Two attributes are 'identifiers'. It is and is a method for an object to 'pass responsibility on'. There are two ways an object can pass responsibility on. One way is that it can forward a message to any other object it has knowledge of. Another way an object can pass responsibility on is to refer all messages that are not understood by the receiving object to the parent object.
Object oriented programming allows for extension of an objects function or of class function.
The ability to change code after it has been developed without necessarily changing the appearance of an object is peculiar to oops. In object oriented programming units of code are called functions. This site is designed use frames.