Brandon Savage has posted the next part of his series looking at exceptions in PHP. This new article shows how to create a custom exception layer on top of the built-in handling.
One of the things that you can (and should) do with PHP exceptions is extend them to suit your own purposes. While the base Exception class in PHP is neither abstract nor impossible to use on its own, extending exceptions give you a great amount of flexibility and power, particularly in three areas: customization, identification, and abstraction.
He looks at creating custom exception types (for easier handling and customization and how it can help with the abstraction of your applications.