A key with a corresponding value in the thread dictionary.
If you need to customize the behavior of NSAssertionHandler, create a subclass, overriding handleFailureInMethod:object:file:lineNumber:description: and handleFailureInFunction:file:lineNumber:description:, and install your instance into the current thread’s attributes dictionary with this key.
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)