Represents the number of user actions necessary to reach the view controller. An increased visibility depth indicates a higher number of user interactions for the view controller to be visible again. For example, an onscreen navigation controller’s top view controller should have a visibility depth of 0. The view controller one from the top should have a visibility deptch of 1 as should the root view controller in the stack (because the user can hold the back button to pop to the root view controller).

Visibility depth is used to automatically adjust ranges on range controllers (and thus free up memory) and can be used to reduce memory usage of other items as well.