When discussing armageddon chess, I've seen the term "bidding" being used a lot. I understand the following:
"In bidding armageddons, players usually communicate privately how much time they're willing to give up to play with their desired color. The player who gives up the most time wins."
I know the basic rules of armageddon chess, but I don't fully understand the process for bidding. How exactly do players "bid"? And, what is the point of doing it privately? Also, are there cases where bidding is not used?