In this new post to his blog Brandon Savage takes a look at multiple inheritance in PHP applications - specifically where it could "kill you" if you're not careful.

This is a fantastic way to further encapsulate and abstract your code because it means you can define some base functionality and then later on extend that class to add new functionality and even override existing functionality to make the class specific. But this concept is a double-edged sword in PHP (and all other languages).

The problem lies in methods in classes that could be overriding parents and the sort of results that instance of might return in a multiple inheritance environment. He includes code snippets both illustrating the problem and showing a suggestion for how it could be avoided.