Recently, I was told by someone in my playgroup that you cannot take control of a player's commander at any point. If an effect would cause you to control another player's commander, either the effect fizzles or the commander goes to the command zone, I forget which he said.

The thing is, I searched mtgcommander.net, and another website that pointed to mtgcommander.net as the source of the official rules of EDH, and I can't find that particular rule anywhere.

Can someone please clarify? At any time are you allowed to control another player's commander? If so, then the next logical question is if I deal 21 combat damage to a single player with someone else's commander, does that player then lose the game?

It would seem that this question is answered indirectly here and here, but I wanted a more definitive answer to the question.

Recently, I was told by someone in my playgroup that you cannot take control of a player's commander at any point. If an effect would cause you to control another player's commander, either the effect fizzles or the commander goes to the command zone, I forget which he said.

The thing is, I searched mtgcommander.net, and another website that pointed to mtgcommander.net as the source of the official rules of EDH, and I can't find that particular rule anywhere.

Can someone please clarify? At any time are you allowed to control another player's commander?

It would seem that this question is answered indirectly here and here, but I wanted a more definitive answer to the question.