Can you explain what late static binding in PHP is and how it differs from other types of binding?

Late Static Binding (LSB) in PHP is a mechanism that allows static methods and properties of a class to refer to the calling class, rather than the class where the method was defined.

The difference from regular static binding is that with a normal call via self::, the class in which the method is declared is always used, whereas with late static binding via static::, the class that actually called the method (runtime class) is used.

Example:

class A {
    public static function who() {
        echo __CLASS__;
    }
    public static function test() {
        self::who();    // always A
        static::who();  // late static binding
    }
}

class B extends A {
    public static function who() {
        echo __CLASS__;
    }
}

B::test();
// Outputs:
// A (from self::who())
// B (from static::who())

Thus, LSB allows creating more flexible and extendable classes, where behavior depends on the subclass, not just the parent class.