While PHP compatibility is a classic quest, compatibility frameworks is an uncharted new territory. With each version of the foundation code, new classes, methods and arguments appears, while other fade away: this is the fast pace of modern evolution. And it is a lot easier to keep up with an automated tool.

We introduce the PDFF archive. PHP Document File Format is an open source format. It provides an encyclopedic description of the OOP API. Static analysis tool take full advantage of this knowledge to audit the code and identify discrepancies.

Best of all, PDFF is both machine and human friendly : it serves as documentation, by listing all structural evolutions, and help cross the versions gap : that includes the upcoming ones.