ControlProperty is a reactive wrapper for a property of a UIElement, such as UITextField's Rx.text ControlProperty is a reactive wrapper around its text property. ControlProperties are defined in the Rx namespace. This helps separate and distinguish them from the standard library properties and methods. Generally, but not always, they use the same name as the standard library implementations that they wrap. Like Driver, a ControlProperty will also replay its latest element to new subscribes if there is one, and ControlProperty will automatically emit a completed event when its control or view is about to be deallocated.