When the Orientation of the tab groups is Horizontal, this value indicates the height of the group; otherwise the value indicates the width of the group. The Extent includes the area occupied by the splitter, if there is one for the MdiTabGroup. A splitter is allocated for all MdiTabGroup instances in the TabGroups except the last one. The ClientExtent property can be used to initialize the Extent without determining whether the tab group displays a splitter bar.
Note: Changing the extent of a tab group after a call BeginUpdate and before the call to UltraTabbedMdiManager.EndUpdate, will not affect the extent of the other MdiTabGroup objects in the TabGroups until the EndUpdate is invoked. At that point, the sum of the extents is verified against the extent of the mdi client area. If the sum does not match the extent of the mdi client area, the extents are adjusted.
Target Platforms: Windows 10, Windows 8.1, Windows 8, Windows 7, Windows Server 2012, 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