How the capturing of flags itself works?

How the capturing of flags itself works?
I had a short arguing with LeGaulois about how capturing of flags work. He was surprised how i captured a flag for seconds. I had no time to explane to him, he was upset and left server.Does anybody know, that when a player (for example allied) stays next to a white flag, the white line on display slowly fills with blue, and if in the last second an axis player enters the capturing area, the flag turns into axis flag? There are a few more different situations where you can capture an enemy flag in seconds. Apparently, he did not know about these peculiarities of the game. I believe, that most of players know what i am talking about. If it is so, please, post your comments here and let the rest of players know about this. Thank you!