With the next link in their look at the "chain of responsibility" pattern, DevShed has posted this new part in the series - adding an error logger to the mix.

At the end of this article you should be equipped with more robust knowledge of how to create a responsibility chain between PHP objects that perform truly useful tasks, like logging errors to specific components of a Web application.

They work from the code built up in the previous installations and show how to add the foundations of the error logger to the class before moving on to the more advanced bits. They then show how to use it to log some basic errors and, using only a bit more skill, logging some email-related errors.