```
Now $classInstance has all the methods from MySuperClass1 and MySuperClass2. Since MySuperClass2 is being used as a behavior, it has to extend CBehavior.
The only caveat to this is an attached behavior cannot override any class methods of the component it is being attached to. If a method already exists, if it be from the original class or already added by a previously attached behavior, it will not be overwritten.


In an OO language like Ruby, it's quite possible to start with an completely empty object and simply build its behavior as you go along. Yii provides this behavior with a little magic. The key is that the class you wish to add the behavior from must extend Cbehavior.So, in this case, you are extending the functionality of an object with functionality of another object.

After studying this cookbook page it isyou are encouraged to reread the [corresponding guide page](http://www.yiiframework.com/doc/guide/basics.component) as it contains advanced information (for example, if you are familiar with interfaces, you might find it enough to implement IBehavior before extending CBehavior).