Signer's User ID

Hello!

I'd like to have a clarification of the signature subpacket

  5.2.3.22. Signer's User ID

    (String)

    This subpacket allows a keyholder to state which User ID is
    responsible for the signing. Many keyholders use a single key for
    different purposes, such as business communications as well as
    personal communications. This subpacket allows such a keyholder to
    state which of their roles is making a signature.

    This subpacket is not appropriate to use to refer to a User
    Attribute packet.

It is not clear to me whether the string should be a verbatim copy of
the content of a User ID packet or some other information.  The second
paragraph could be viewed as a hint for a verbatim copy.

OTOH, for applications it makes more sense to have just the vanilla
mail address (mailbox(_at_)domain) here.  This would make it easier to
compare a mail's From address to the actual signature.

I don't care much about this but given that such a subpacket has been
defined but is not widely used - if at all - we might want to define
it in a stricter way.


Shalom-Salam,

   Werner