bootstrap/docs/_includes/nav/migration.html

The most popular front-end framework for developing responsive, mobile first projects on the web.

<li>
  <a href="#classes">Major class changes</a>
</li>
<li>
  <a href="#new">What's new</a>
</li>
<li>
  <a href="#dropped">What's removed</a>
</li>
<li>
  <a href="#notes">Additional notes</a>
</li>