The root class of most CoreAnimation class hierarchies, from which subclasses inherit a basic interface to the runtime system and the ability to behave as NSObject objects..
a NSObject can use isKindOfClass<T> to check out the class hierarchies.
__strong, __weak and __autoreleasing can apply to NSObject classes.
all the NSObject should use NSObject::allocT<T>() classified method to create object, and call NSObject::release() member method to release it.
any local value or operator new are forbidden. also you can not operator delete it.