The extent is either the width or the height of the target, depending on the SplitterDragEventArgsBase.SplitterOrientation. When the splitter orientation is vertical, the newExtent represents the new width. When the splitter splitterOrientation is horizontal, the newExtent represents the new height.
The newTargetExtent will be constrained by the SplitterDragInProgressEventArgsBase.MinTargetExtent and SplitterDragInProgressEventArgsBase.MaxTargetExtent.
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