Putting rules in other rules

[Tabbourg]

In the Nothing video he drags the tadpole into another rule "Just like any other square". How do I do this? Just dragging doesn't seem to work.

[TodePond]

when you click on a paddle, the multi-square appears in your toolbar at the top of the screen. or right click and drag the paddle

warning very buggy if you try to make a square that isn't a square