Property. Unset Value Field
Specifies a static value that is used by the WPF property system rather than
null to indicate that the property exists, but does not have its value set by the property system.
public: static initonly System::Object ^ UnsetValue;
public static readonly object UnsetValue;
staticval mutable UnsetValue : obj
Public Shared ReadOnly UnsetValue As Object
UnsetValue is a sentinel value that is used for scenarios where the WPF property system is unable to determine a requested DependencyProperty value. UnsetValue is used rather than
null could be a valid property value, as well as a valid (and frequently used) DefaultValue.
A dependency property has a default value established in metadata and that value is returned. This value might come from DefaultMetadata.
Some other value was established by the property system, and the default value is no longer relevant. For details, see Dependency Property Value Precedence.