Hello, learner! In today's exciting chapter, we will explore how PHP handles backward compatibility when introducing new features. This is akin to a software update that adds new functionalities without breaking the existing ones. With PHP's object-oriented programming capabilities, we will discover effective methods to achieve this balance.

In PHP, class inheritance and method overriding enable objects to take on multiple roles. This allows methods to be defined in a base class and then overridden in derived classes for specific behavior. Let's consider an example with a Bird class and subclasses like Sparrow and Penguin to illustrate this concept.

When adding new features in PHP, class inheritance supports backward compatibility by allowing the existing functionality to remain unchanged while new behaviors are introduced. Unlike method overloading, PHP uses optional parameters and argument checks to manage varying function inputs.

Consider a MathOperations class with a method supporting different numbers of arguments. We can extend this class with new methods in a way that the old functionality remains untouched.