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.

<?php

// Superclass
class Bird
{
    public function canFly()
    {
        return "Unknown";
    }
}

// Subclass
class Sparrow extends Bird
{
    public function canFly()
    {
        return "Yes, I can fly!";
    }
}

// Subclass
class Penguin extends Bird
{
    public function canFly()
    {
        return "No, I prefer swimming.";
    }
}

$sparrow = new Sparrow();
$penguin = new Penguin();
echo "Sparrow says: " . $sparrow->canFly() . PHP_EOL;  // Output: "Yes, I can fly!"
echo "Penguin says: " . $penguin->canFly() . PHP_EOL;  // Output: "No, I prefer swimming."

?>