This panel lets you specify which units are available to each player. On the left side of the panel is a tree control with all the units in the game and a list-box with all of the players.
To the right of the tree control is an Enable by Default checkbox. A unit marked as enabled will be available in games played on this map.
Initially, all units are available. To disable a unit for all players, select the unit in the tree control and then uncheck the Enable by Default checkbox.
Initially, all players are set to use the default settings for the availability of units, but you can modify unit availability for each player separately. To change the availability of a unit for one player, select the player in the list-box and select the unit in the tree-control. Then, uncheck the Use Defaults for Player checkbox. You can then check or uncheck the Enable for Player checkbox as appropriate.
The list-box updates automatically to show if a player is using the defaults for the selected unit and, if not, to show whether that unit has been enable or disabled for that player.