What/where are (tab-)animation Classes?

The ion-tab documentation mentions animations, but the link is broken:

Assign any tabs class or animation class to the element to define its look and feel.

http://ionicframework.com/docs/components#animation http://ionicframework.com/docs/components/#tabs

I would love to be able to have an animation between tabs but I can’t find anything (except that it seems to have been possible earlier on)