Note: Separators are skipped. Only tabs are considered. For example, if there is a separator between 1st and 2nd tabs and 2nd tab is selected, then this property will return value 1, but index of that TabItem within Tabs collection is equal to 2.
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