class ParentClass {
    protected function method1(): string {
        return $this->protectedMethod1();
    }

    protected function protectedMethod1(): string {
        return 'parent';
    }
}

class ChildClass extends ParentClass {
    protected function method1(): string {
        return parent::method1();
    }

    protected function protectedMethod1(): string {
        return 'child';
    }
}