An NSNumber object containing a Boolean value that determines whether the value of the binding is updated as edits are made to the user interface item or is updated only when the user interface item resigns as the responder.
Available in Mac OS X v10.4 and later.
Declaration Syntax Version Information- Available in Monobjc Bridge: 10.6 (For Mac OS X 10.6 and later), 10.5 (For Mac OS X 10.5 and later)