In what scenarios would using parent:: versus self:: in PHP be more appropriate when calling functions within a class hierarchy?

When calling functions within a class hierarchy in PHP, using `parent::` is more appropriate when you want to specifically call the parent class's implementation of a method, even if it has been overridden in the child class. On the other hand, using `self::` is more appropriate when you want to call the current class's implementation of a method, regardless of any overrides in child classes.

class ParentClass {
    public function someMethod() {
        echo "ParentClass implementation";
    }
}

class ChildClass extends ParentClass {
    public function someMethod() {
        parent::someMethod(); // Calls ParentClass implementation
        echo "ChildClass implementation";
    }
}

$child = new ChildClass();
$child->someMethod();