If IsThreeState is set to true then the check editor will toggle between three states: checked, unchecked and indeterminate. When the editor is in indeterminate state, the Value and IsChecked properties will return null value.
Target Platforms: Windows 10, Windows 8.1, Windows 8, Windows 7, Windows Server 2012, 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