I've been using PHP for quite some time now, and I had never heard of class_alias before reading this post by Fabian Schmengler.

Sometimes you want to rename a class or move it to a different namespace. But as soon as it is used anywhere outside the package, this is breaking backwards compatibility and should not be done lightheartedly. Luckily there is a way in PHP to have both, the old class and the new class, while deprecating the old one: class_alias().