Specifies a static value that is used by the WPF property system rather than a null reference (Nothing in Visual Basic) to indicate that the property exists, but does not have its value set by the property system.
Assembly: WindowsBase (in WindowsBase.dll)
is a sentinel value that is used for scenarios where the WPF property system is unable to determine a requested DependencyProperty value. is used rather than a null reference (Nothing in Visual Basic), because a null reference (Nothing in Visual Basic) 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.
Setting a DefaultValue of is specifically disallowed.
DependencyObject.ReadLocalValue returns when the requested property has not been locally set.