Determines whether the control supports two or three states.
Assembly: PresentationFramework (in PresentationFramework.dll)
XMLNS for XAML: http://schemas.microsoft.com/winfx/2006/xaml/presentation, http://schemas.microsoft.com/netfx/2007/xaml/presentation
Metadata properties set to true
The IsChecked property can be set to a null reference (Nothing in Visual Basic) as a third state when is true.