Represents the relationship between an instance of this model and the controller account.
'list' means there can be many instances of this model for a single account. 'single' means
there can be only one instance of this model per account (if a new instance is created it
overrides the old one).
Represents the relationship between an instance of this model and the controller account. 'list' means there can be many instances of this model for a single account. 'single' means there can be only one instance of this model per account (if a new instance is created it overrides the old one).