Default value is set to the "dummy.htm".
If the value is set to the empty string, then <IFRAME> elements are not written to html for tabs with an empty TargetUrl. In this situation the client side function setTargetUrl is not available for those tabs.
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