WebReference.com has a new tutorial posted today (from Kris Hadlock) concerning the class inheritance functionlaity that's a part of the object oriented structure in PHP:

There are many benefits of inheritance with PHP, the most common is simplifying and reducing instances of redundant code. Class inheritance may sound complicated, but think of it this way. Consider a tree. A tree is made up of many parts, such as the roots that reside in the ground, the trunk, bark, branches, leaves, etc. Essentially inheritance is a connection between a child and its parent. [...] This article assumes a basic understanding of OOP with PHP.

They show how to create the parent object as a base and how to inherit it into a child class - using the extend keyword in the class definition. They give an example of their sample code in action so you can see how the inheritance is handled.