The command will allow player to switch between fighting with both ends of a double weapon as if fighting with two weapons or use a double weapon two-handed, attacking with only one end of it.

double_weapon check
Will show your current stance while wielding a double weapon.

double_weapon on
Will switch to fight with both ends of a double weapon as if fighting with two weapons.

double_weapon off
Will switch to two-handed, attacking with only one end.