For custom animation, I mean something like Clear does.

Many existing questions like [this](https://stackoverflow.com/questions/7504546/view-based-nstableview-with-rows-that-have-dynamic-heights) talks about dynamic height, and I wonder how to create a new row with dynamic height, using animation.

e.g. The animation of showing this:

[![enter image description here](https://i.stack.imgur.com/OsTqH.png)](https://i.stack.imgur.com/OsTqH.png)