How to store per-server backend state

[Nikolaus Rath]

Hello,

I'd like to store some server-specific data for the imap backend. What's
the best way to do that?

The gnus manual recommends to do that by keeping an alist of virtual
server environments and claims that the standard backends use this
technique. However, I could not find no such alist for the nnimap
backend. Am I just missing it, or is there really no per-server state
maintained?

In the latter case, what backend should I look at for a good example on
how do use this technique?

Thanks,
-Nikolaus