Moderator warnings
 

I have been on this forum long enough to see warnings/bans placed on a couple of members, but I have been wondering: How does the warning system work? I checked the forum rules and there is nothing in that spot describing the system.

Offenses cause edits. Grave offenses or a large quantity of offenses cause subwarnings (0.5 warning) or warnings. 3 warning points cause a short ban, if it's your first time. Bans get longer every time you're banned, generally.

Once unbanned you're on a stricter leash and the warning count before you're banned might either be halved or offenses punished more gravely, depending on how admins deal with the lack of a consistent system. It just means: watch out.

Bans need to be confirmed by at least one other admin, and ban length needs to be confirmed by two. So if you're banned it's usually by some form of concensus amongst the active admins, never an individual opinion.

Do the warning points accumulate over time, or do they expire?

They accumulate over time.

Double accounts, registering just to spam or troll, things like that.

A ban for the second account and a warning for the first? Or a ban for both?

A ban for the double account, the consequences for the primary account aren't set in stone.