How to combine PlutoUI widgets into new widgets?

I came across this tutorial, but it seems that the code is no longer working in the latest stable version of Pluto/PlutoUI:

The tutorial explains how to use PlutoUI.combine() to create new widgets from existing ones. Is there an updated version of the tutorial somewhere with working code?

In particular, how to write a function that creates a list of sliders and binds them to a vector variable?

Here is the relevant discussion in the development channel of Pluto on Zulip: