What happens if a static method that does not exist in the class or its parent is called in a derived class?

If a static method is called in a subclass that does not exist in the class itself or in its ancestors, PHP will throw a fatal error. This is because static methods cannot be dynamically resolved, and calling a non-existent method results in script termination.

Example:

class ParentClass {
    public static function existingMethod() {
        echo "Method exists";
    }
}

class ChildClass extends ParentClass {
}

ChildClass::nonExistentMethod(); // Fatal error: Uncaught Error: Call to undefined method ChildClass::nonExistentMethod()

Therefore, it is important to ensure that the static method being called is defined either in the class itself or in its inheritance hierarchy.