Best way to allow plugins for a PHP application

Question

I am starting a new web application in PHP and this time around I want to create something that people can extend by using a plugin interface.

How does one go about

Answer 1

There's a neat project called Stickleback by Matt Zandstra at Yahoo that handles much of the work for handling plugins in PHP.

It enforces the interface of a plugin class, supports a command line interface and isn't too hard to get up and running - especially if you read the cover story about it in the PHP architect magazine.