bug#67638: Description of the variable message-mail-user-agent in Emacs 29.1

[rameiko87]

Dear Eli,

Can you please kindly explain in one sentence where 
message-mail-user-agent and mail-user-agent intervene during the process 
of replying to an email message which I'm reading using Rmail?

> > And also setting the value of message-mail-user-agent to nil: is it 
> > the same as setting the value of message-mail-user-agent to t and the 
> > value of mail-user-agent to Message_withGnusfeatures?
>
> I think so, yes.  But I don't use message.el, so I wouldn't know for 
> sure.  Why won't you try this and report back?

I'm happy to try this, but before I do I must understand what these two 
variables are for.

> > >  The value can be anything accepted by `mail-user-agent', and in addition it 
> > can be nil or t.

I still think this sentence doesn't check out, because the value of 
message-mail-user-agent cannot be "Message package" and 
"Message_withGnusfeatures", which instead are accepted values for the 
variable mail-user-agent.