A class is a collection of variables and functions working with these variables. This defines a class named Cart that consists of an associative array of articles in the cart and two functions to add and remove items from this cart. In PHP 4, only constant initializers for var variables are allowed. None of these will work in PHP 4. This is how it should be done.
Classes can be extensions of other classes.
The extended or derived class has all variables and functions of the base class and what you add in the extended definition. This is done using the extends keyword. You create a named cart the usual way and can now set and get the carts owner. Constructors are functions in a class that are automatically called when you create a new instance of a class. Shop the same old boring stuff.