The Orientation property determines how the MdiTabGroup objects in the TabGroups collection are laid out. When there is only 1 tab group and the MaxTabGroups is greater than 1, the end user may create either a Horizontal or Vertical tab group by either dragging a tab near the edges of the mdi client or using the context menu. Setting the AllowHorizontalTabGroups to false (true is the default value), will prevent the user from being able to create a horizontal tab group. Also, if this property is set to false, the user will not be able to create additional horizontal tab groups.
Note: This property only affects the ability to create horizontal root tab groups. When true and AllowNestedTabGroups is true and the Orientation is vertical, dragging and releasing a tab within a few pixels of the outside top or bottom mdi client edge will create a new tab group for the tab and another that will be used to nest the tabgroups that existed in the TabGroups collection. The orientation will then be toggled to horizontal.
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