Role of Mutiple "layout" arguments to go-fiber html Render

Question

I want to understand how go-fiber Render works with multiple layout arguments. It is quite clear how a single layout argument works (the first argument is executed and inserted into the {{embed}} tag inside the first layout argument). I looked at the sources and it appears to my inexperienced golang eye that only layout[0] is used. Can someone familiar with go-fiber templating explain please. Thanks