That event is raised only when submit of ContentUrl was triggered by tab change or by mouse click on already selected tab.
Action can be canceled. Second param in handler is instance of TabItemCancelEventArgs class, which provides information about TabItem.
Requirements
Target Platforms: Windows 10, Windows 8.1, Windows 8, Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2
