Is a Choice

Set this to declare that this Model is a Choice, and its Instances are the options to choose from. -- Collection: Required Type: TrueOrFalse Type

If you set this to True on a Model, it means that this Model is special -- its Instances are an exclusive list of options to choose from. In this case, the Editor will know not to offer to create new Instances when you are choosing one.

In the near future, this will become automatic with the new Multiple Choice Type, and you won't need to use it manually.