In the Promote section of the End Phase, it says that you promote a unit when all of a player's Commander units have been defeated.
The "Field Commander" keyword explicitly states that the unit is not a Commander.
1) While a Field Commander is active, a player has no Commander on the table. Can they promote a trooper unit, or does the promotion only trigger after a Commander that had been on the table is defeated?
2) Can a player promote a trooper unit during the End Phase after a Field Commander unit has been defeated?
3) If a player starts the game with Commander rank unit that is later defeated, can a unit with the Field Commander keyword be chosen as the new Commander? If yes, would they become a Commander rank as under the Promote rules, or retain their original rank as described in the Field Commander rules?