On PHPMaster.com today there's an introduction to Reflection, a feature of PHP that allows you to peer into the code itself and find out metadata like class properties, scope levels and parent classes.

PHP introspection is a common feature in any programming language which allows object classes to be manipulated by the programmer. You'll find introspection particularly useful when you don't know which class or method you need to execute at design time. [...] During this article, you'll see a couple examples of how to use some of the most useful PHP's introspection function and a section dedicated to an API that offers functionality similar to introspection, the Reflection API.

They introduce you to a few different methods including class_exists, get_class and get_class_vars and method_exists. They also briefly mention the "ReflectionClass" that's a part of the PHP Reflection API and how it can be used to make an instance pointing to a current class.