S2K format, but I haven't
found one. Does anyone know where I can find a description of this
"experimental" S2K ?

Thanks a lot for your help,
Léonard