Basic Customization > User Interface Customization > Adding Actions and Hooking Them Up in the UI > Tab Models > Objective > Background > Scope/Applicability/Assumptions
  
Scope/Applicability/Assumptions
Assume you need to add a new tab to the main navigation of the navigator.
Assume you need to remove an existing tab from the main navigation of the navigator.
Assume you need to add/remove links in the second level navigation.