6.2. The PHP 5 Object Model
PHP 5 has a single-inheritance, access-restricted, and overloadable object model. Inheritance, discussed in detail later in this chapter, involves a parent-child relationship between classes. Other languages allow for multiple parents; PHP allows for one parent per child. Additionally, PHP supports restricting access to properties and methods. You may declare members private, disallowing access from outside the class. Finally, PHP allows a child class to overload the members of its parent class.
The object model in PHP 5 treats objects differently from any other kind of value that is available in PHP and implements implicit, pass-by-reference behavior. That is, PHP does not require you to explicitly pass or return ...
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