Footer in Bootstrap 4 alpha

How to set fixed footer in bootstrap 4 alpha :
1). footer {

    position: fixed;
    height: 100px;
    bottom: 0;
    width: 100%;
}

2). use class : <footer class="fixed-bottom">

Sumber :https://stackoverflow.com/questions/19330611/fixed-footer-in-bootstrap and  

 http://v4-alpha.getbootstrap.com/components/navbar/#placement